Nematodes - cowpea

Contributors to this section: IITA, Nigeria (M. Ayodele, L. Kumar).

Contents: Root-knot nematodes Reniform nematodes

Root-knot nematodes

Scientific name

Meloidogyne arenaria.

Other scientific names

Meloidogyne incognita (Kofoid & White, 1919) Chitwood 1949
Oxyuris incognita Kofoid & White, 1919
Meloidogyne incognita acrita Chitwood, 1949
Meloidogyne acrita Chitwood, 1949

Importance

High

Significance

The nematode attacks many major food crops resulting in reduction in quality and quantity of food and feed .Yield loss ranges from 5%- to   complete loss (Sasser and Carter, 1984).

Symptoms

The nematode affects the  flowering, podding, seedling and vegetative growing stages. The leaves, roots and whole plant are also attacked by the nematode causing different symptoms on:

roots/ corms/ tubers: galls, abnormal formation and function of root system and blockage of; the vascular cylinder.

stem ( above the ground )symptoms : patchy, stunted growth; discoloration and

leaf : chlorosis, wilting

whole plant : stunting, reduced yield in quantity and quality; premature; death.

Hosts

The nematode has alarge host range which includes monocotyledons, dicotyledons, herbaceous and woody plants.

The major hosts include Vigna unguiculata (cowpea), Abelmoschus esculentus (okra), Arachis hypogaea (groundnut), Avena sativa (oats), Capsicum frutescens (chilli), Citrullus lanatus (watermelon), Coffea arabica (arabica coffee), Cucumis sativus (cucumber), Cucurbita pepo (ornamental gourd), Daucus carota (carrot), Glycine max (soyabean), Gossypium hirsutum (Bourbon cotton), Hordeum vulgare (barley), Ipomoea batatas (sweet potato), Lycopersicon esculentum (tomato), Medicago sativa (lucerne), Musa (banana), Nicotiana tabacum (tobacco), Oryza sativa (rice), Passiflora edulis (passionfruit), Phaseolus vulgaris (common bean), Pisum sativum (pea), Prunus persica (peach), Vitis vinifera (grapevine), and Zea mays (maize).

Geographic distribution

Cosmopolitan

Biology and transmission

Not reported

Detection/indexing methods used at IITA

General methods for the detection of all nematodes

A:  On seeing suppressed growth/decreased production in crop plants

• Stage 1: Look for and assess symptoms of nematode damage
• Stage 2: Collect soil and plant tissue samples
• Stage 3: Extract nematodes from samples
• Stage 4: Identify nematodes  
• Stage 5: Nematode density assessment
• Stage 6: Nematode damage analysis
• Stage 7: Management decision

B :   Direct examination of plant material

• Wash the plant tissue/seed under a gentle stream of water, or place in a bowl of water for a few minutes, to remove soil and debris, taking care not to dislodge ectoparasitic nematodes feeding or attached on the outside of roots.
• Cut the plant tissue into ~2cm pieces with a pair of sharp scissors or knife.
• Place the plant tissue into an open Petri dish that has water in the base
• For immediate observation tease open the tissue with the aid of mounted needles and forceps to release the nematodes from the plant tissue. This is suitable for sedentary endoparasites.
• If the plant tissue contains migratory nematodes it may be useful to leave in a Petri dish overnight or longer even. Nematodes will migrate out of the tissue into the water.
• Nematodes can then be picked under the stereomicroscope for identification or preserved (and stained) and/or sent for further identification
• Infected materials are discarded by incineration

Treatment/control

• Plant resistant varieties.
• Crop rotation 2 yearly interval
• Use of nematicides as soil fumigants

Procedures in case of positive test at IITA

• Discard. Not acceptable for international distribution

References and further reading

Sasser JN, Carter CC. 1984. Overview of the International Meloidogyne Project, 1975-1984, pp. 19 - 24. In: Sasser JN, Carter CC, editors. An advanced treatise on Meloidogyne, Vol. 1 Biology and control. Raleigh, NC: A Cooperative Publication of the Department of Plant Pathology and Genetics, North Carolina State University, and the United States Agencey for International Development

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Reniform nematodes

Scientific name

Rotylenchulus reniformis

Other scientific names

Rotylenchulus leiperi (Das) Loof & Oostenbrunk, 1961
Rotylenchulus queirozi (Lordello & Cesnik) Sher, 1961
Rotylenchulus stakmani Husain & Khan, 196

Importance

High

Significance

The nematode is a pest of economic importance of cowpea , cotton, pineapple, sweet potato and soyabean, banana, aubergine, cabbage, okra, melon, pigeon pea, tea and tobacco.

There are no quantified reports on yield losses of cowpea due to attack by this nematode, although losses ranging from 9.5-17.4% and 40-60% due to attack by this nematode have been reported on cotton in India, and Egypt (Bridge, 1992; Robinson et. al., 1997).

Symptoms

Symptoms exhibited on all plant parts on:

Leaf : chlorosis

Seed/seedling : delayed emergence

Whole plant : stunted growth, wilting, collapse (Gaur and Perry, 1991).

Hosts

R. reniformis has a wide host. (Robinson et al., 1997) with major hosts such as: Vigna unguiculata (cowpea), Abelmoschus esculentus (okra), Ananas comosus (pineapple), Brassica oleracea var. capitata (cabbage), Cajanus cajan (pigeon pea), Carica papaya (papaw), Citrus , Cucumis melo (melon), Cucurbitaceae (cucurbits), Glycine max (soyabean), Gossypium (cotton), Gossypium hirsutum (Bourbon cotton), Ipomoea batatas (sweet potato), Lycopersicon esculentum (tomato), Musa (banana), Phaseolus (beans), Solanum melongena (aubergine), and some recorded minor hosts include: Arachis hypogaea (groundnut), Artocarpus altilis (breadfruit), Beta vulgaris (beetroot), Brassica oleracea (cabbages, cauliflowers), Solanum tuberosum (potato), Sorghum halepense (Johnson grass), Theobroma cacao (cocoa), triticum aestivum (wheat), Vicia faba (broad bean), Vigna mungo (black gram), Vigna radiata (mung bean), Vitis vinifera (grapevine), Xanthosoma sagittifolium ( Cocoyam),and Zea mays (maize).

Geographic distribution

R. reniformis is very widely distributed in the subtropical and tropical regions of the world and also in some warm temperate localities in Europe and other countries.

Biology and transmission

R. reniformis is a soil inhabiting semi-endoparasite of roots. (Robinson et. al., 1997). The life cycle from egg to egg can be as short as 3 weeks

The nematode has biological races. In India, the nematode is reported to have at least two races on the basis of parasitism on three hosts, one parasitic on cowpea, castor and cotton, the other parasitic only on cowpea.

Races have also reported from USA, Cuba and Japan (Dasgupta and Seshadri, 1971; Robinson et al., 1997.

Detection/indexing methods used at IITA

Direct examination of plant material

• Wash the plant tissue/seed under a gentle stream of water, or place in a bowl of water for a few minutes, to remove soil and debris, taking care not to dislodge ectoparasitic nematodes feeding or attached on the outside of roots.
• Cut the plant tissue into ~2cm pieces with a pair of sharp scissors or knife.
• Place the plant tissue into an open Petri dish that has water in the base
• For immediate observation tease open the tissue with the aid of mounted needles and forceps to release the nematodes from the plant tissue. This is suitable for sedentary endoparasites.
• If the plant tissue contains migratory nematodes it may be useful to leave in a Petri dish overnight or longer even. Nematodes will migrate out of the tissue into the water.
• Nematodes can then be picked under the stereomicroscope for identification or preserved (and staining the roots and nematodes in acid fuchsin or methyl blue and examining under a microscope.) and/or sent for further identification 

Treatment

• Plant resistant varieties
• Crop rotation 2 yearly interval
• Use of nematicides as soil fumigants

Procedures in case of positive test at IITA

• Discard. Not acceptable for international distribution
• Infected materials are discarded by incineration

References and further references

Bridge J. 1992. Nematodes. In: Hillocks RJ, editor. Cotton diseases, Wallingford, UK: CAB International, 331-353.

Dasgupta DR, Seshadri AR. 1971. Races of the reniform nematode, Rotylenchulus reniformis Linford and Oliveira, 1940. Indian Journal of Nematology, 1:21-24.

Gaur HS, Perry RN. 1991. The biology and control of the plant parasitic nematode Rotylenchulus reniformis. Agricultural Zoology Reviews, 4:177-212.

Robinson AF, Inserra RN, Caswell-Chen EP, Vovlas N, Troccoli A. 1997. Rotylenchulus species: identification, distribution, host ranges, and crop plant resistance. Nematropica, 27(2):127-180

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Fungi - cowpea

Contributors to this section: IITA, Nigeria (M. Ayodele, L. Kumar).

Contents: Anthracnose, Bean anthracnose Cercospora leaf spots, Leaf spot of cowpea Leaf spot of cowpea Fusarium wilt, Cowpea wilt Scab Brown blotch, Brown blotch of cowpea Rust, Bean rust Leaf smut, Black spot of pulses Septoria leaf spot Lamptail pod rot of cowpea, Blight of cowpea, Pod rot of cowpea

Anthracnose, Bean anthracnose

Scientific names

Colletotrichum lindemuthianum, Glomerella lindemuthiana Shear [teleomorph]

Other scientific names

Gloeosporium lindemuthianum Sacc., Gloeosporium socium Sacc.

Importance

High

Significance

Anthracnose affects yield, seed quality and marketability of the crop. The disease causes huge losses in temperate and subtropical zones. Losses of 35,925 tonnes due to anthracnose have been estimated in Rwanda. (Tu, 1988). Yield losses of 95% have been recorded in Colombia and over 92% in Malawi (Allen, 1983). In East Africa, anthracnose is important in Kenya, Uganda and Tanzania. It is recurrent in the Great Lakes Region of Rwanda, Burundi and the Kivu Province of Zaire (CIAT, 1981).
In South America, it had been reported that C. lindemuthianum caused severe damage in Brazil (Vieira, 1983), Argentina (Ploper, 1983), Mexico (Crispin-Medina and Campos-Avila, 1976), Guatemala, Costa Rica, Nicaragua (Echandi, 1976), Peru, Ecuador, and Colombia (Olarte et al., 1981.

Symptoms

The fungus infects all stages of the plant, flowering , podding, pre-emergence, seedling and vegetative growing stages and all plant parts including the pods, leaves and seeds. Initial symptoms may appear on cotyledonary leaves as small, dark brown to black lesions.The infected tissues manifest minute rust-coloured specks. The specks gradually enlarge longitudinally and form sunken lesions or eye-spots.

Leaves: lesions first develop on leaf petioles, the lower surface of leaves and leaf veins as small, angular, brick-red to purple spots which become dark brown to black. Later, the lesions may also appear on veinlets on the upper surface of leaves.

Seedlings: lesions enlarge on the hypocotyl of the young seedling, causing rot.

Stem: eye-shaped lesion develop.

Pod: infections appear as rusty brown spots with small, brown specks, sunken cankers delimited by a slightly raised black ring and surrounded by a reddish-brown border. young pods shrivel and dry up.

Seed: discolouration, dark brown to black cankers, brown to light chocolate spots on the seed coats.

C. lindemuthianum (photo: IITA)

Hosts

The major hosts infected by this fungus are Vigna unguiculata (cowpea), Cajanus cajan (pigeon pea), Lablab purpureus (hyacinth bean), Phaseolus (beans), Phaseolus vulgaris (common bean), Vigna sinensis ssp. sesquipedalis (asparagus bean.

The minor hosts include Glycine max (soyabean), Lens culinaris ssp. culinaris (lentil), Phaseolus coccineus (runner bean), Pisum sativum (pea), Vicia faba (broad bean), Vigna mungo (black gram), Vigna radiata (mung bean), and Canavalia ensiformis (gotani bean.

Geographic distribution

Worldwide

Biology and transmission

Conidia which are round or elongated are borne on acervuli which may be present on pods, leaves, stems and branches.  The mycelium is hyaline, branched and septate.

A conidium takes 6-9 hours to germinate under favourable environmental conditions. The pathogen penetrates the cuticle and epidermis mechanically (Leach, 1923). Following penetration of host cells, when temperatures are favorable, infectious hyphae enlarge and grow between the cell wall and protoplast for 2-4 days without apparent damage to host cells ).
C.  lindemuthianum is seed borne and seed transmitted.

C. Lindemuthianum has various strains classified on the basis of host reaction.Two distinct races have been characterized as alpha and beta. Several new races have been identified in Canada, USA, Europe, Brazil and Africa.

Mordue, (1971a,b) reported that the fungus can survive for at least 2 years in seed. The longevity in infected pods and seeds varies considerably depending on environmental conditions. The pathogen was able to survive for at least 5 years on pods and seeds that were air-dried and kept in storage at 4°C or on dry, infected plant materials left in the field in sealed polyethylene envelopes (Tu, 1983).

C. lindemuthianum survives as dormant mycelium within the seed coat, sometimes even within cells of cotyledons, as spores between cotyledons or elsewhere in the seed (Zaumeyer and Meiners, 1975). The fungus survives in the seed as long as the seed remains viable It also survives in infected crop residues.

Infection is favoured by moderate temperatures between 13 and 26°C; (Ferrante and Bisiach, 1976), while Tu and Aylesworth, (1980) reported that infection is favoured by an optimum temparature of 17-24°C.

Humidity of more than 92% or free moisture is required during all stages of conidium germination, incubation and subsequent sporulation; (Tu, 1982).

Zaumeyer and Thomas, (1957) reported that the dissemination and spread of the conidia, and the development of severe anthracnose epidemics is favoured by wind or rain. C. lindemuthianum required about 10 mm of rain to establish infection (Tu, 1981).   Conidia spread may be   dispersed within the crop by insects, animals and man, especially when foliage is moist (Zaumeyer and Thomas, 1957).

Detection/indexing methods used at IITA

• Agar method. The Nutrient Broth Yeast extract (NBY) agar medium is used for the detection of the pathogen 

• According to ISTA randomly select a sub sample of 500 seeds (or less if fewer seeds are available) from the seed lot.
• Surface disinfection of seeds using 10% Sodium hypochlorite for 3 minutes.
• Rinse the seed in sterile distilled water and blot off excess.
• Plate the material on NBY agar medium and incubate at 28^oC for 4days.
• Examine plate under stereo microscope.
• Make microscopic slides of fungal fruiting bodies observed in growth.
• Examine under compound microscope to identify the fungal fruiting bodies and spores isolated from the mycelial growth
• Subculture on NBY to obtain pure cultures of the pathogen for pathogenicity tests/ preservation
• Make microscopic slides of the spores and re examine under the Compound microscope for confirmation and purity.

Treatment/cControl

• Seed treatment with mancozeb(Ethylene Bisdithiocarbamate ) 80g a.i./kg of seeds
• Plant pathogen free healthy resistant varieties. IITA has bred several resistant lines
• Production of seeds for export in Certified Pest Free areas (PFA)
• Fungicidal field sprays in the field during active growth

Procedures in case of positive test at IITA

• Seeds from lines testing positive are treated with mancozeb 80g/kg of seeds. The treated seeds are retested after 3 days. If the pathogen is isolated from the treated lines, the lines are rejected. Not for international distribution in compliance to the importing countries’ phytosanitary regulations.

References and further reading

Allen DJ. 1983. The pathology of tropical food legumes: disease resistance in crop improvement. Chichester, UK: John Wiley & Sons

CAB International. 2007. Crop Protection Compendium, 2007 Edition. Wallingford, UK: CAB International

CIAT. 1981. Potential for field beans in eastern Africa: proceedings of a regional workshop held in Lilongwe, Malawi, 9-14 March 1980. CIAT Series 03EB-1. Cali, Colombia: CIAT.

Crispin A, Campos J. 1976. Bean diseases of importance in Mexico in 1975. Plant Disease Reporter, 60(6):534-535.

Echandi E. 1976. Principal fungus diseases of bean (Phaseolus vulgaris) in the American tropics in different ecological zones. Fitopatologia Brasileira, 1(3):171-177

Ferrante GM, Bisiach M. 1976. Comparison of methods for experimental infection of bean with Colletotrichum lindemuthianum. Rivista di Patologia Vegetale, IV, 12(3/4):99-118;

Leach JG. 1923. The parasitism of Colletotrichum lindemuthianum. Minnesota Agricultural Experiment Station Technical Bulletin, 14.

Mordue JEM. 1971a. Colletotrichum lindemuthianum. Descriptions of Pathogenic Fungi and Bacteria Set 32, Sheet No. 316. Wallingford, UK: CAB International.

Mordue JEM. 1971. Glomerella cingulata. CMI Descriptions of Pathogenic Fungi & Bacteria No. 315. Wallingford, UK: CAB International.

Olarte MD, Osorio G, Puerta OD, Isaza L. 1981. Mechanisms for primary infection by anthracnose (Colletotrichum lindemuthianum) on bean (Phaseolus vulgaris) in Eastern Antioch. Fitopatologia Colombiana, 10(1/2):23-28;

Ploper LD. 1983. Bean diseases in Northwest Argentina and their control. Publicación Miscelánea Estación Experimental Agro-Industrial "Obispo Colombres" de Tucumán, No.74:87-103;

Olarte MD, Osorio G, Puerta OD, Isaza L. 1981. Mechanisms for primary infection by anthracnose (Colletotrichum lindemuthianum) on bean (Phaseolus vulgaris) in Eastern Antioch. Fitopatologia Colombiana, 10(1/2):23-28;

Tu JC. 1981. Anthracnose (Colletotrichum lindemuthianum) on white bean (Phaseolus vulgaris L.) in southern Ontario: spread of the disease from an infection focus. Plant Disease, 65(6):477-480

Tu JC. 1982. Effect of temperature on incidence and severity of anthracnose on white bean. Plant Disease, 66(9):781-783;

Tu JC. 1983. Epidemiology of anthracnose caused by Colletotrichum lindemuthianum on white bean (Phaseolus vulgaris) in southern Ontario: survival of the pathogen. Plant Disease, 67(4):402-404

Tu JC. 1988. Control of bean anthracnose caused by the delta and lambda races of Colletotrichum lindemuthianum in Canada. Plant Disease, 72(1):5-8.

Tu JC, Aylesworth JW. 1980. An effective method of screening white (pea) bean seedlings (Phaseolus vulgaris L.) for resistance to Colletotrichum lindemuthianum. Phytopathologische Zeitschrift, 99(2):131-137;

Zaumeyer WJ, Meiners JP. 1975. Disease resistance in beans. Annual Review of Phytopathology, 13:313-334.

Zaumeyer WJ, Thomas HR. 1957. A monographic study of bean diseases and methods for their control. United States Department of Agricultural Technical Bulletin, 868

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Cercospora leaf spots, Leaf spot of cowpea

Scientific name

Cercospora canescens

Other scientific name

Cercospora vignicaulis Tehon

Importance

High

Significance

Yield loss due to seed infection has not been quantified

Symptoms

The symptoms are prominent on the leaves alone. However, the fungus has been isolated from infected seeds which are symptomless. Symptoms found on various plant parts are as follows:

Leaves: subcircular to broadly irregular spots having pale tan to grey centre surrounded by dark brown or reddish margin. The spots coalesce to form round lesions which are brown and necrotic with dark, and slightly depressed edges.
 

Pods: damaged pods, drying up.

Stem: lesions on the stem, and cotyledons 

Hosts

Although the disease occurs mainly on cowpeas and on grain legumes, other major and minor hosts have been identified.

The major hosts are Vigna unguiculata (cowpea), Amaranthus (grain amaranth), Glycine max( soybean) , Lablab purpureus (hyacinth bean), Lycopersicon esculentum (tomato), Phaseolus (beans), Ricinus , Vicia (vetch), Vigna (cowpea), Voandzeia subterranea (bambara groundnut).

Other hosts obtained from artificial inoculations are :
Crotalaria juncea (sunn hemp), Psophocarpus tetragonolobus, (winged bean), Vigna angularis (adzuki bean), Vigna mungo (black gram) and Vigna radiata (mung bean).

Geographic distribution

The disease is widespread in warmer subtropical and tropical regions. The fungus has been reported in the Eastern region of USA (Farr et al., 1989); Bangladesh, China, India, Indonesia, Thailand, Africa, Brazil and Samoa.

Biology and transmission

Abundant fruiting bodies on the lower surface of the leaf. The conidia are uniform in colour, pale to medium brown, multiseptate, medium to large size, conidial scar present on the rounded apex, thickened hilum. Most conidia are formed at 28°C, while at 24°C and 32°C less conidia are formed. The presence of light increases the number of conidia (Mulder and Holliday, 1975).

Detection/indexing methods used at IITA

Blotter method.

Procedure

According to ISTA, randomly select a sub sample of 500 seeds (or less if fewer seeds are available) from the seed lot.

• Surface disinfection of seeds using 10% Sodium hypochlorite for 3 minutes.
• Rinse the seed in sterile distilled water and blot off excess.
• Plate the material on blotter and incubate at 28^oC for 4days.
• Examine plate under stereo microscope.
• Make microscopic slides of fungal fruiting bodies observed in growth.
• Examine under compound microscope to identify the fungal fruiting bodies and spores
• isolated from the mycelial growth
• Subculture on NBY to obtain pure cultures of the pathogen .
• Make microscopic slides of the spores and re examine under the compound microscope
• for confirmation and purity. Pick single spores and transfer unto V8 agar for sporulation

(The V8 juice agar contains: 3.0 g of calcium carbonate (CaCO₃),2.5 g of glucose 20 g of agar powder, 200 ml of V8 juice adjust to 1 litre and autoclave, cool to about 40⁰C. Add 1g of streptomycin powder to prevent bacterial growth).

• Incubate for 2 days at 27^oC. Reexamine for purity. For preservation subculture unto ¼ strength PDA slants. Incubation beyond 3 days causes the spores to collapse.

Treatment/control

• Seed treatment with mancozeb ( Ethylene Bisdithiocarbamate ) 80g/kg of seeds
• Plant pathogen free healthy resistant varieties. IITA has bred several resistant lines.
• Production of seeds for export in Certified Pest Free areas(PFA)
• Fungicidal field sprays in the field during active growth

Procedures in case of positive test at IITA

• Seed treatment with mancozeb 80g/kg of seeds. The treated lines to be retested after 3 days of treatment. If the pathogen is isolated from the treated lines, the lines are rejected. Not for international distribution in compliance to the importing countries’ phytosanitary regulations.

References and further reading

CAB International. 2007. Crop Protection Compendium, 2007 Edition. Wallingford, UK: CAB International.

Farr DF, Bills GF, Chamuris GP, Rossman AY. 1989. Fungi on plants and plant products in the United States. St. Paul, Minnesota, USA: APS Press

Mulder JL, Holliday P. 1975. Cercospora canescens. CMI Descriptions of Pathogenic Fungi and Bacteria, No. 462. Wallingford, UK: CAB International.

Field symptom (photo:IITA)

growth on agar (photo:IITA)

conidia (photo:IITA)

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Leaf spot of cowpea

Scientific name

Cercospora cruenta; Mycosphaerella cruenta Latham [Teleomorph].

Other scientific name

Pseudocercospora cruenta (Sacc.) Deighton

Importance

High

Significance

Fery et al., (1977) reported that M. cruenta reduced the number of pods per plant and the number of seeds per pod. This Cercospora leaf spot disease has been reported by Williams, (1977) to have caused considerable yield losses in cowpea fields in Nigeria.
Schwartz and Pastor-Corrales, (1989) in a study in USA, reported that M. cruenta leaf spot of cowpea reduced the seed yield of the susceptible cv. Colossus by 35.6% . While in Varanasi, India, leaf spot caused by M. cruenta was found to cause serious disease in lobiya (Vigna unguiculata) (Pant, 1989).

Symptoms

The fungus infects the pods, leaves and stems showing various symptoms such as:

Leaves: brown or rust-coloured circular to angular spots, coalesce forming lesions, chlorosis, abnormal leaf fall, and fungal growth on the leaves

Stems: Lesions, discoloration on branches,

Pods: lesions, discoloration 

Seed: poor to no germination,small and abnormal

Whole plant: abnormal growth and development.

Hosts

The major hosts for this pathogen are Vigna unguiculata (cowpea), Phaseolus (beans), ) while some recorded minor hosts are Calopogonium, Lablab purpureus (hyacinth bean), Mucuna (velvetbeans), and Mucuna pruriens (Buffalobean).

Geographic distribution

Cosmopolitan

Biology and transmission

The perfect stage produce colourless, 1-septate, ascospores with upper cell which sometimes are slightly larger than the lower cell, straight to slightly curved,

Microconidia are rod-shaped, hyaline, aseptate, produced in pycnidia in or near lesions formed by the imperfect stage, Cercospora. The conidia are thin-walled, filiform, smooth, and hyaline to olivaceous-brown, 4-9-septate. M. cruenta survives between growing seasons on crop residues, diseased leaf and stem crop residues of cowpea (Vigna unguiculata).

The disease is seed borne and seed transmitted

Detection/indexing methods used at IITA

Blotter method.

Procedure

• According to ISTA, randomly select a sub sample of 500 seeds (or less if fewer seeds are available) from the seed lot.
• Surface disinfection of seeds using 10% Sodium hypochlorite for 3 minutes.
•  Rinse the seed in sterile distilled water and blot off excess.
• Plate the material on blotter and incubate at 28^oC for 4days.
• Examine plate under stereo microscope.
• Make microscopic slides of fungal fruiting bodies observed in growth.
• Examine under compound microscope to identify the fungal fruiting bodies and spores isolated from the mycelial growth.
• Subculture on NBY to obtain pure cultures of the pathogen .
• Make microscopic slides of the spores and re examine under the compound microscope for confirmation and purity. Pick single spores and transfer unto V8 agar for sporulation
• Incubate for 2 days at 27^oC. Reexamine for purity. For preservation subculture unto ¼ strength PDA slants

Treatment/control

• Use resistant varieties available in IITA
• Seed treatment with mancozeb( Ethylene Bisdithiocarbamate ) 80g/kg of seeds
• Plant pathogen free healthy resistant varieties.
• Production of seeds for export in Certified Pest Free areas(PFA)
• Fungicidal field sprays in the field during active growth.

Procedures in case of positive test at IITA

• Seed treatment with mancozeb 80g/kg of seeds. The treated lines to be retested after 3 days of treatment. If the pathogen is isolated from the treated lines, the lines are rejected. Not for international distribution in compliance to the importing countries’ phytosanitary regulations.

References

CAB International. 2007. Crop Protection Compendium, 2007 Edition. Wallingford, UK: CAB International

Fery RL, Dukes PD. 1977a. Cercospora leaf spot of southernpea: studies on yield-loss and genetics of resistance. HortScience, 12(3):234.

Pant DC. 1989. Perpetuation of leaf spot organism of lobiya. Indian Phytopathology, 42(1):187-188.

Schwartz HF, Pastor-Corrales MA. 1989. Bean production problems in the tropics, 2nd edition. Cali, Colombia: CIAT

Williams RJ. 1977. Identification of multiple disease resistance in cowpea. Tropical Agriculture, 54(1):53-59.

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Fusarium wilt, Cowpea wilt

Scientific name

Fusarium oxysporum f.sp. tracheiphilum (E.F.Sm.) Snyder & H.N. Hansen

Other scientific names

Fusarium bulbigenum var. tracheiphilum, E.F. Sm. Wollenw
Fusarium tracheiphilum E.F. Sm.
Fusarium bulbigenum Cooke & Massee

Importance

High

Significance

Toler et al. (1963) reported that Fusarium wilt of cowpea caused by F. oxysporum f.sp. tracheiphilum is a destructive disease in the Southern and Eastern USA . In India, the yield loss caused by the fungus was 26.8-64.5% in 1954 (Singh, 1954) and 74.6% in 1955 (Singh and Sinha, 1955). And in 1996, the wilt incidence in India was recorded as 30% by Ushamalini (1996).

Symptoms

Fusarium oxysporum f. sp. tracheiphilum attacks young and old plants. Symptoms of the disease are visible on leaves, stem and roots. The vascular bundles show brownish-black discoloration. All plant parts are affected and showing different symptoms such as on:

Leaves: yellowing, withering, Chlorosis, leaf drooping,

Shoots: dry and naked 

Stem: blackened and swollen, wilt (Singh and Sinha, 1955

Pods: presence of pinkish-white fungal growth

Seeds: discoloration, shrivelling, ashy white and shrunken (Ushamalini, 1996)

Roots: rot; reduced root system; absence of lateral roots , lesions

Whole plant: systemic infection, colonization of xylem vessels resulting   in chlorosis, die back, dwarfing.

Hosts

The major hosts of this pathogen are:
Vigna unguiculata (cowpea) and some minor hosts such as Chrysanthemum vestitum Glycine max (soyabean), and Phaseolus vulgaris (common bean).

Geographic distribution

Cosmopolitan

Biology and transmission

Morphology of F. oxysporum f.sp. tracheiphilum on oat meal agar, has a cotton wool appearance, with a white to purple aerial mycelium. The microconidia are ellipsoidal, hyaline, and aseptate . The macroconidia are slightly curved, mostly septate. The chlamydospores are ellipsoidal to globose, terminal or intercalary and aseptate. The fungus also produces small, abundant sporodochia on PDA in 8-12 days at 26-30°C.The symptoms of vascular wilt are severe at higher temperatures of 27°C (Swanson and Van Gundy, 1985). Swanson, (1984). Harris and Ferris, (1991b) further reported that the wilt symptom is very severe when the fungus is in association with the nematode , Meloidogyne javanica . F. oxysporum f. sp. tracheiphilum is seed borne and seed transmitted. Seeds from wilted plants stored in the refrigerator for 4 years remained viable (Armstrong and Armstrong, 1950). The fungus was found to be present in the seed coat, cotyledon, and embryo.

Detection/indexing methods used at IITA

Agar method 

Procedure

• Randomly select a sub sample of 500 seeds (or less if fewer seeds are available) from the seed lot. Surface disinfection of seeds using 10% Sodium hypochlorite for 3 minutes.
• Rince the seed in sterile distilled water and blot off excess.
• Plate the material on NBY agar medium and incubate at 28^oC for 4days.
• Examine plate under stereo microscope.
• Make microscopic slides of fungal fruiting bodies observed in growth.
• Examine under compound microscope to identify the fungal fruiting bodies and spores isolated from the mycelial growth
• Subculture on PDA to obtain pure cultures of the pathogen for pathogenicity tests/ preservation
• Make microscopic slides of the spores and re examine under the Compound microscope for confirmation and purity. 

Treatment/control

• Use resistant varieties. Available at  IITA.
• Seed treatment with mancozeb( Ethylene Bisdithiocarbamate ) 80g/kg of seeds
• Plant pathogen free healthy resistant varieties.
• Production of seeds for export in Certified Pest Free areas(PFA)
• Growing on test in the screen house, active growth inspection, wilted plants rogued and incinerated

Procedures in case of positive test at IITA

• Seed treatment with mancozeb 80g/kg of seeds. The treated lines to be retested after 3 days of treatment. If the pathogen is isolated from the treated lines, the lines are rejected. Not for international distribution in compliance to the importing countries’ phytosanitary regulations.

For import or export:

• For valuable germplasm material to be used for crossing by breeders, growing on test in the containment , active growth inspection, wilted plants rogued and incinerated
• Seeds from symptomless plants harvested and retested before release for use.

References and further reading

Armstrong GM, Armstrong JK. 1950. Biological races of the Fusarium causing wilt of cowpeas and soybeans. Phytopathology, 40:181-193

Harris AR, Ferris H. 1991. Interactions between Fusarium oxysporum f.sp. tracheiphilum and Meloidogyne spp. in Vigna unguiculata. 1. Effects of different inoculum densities on Fusarium wilt. Plant Pathology, 40(3):445-456.

ISTA. 1985. International rules for seed testing. Seed Science and Technology, 13:484-487.

Singh RS, Sinha RP. 1955. Studies on the wilt disease of cowpea in Uttar Pradesh. J. Indian Bot. Soc., 34:375-381.

Swanson TA. 1984. Root-knot nematode and Fusarium wilt diseases of cowpea and soybean. PhD. thesis University of California, Riverside.

Swanson TA, Gundy SDVan. 1985. Influences of temperature and plant age on differentiation of races of Fusarium oxysporum f.sp. tracheiphilum on cowpea. Plant Disease, 69(9):779-781;

Thomason IJ, Erwin DC, Garder MJ. 1959. The relationship of the root-knot nematode, Meloidogyne javanica to Fusarium Wilt of Cowpea. Phytopathology, 49:602-606.

clean seeds (photo:IITA)

infected seeds (photo:IITA)

growth on agar (photo:IITA)

conidia (photo:IITA)

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Scab

Scientific name

Sphaceloma sp.

Other scientific names

Elsinoe phaseoli,Jenkins ; Elsinoe vignicola

Importance

High

Significance

High.

Serious disease causing loss of foliage, pods and seeds. In severe case there is complete loss of yield. Exact yield loss caused by this fungus has not been quantified.

The disease is endemic in Zaria, Northern Nigeria.

Symptoms

The fungus attacks the stem, leaves, and pods of Vigna unguiculata

Symptoms on the different parts such as on :

Leaves: spots on both leaf surfaces, cupped. Appearance of small grayish scab lesion along the veins. Leaf distortion, Ragged appearance

Stems: oval to elongated silver grey lesions surrounded by red or brown   elliptical ring. Lesions coalesce, distortion

Pod: sunkened spots with grey centers surrounded by brown borders , malformation, dark coloured pycnidia formed in the brown spots.

Hosts

Vigna unguiculata, ( Cowpea) and Lima beans, Beans.

Geographic distribution

The disease has been reported in West and East Africa, Central America and severe outbreaks have been reported in Surinam ( Singh, S R and Allen D. J (1979).

Biology and transmission

The mycelium is hyaline, scanty and submerged. Conidia are hyaline to pale coloured. The conidia are produced in pycnidia. The ascospores borne on the asci are hyaline, pale colored oblong to elliptical, and 3 septate.

Detection/indexing methods used at IITA

• Collect infected plant parts ( stem, leaf, pods and seeds) from the field
• Prepare PDA+streptomycin and rose bengal
• Cowpea Pod Agar amended with PDA adding Streptomycin sulphate   (1.5g l^-1)
• And Rose Bengal (0.0025g l^-1)
• Cut the different infected parts into small portions
• Surface sterilize in 10% sodium hypochlorite for 3 minutes
• Blot with sterile paper towel
• Place five portions in each plate on the medium
• Incubate the plate at 27c for 5-7 days
• Examine under microscope. 

Treatment/control

• Use resistant varieties. Available at IITA.
• Seed treatment with mancozeb( Ethylene Bisdithiocarbamate ) 80g/kg of seeds
• Plant pathogen free healthy resistant varieties.
• Production of seeds for export in Certified Pest Free areas(PFA) 

Procedures in case of positive test at IITA

• Seed treatment with mancozeb 80g/kg of seeds. The treated lines to be retested after 3 days. If the pathogen is isolated from the treated lines, the lines are rejected. Not for international distribution in compliance to the importing countries’ phytosanitary  regulations
• For import or export:
• For valuable germplasm material to be used for crossing, growing on test in the containment , active growth inspection is conducted. Plants with scab symptoms are rogued and incinerated
• Seeds from symptomless plants harvested and retested for freedom from fungus. 

References and further reading

Singh SR, Allen DJ. 1979. Cowpea pests and Diseases. IITA monograph. Manual series No 2. Trop. Grain Legume Entomology, IITA, Ibadan, Nigerial.

Pod and stem scab (photo:IITA)

Pod and stem scab (photo:IITA)

Stem scab (photo:IITA)

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Brown blotch, Brown blotch of cowpea

Scientific name

Colletotrichum truncatum(Schwein.) Andrus & W.D. Moore, 1934

Other scientific names

Colletotrichum dematium f. truncatum, (Schwein.) Arx
Vermicularia  truncata Schwein. 1832

Importance

High

Significance

 Rheenen, (1975) attributed yield losses of 30% to anthracnose infection in Nigeria. A survey conducted in two states in Brazil detected the disease in 57% of the fields (Lehman et al., 1976). Anthracnose of maturing plants causes serious losses, particularly during the rainy period when shaded lower branches and leaves die due to severe infection. 

Symptoms

C.truncatum affects all plant stages and parts - flowering , podding, seedling stages also the pods, inflorescence, leaves, stems and whole plant. The stems, pods and leaves may be infected without showing symptoms. In the advanced stages of anthracnose in the late reproductive stages, infected tissues are covered with black fruiting bodies (conidiomata) which produce setae (minute black spines).
Symptoms found on the different plant parts such as on the:

• Inflorescence: lesions.
• >Leaves: lesions; abnormal colours and forms; fungal growth, necrosis of laminar veins, leaf rolling and petiole cankers. Premature defoliation, girdling of the leaf and petiole Developpment of shepherd's crook .
• Seedlings: discoloration; canker, premature death, and severe reductions in seedling emergence was recorded by Athow, (1987).
• Pods: lesions. irregularly-shaped, brown areas , blanking( no pod formation), reduction in pod size and number.
• Seeds: small, irregular, grey areas with black specks, brown staining, symptomless. The fungus is confined at first to the seed coat. The infected seeds may die during germination or, if they germinate, produce infected seedlings.
• Whole plant: damping off; dwarfing, early senescens.

Hosts

C. truncatum has a wide host range among the local edible legumes. The fungus attacks crops considered as major and minor hosts. The major hosts are Vigna unguiculata (cowpea), Arachis hypogaea (groundnut), Cajanus cajan (pigeon pea), Capsicum annuum (bell pepper), Centrosema , Centrosema pubescens (Centro), Glycine max (soyabean), Medicago sativa (lucerne), Phaseolus (beans), Phaseolus lunatus (lima bean), Phaseolus vulgaris (common bean), Pisum sativum (pea), Vigna (cowpea), Vigna mungo (black gram), Vigna radiata (mung bean).

In addition to the host species mentioned above, C. truncatum has been isolated from several weed species (Hartman et al., 1986; Roy, 1982).

Geographic distribution

Cosmopolitan

Biology and transmission

The hyphae are hyaline, branched and septate

C. truncatum has crowded, black acervuli which are borne on well-developed stromata. It produces numerous, black mixed setae in culture, some are long and others short.

The conidia are borne singly on conidiophores, bluntly tapered, curved, unicellular, and hyaline. Conidia produce one or two short germ tubes which produce dark, sticky appressoria when in contact with the surface of the host plant

The disease is seed borne and seed transmitted .

Detection/indexing methods used at IITA

Seed Health Tests

• Agar method The Nutrient Broth Yeast extract (NBY) agar medium is used for the detection of the pathogen. 

Procedure

• Randomly select a sub sample of 500 seeds (or less if fewer seeds are available) from the seed lot.
• Surface disinfection of seeds using 10% Sodium hypochlorite for 3 minutes.
• Rince the seed in sterile distilled water and blot off excess.
• Plate the material on NBY agar medium/ Blotter and incubate at 28^oC for 4days.
• Examine plate under stereo microscope.
• Make microscopic slides of fungal fruiting bodies observed in growth.
• Examine under compound microscope to identify the fungal fruiting bodies and spores isolated from the mycelial growth
• Subculture on NBY to obtain pure cultures of the pathogen for pathogenicity / preservation
• Make microscopic slides of the spores and re examine under the compound microscope for confirmation and purity.

Treatment/control

• Seed Treatments with mancozeb followed by 2 foliar sprays of mancozeb.

Procedures in case of positive test at IITA

• Seed treatment with mancozeb 80g/kg of seeds. The treated lines to be retested after 3 days. If the pathogen is isolated from the treated lines, the lines are rejected. Not for international distribution in compliance to the importing countries’ phytosanitary regulations
• For import or export: for valuable germplasm material to be used for crossing, growing on test in the containment , active growth inspection is conducted. Plants with anthracnose symptoms are rogued and incinerated
• Seeds from symptomless plants harvested and retested

References and further reading

Athow KL. 1987. Fungal diseases. In: Wilcox JR, editor. Soybeans: Improvement, Production and Uses, 2nd edition, Monogr. 16. Madison, USA: American Society of Agronomy, 687-727.

Hartman GL, Manandhar JB, Sinclair JB. 1986. Incidence of Colletotrichum spp. on soybeans and weeds in Illinois and pathogenicity of Colletotrichum truncatum.. Plant Disease, 70(8):780-782

Lehman PS, Machado CC, Tarrago MT. 1976. Frequency and severity of soybean diseases in the States of Rio Grande do Sul and Santa Catarina. Fitopatologia Brasileira, 1(3):183-193

Rheenen HA. 1975. Soybeans in the northern states of Nigeria. In: Luse RA, Rachie KO, editors. Proceedings of IITA Collaborators Meeting on Grain Legume Improvement. Ibadan, Nigeria: IITA, 158-159.

Pod symptom (photo:IITA)

Growth on agar (photo:IITA)

Conidia and setae (photo:IITA)

Clean seeds (photo:IITA)

Infected seeds (photo:IITA)

Conidia (photo:IITA)

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Rust, Bean rust

Scientific name

Uromyces appendiculatus(Pers.) Unger (1816)

Other scientific names

Uromyces appendiculatus, Uromyces phaseoli,
Uromyces phaseolorum (DC.) de Bary,
Puccinia phaseoli-trilobi Schwein (1834),
Uromyces vignae-luteolae Henn.(1907).

Importance

High

Significance

Infection at the early stages of plant growth , results to crop failure. Yield losses reaching 28-54, 8-33 and 13-29% on different cultivars were reported by Gonzalez and Garcia (1996).

Symptoms

All plant parts above the ground are susceptible to infection. Infection appears at all stages of the plant growth.

• On the Leaves: yellow to yellowish-brown small raised blister like spots, as infection progresses, the blisters erupt and powder like uredo spores are exposed. The spores reinfect the plant and defoliation resulting to death of the plant.
• Stem: brown spots, spores and hyphae are borne internally and externally, spores visible to the eye
• Pods: brown spots, decrease in the number of pods per plant.
• Seed: malformation, decrease in weight of seed , sometimes symptomless

Hosts

The major hosts for the rust fungi are Vigna unguiculata (cowpea), Cajanus cajan (pigeon pea), Glycine max (soyabean), Lablab purpureus (hyacinth bean), Phaseolus (beans), Phaseolus lunatus (lima bean), Phaseolus vulgaris (common bean), Vigna angularis (adzuki bean), Vigna mungo (black gram) and some recorded minor hosts are Phaseolus coccineus (runner bean), Vigna radiata (mung bean), Vigna umbellata (Rice- bean), Voandzeia subterranea (bambara groundnut.

Geographic distribution

Rust is a universal disease of beans and is world wide in spread and distribution.

Biology and transmission

The mycelium is hyaline, branched and septate existing internally in host tissue producing various sori . It is autoecious having white pycnidia in small groups. Aecia are very rare but the aeciospores are globose to ellipsoid. Uredinia , sometimes absent but if present are pale brown, solitary or sometimes aggregated, minute,and cinnamon brown. Urediniospores are globose to subglobose.

Telia are blackish-brown to black. The teliospores are subglobose to ovoid or ellipsoid and rounded at the apex.

There can be crop failure if infection takes place in the early stages of plant growth. Overcast conditions and a temperature of 20-25ºC favour the pathogen. Twenty races of the pathogen were reported by Staveley (1984a) when he used 19 different bean cultivars in an experiment in USA.

Detection/indexing methods used at IITA .

• Two methods are used for isolation of the pathogen. Seed washing method and leaf isolation.

Seed washing method

• Randomly select a sub sample of 500 seeds (or less if fewer seeds are available) from the seed lot and place in a 250-ml flask.
• Add 100 ml of water and 5 drops of tween 80. Shake vigorously for 30 sec.
• Pour 10 ml of the resulting suspension into a test tube and centrifuge in table-top centrifuge for 5 minutes at 4000 rpm.
• Pour off the supernatant and resuspend the pellet in the bit of remaining water by tapping the tube with your finger. Place of a drop of the suspension on a microscope slide, cover with a cover slip, and inspect the entire slide at X10 and above under the compound microscope.
• Look for spores, fruiting bodies. Identify

Leaf isolation method/Slide

• Collect infected leaf sample from the field.
• Harvest Uromyces appendiculatus spores from infected samples using a needle on to a clean slide.
• Add a drop of lactophenol or cotton blue
• View under microscope to check for uredospores

Treatment/control

• Seed treatment with mancozeb followed by field spray before flowering reduced infection but did not eradicate the pathogen
• Plant resistant varieties
• Use disease free seeds and multiply seeds in PFAs

Procedures in case of positive test

• Discard. Not for international distribution in compliance to the importing countries’ phytosanitary regulations
• For import or export: For important germplasm material to be used for crossing, growing on test in the containment , active growth inspection, plants with rust symptoms are rogued and incinerated
• Seeds from symptomless plants harvested and retested

References and further reading

Gonzalez M, Garcia E. 1996. Evaluation of losses due to the rust on bean (Phaseolus vulgaris L.) in four sowing times in Cuba. Agronomia Mesoamericana, 7:95-98.

Stavely JR. 1984. Genetics of resistance to Uromyces phaseoli in a Phaseolus vulgaris line resistant to most races of the pathogen. Phytopathology, 74(3):339-344;

Staveley JR. 1984b. Pathogenic specialization in Uromyces phaseoli in the United States and rust resistance in beans. Plant Disease, 68:95-99.

Infected leaf (photo:IITA)

Infected leaf (photo:IITA)

Uredospores (photo:IITA)

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Leaf smut, Black spot of pulses

Scientific name

Entyloma vignae

Other scientific name

Protomycopsis phaseoli

Importance

High

Significance

The disease is of economic importance in Brazil where yield losses of 30-40% were reported.

Symptoms

The symptoms are very prominent on the leaves.

Leaves: dark ash grey to black, circular, purplish spots surrounded by yellow hallow border. As infection progresses, spots coalesce, become dark purple leaves become ragged and fall off.

Whole plant: severe infection causes defoliation

Hosts

The only listed hosts are Vigna unguiculata ,(cowpea), Lablab purpureus ,and (hyacinth bean)Vigna radiata (mung bean).

Geographic distribution

India, Africa, Jamaica, Brazil

Biology and transmission

Chlamydospores are black and spherical. Germination by formation of basidia.
Concomitant contamination of seeds.

Detection/indexing methods used at IITA

Seed washing method

• Randomly select a sub sample of 500 seeds (or less if fewer seeds are available) from the seed lot and place in a 250-ml flask.
• Add 100 ml of water and 5 drops of tween 80. Shake vigorously for 30 sec.
• Pour 10 ml of the resulting suspension into a test tube and centrifuge in table-top centrifuge for 5 minutes at 4000 rpm.
• Pour off the supernatant and resuspend the pellet in the bit of remaining water by tapping the tube with your finger. Place of a drop of the suspension on a microscope slide, cover with a cover slip, and inspect the entire slide at X10 and higher under the compound microscope.
• Look for spores, fruiting bodies. Identify

Leaf isolation method/Slide

• Collect infected leaf sample from the field.
• Harvest Entyloma vignaespores from infected leaf or pod samples using a needle on to a clean slide.
• Add a drop of lactophenol or cotton blue
• View under microscope to check for spore identification

Treatment/control

• No effective seed treatment against the pathogen
• Seeds for international distribution are grown in certified PFAs
• Active growth field inspection and certification
• Infected plants rogued
• Seeds not harvested from infected field

Procedures in case of positive test at IITA

• Discard. Not for international distribution in compliance with the importing countries’ phytosanitary regulations

For import or export:

• For important germplasm material to be used for crossing, growing on test in the containment, active growth inspection conducted. Plants with smut symptoms are rogued and incinerated
• Seeds from symptomless plants harvested and retested

 

Leaf infection (photo:IITA)

Pod infection (photo:IITA)

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Septoria leaf spot

Scientific name

Septoria vignae Henn.

Other scientific name

Septoria vignicola Vasant Rao

Importance

High

Significance

Not reported.

Symptoms

Leaf symptoms are very pronounced

Spots coalesce to form dark red circular lesions on both leaf surfaces. Lesions also appear on the pods and stems. Pycnidia are formed in the lesions

Septoria vignae (photos:IITA)

Hosts

The only major host recorded is Vigna unguiculata (cowpea).

Geographic distribution

India , East Africa, Savannah zones of tropical Africa, Nigeria

Biology and transmission

Fungus produces conidia in pycnidia. Conidia are septate

Seed borne and seed transmitted

Detection/indexing methods used at IITA

• Collect fresh infected samples from the field.
• Surface sterilized with 5% Na0Cl for 2 mins
• Plate infected leaves/ pods/seeds portions on moist filter paper.
• Incubate at 27^oC for 24hrs to allow the development of the pycnidiospores.
• Pick the developed pycnidia and plate on PDA infused with lactic acid.
• Incubate the plates at 27^oC for 4-6 days.
• Identify under a compound microscope by picking the pycnidia and break it open with a cover slip to identify the spores

Treatment/control

• Seed treatment with mancozeb. 
• Seeds for international distribution are grown in certification schemes
• Active growth field inspection.
• Infected plants rogued

Procedures in case of positive test at IITA

• Discard. Not for international distribution in compliance to the importing countries’ phytosanitary regulations
• For import or export: Seeds are treated with mancozeb and retested after 72 hours for presence /absence of pathogen. Infected lines are rejected.
• For important germplasm material to be used for crossing, growing on test in the containment , active growth inspection, plants with Septoria   symptoms are rogued and incinerated

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Lamptail pod rot of cowpea, Blight of cowpea, Pod rot of cowpea

Scientific name

Choanephora cucurbitarum (Berk. & Ravenel) Thaxt.

Other scientific name

Choanephora americana A. Møller

Importance

High

Significance

The exact data on yield loss are seldom mentionned although in Nigeria. Cowpea losses were estimated at 7-20% by Oladiran (1980).

Symptoms

C. cucurbitarum infects plant tissues that have been damaged either by insects or by physical means. Symptoms vary considerably on different crops

The fungus causes a number of diseases on a range of crops affecting all plant stages: flowering , fruiting , post-harvest, pre-emergence, seedling and vegetative growing and all plant parts; pods, growing points, inflorescence, leaves, seeds, stems and whole plant.

In Nigeria the fungus causes dieback, stem and leaf blight on cowpea.

Visibly field symptoms of Choanephora cucurbitarum on the host tissues have a white hairy appearance resulting from the tall sporangiophores that produce a cluster of brown sporangiola at their tips. On cowpea, symptoms begin as water-soaked lesions at the leaf margins and tips. These lesions became dry and turned olive-green to light brown. Numerous spiny, long sporangiophores developed during dry weather results to total necrosis of the entire plant Turkensteen, 1979; French, 2000.

Symptoms on various plant parts:

Pods: visible mould and whitish spine like mycelium , rot

Growing points: dead heart.

Inflorescence: lesions.

Leaves: lesions; fungal growth; sooty mould; rot; odour.

Seeds: rot.

Stems: external discoloration; canker; dieback; sooty mould.

Whole plant: dieback.

Infected pod (photo:IITA)

Spores (photo:IITA)

Hosts

The major hosts attacked by the fungus are: Vigna unguiculata (cowpea), Abelmoschus esculentus (okra), Amaranthus (grain amaranth), Beta vulgaris var. saccharifera (sugarbeet), Brassica oleracea var. botrytis (cauliflower), Cajanus cajan (pigeon pea), Capsicum (peppers), Capsicum annuum (bell pepper), Capsicum frutescens (chilli), Carica papaya (papaw), Citrullus lanatus (watermelon), Cucumis sativus (cucumber), Cucurbita maxima (giant pumpkin), Glycine max (soyabean), Gossypium (cotton), Ipomoea batatas (sweet potato), Manihot esculenta (cassava), Nasturtium officinale (watercress), Phaseolus vulgaris (common bean), Piper nigrum (black pepper), Pisum sativum (pea), Psidium guajava (guava), Psophocarpus tetragonolobus (winged bean), Ricinus communis (castor bean), Sesamum indicum (sesame), Solanum melongena (aubergine), Solanum tuberosum (potato), Sorghum bicolor (sorghum), Spinacia oleracea (spinach), Vigna mungo (black gram), Vigna radiata (mung bean), and Zea mays (maize).

Geographic distribution

The fungus is worldwide in distribution attacking many crops.

Biology and transmission

C. cucurbitarum produces elongate mycelium without septa. The sporangiola, and typical sporangia are sometimes produced but on separate sporangiophores. The zygospores are formed by fusion of two morphologically similar gametes. Zygospores germinate to produce a sporangium containing sporangiospores French, 2000).

C. cucurbitarum has been reported as a pathogen with 48 species belonging to 37 genera within 17 families. It is a weak parasite that grows on predisposed plants whose tissues have been injured mechanically or damaged by insects during feeding (Cuthbert and Fery, 1975) . Mycelium builds up on the affected plant tissues and enzymes are secreted to overcome the resistance of the healthy tissue, which is then invaded (Agrios, 1978). Makambila and Goma, (1993) reported that Sexual spores on Amaranth debris are the main source of inoculum.The fungus produces thick-walled zygospores which can withstand adverse conditions and germinate when temperatures and moisture conditions are favourable for the production of a sporangium containing sporangiospores. These are then disseminated primarily by air currents (Agrios, 1978).

C. cucurbitarum is seedborne on okra in Malaysia (Tai Luang Huan and Musa Bin Jamil, 1975). The seed borne and seed transmitted nature in cowpea has not been established.

Detection/indexing methods used at IITA

• Blotter method.

Procedure

• Randomly select a sub sample of 500 seeds (or less if fewer seeds are available) from the seed lot.
• Surface disinfection of seeds using 10% Sodium hypochlorite for 3 minutes.
• Rinse the seed in sterile distilled water and blot off excess.
• Plate the material on Blotter and incubate at 28^oC for 4days.Examine plate under stereo microscope.
• Make microscopic slides of fungal fruiting bodies observed in growth.
• Examine under compound microscope to identify the fungal fruiting bodies and spores isolated from the mycelial growth.
• Subculture on NBY to obtain pure cultures of the pathogen for pathogenicity / preservation.Make microscopic slides of the spores and re examine under the compound microscope for confirmation and purity.

Treatment/control

• Seed treatment with mancozeb
• Seeds for international distribution are grown in certified PFAs
• Active growth field inspection and certification
• Infected plants rogued
• Seeds not harvested from infected field

Procedures in case of positive test at IITA

• Discard. Not for international distribution in compliance to the importing countries’ phytosanitary regulations
• For import or export: Seeds are treated with mancozeb and retested after 72 hours for presence /absence of pathogen. Infected lines are rejected.
• For important germplasm material to be used for crossing, growing on test in the containment , active growth inspection, plants with C. cucurbitarum symptoms are rogued and incinerated

References and further reading

Agrios GN. 1978. Plant pathology. London, UK: Academic Press Inc

CAB International. 2007. Crop Protection Compendium, 2007 Edition. Wallingford, UK.

French ER. 2000. Choanephora blight. In Compendium of Potato Diseases. Second edition. St. Paul, Minnesota, USA: APS Press, in press

Makambila C, Goma JB. 1993. Choanephora cucurbitacearum Curr., a new pathogenic fungus of Amaranthus in Congo. Cahiers Agricultures, 2(3):217-219

Oladiran AO. 1980. Choanephora pod rot of cowpea in southern Nigeria. Tropical Pest Management, 26(4):396-402

Tai Luang Huan, Musa Bin Jamil M. 1975. Seed-borne pathogens in okra fruit rot. MARDI Research Bulletin, 3(2):38-45

Turkensteen LJ. 1979. Choanephora blight of potatoes and other crops grown under tropical conditions in Peru. Netherlands Journal of Plant Pathology, 85(2):85-86

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Insects - cowpea

Contributors to this section: IITA, Nigeria (M. Ayodele, L. Kumar).

Contents: Cowpea aphid Bean pod borer, Legume pod borer, Cowpea pod borer Cowpea weevil, Spotted cowpea bruchid, Cowpea seed beetle Leafhoppers Bean fly, French bean miner Flower thrips, Bean flower thrips, African bean thrips

Cowpea aphid

Scientific name

Aphis craccivora

Other scientific names

Aphis medicaginis auct. nec. Koch, 1854
Aphis leguminosae Theobald, 1915
Pergandeida craccivora Koch

Importance

High

Significance

This Aphid is a major economic pest of cowpea. The aphid while feeding removes sap from the leaves, pods, seeds and other aerial plant parts causing damage to the plant resulting in yield reductions.
From experimental data and results, infestation with A. craccivora caused significant reductions in seed yield. (Ofuya, 1989). In a Chinese study A. craccivora infestation, resulted in a reduction in plant height to 41.9% , green leaf area and delayed production of harvestable pods by 30 days (Chang and Thrower, 1981).
Infestations of A. craccivora on cowpeas caused reduction in growth and losses in yield (Annan et al., 1995). Attia et al., (1986). Bishara et al., (1984), reported that A. craccivora was the most damaging pest of cowpeas in Egypt, particularly early in the growing season.
In addition to loss due to damage caused by the aphid, A. craccivora is known to be an important vector of plant viral disease, transmitting over 30 plant viruses, (Wightman and Wightman, 1994).
The aphid also produces honeydew, a substrate which attracts fungi (Mayeux, 1984).

Symptoms

The aphids attacks all growing stages and parts of the plant : flowering, seedling and vegetative growing , points including the leaves and the plant as a whole.

Leaves: distortion, stunting of leaflets, lesions; abnormal colours; premature defoliation; sooty mould

Pod : shrivelling. (Ofuya, 1995; Bottenberg et al., 1998).

Growing points: rosette

Seed : shrivelling

Whole plant : stunting, deformities and yield reductions. (Annan et al., 1997)

Infested cowpea plant (photo:IITA)

Aphids (photo:IITA)

Hosts

The insect feeds on several plants causing damage. Some reported hosts are Vigna unguiculata (cowpea), Arachis hypogaea (groundnut), Cajanus cajan (pigeon pea), Medicago sativa (lucerne), Vigna radiata (mung bean), Capsicum (peppers), Chenopodium quinoa (quinoa), Cicer arietinum (chickpea), Citrus , Gossypium (cotton), Lablab purpureus (hyacinth bean), Lupinus (lupins), Lycopersicon esculentum (tomato), Phaseolus (beans), Phaseolus vulgaris (common bean), Sesamum indicum (sesame), Solanum tuberosum (potato), Theobroma cacao (cocoa), Trifolium (clovers), Vicia faba (broad bean), Vigna catjang , Vigna mungo (black gram).

Geographic distribution

World wide in distribution. It has been reported in Europe, Asia, Africa, Central America, Canada, Mexico, USA, Argentina, Bolivia, Brazil, Chile, Venezuela, Australia, Fiji, New Zealand.

Biology and transmission

Is a shiny black aphid, feeding on the undersurface of the cowpea leaves ,young stems an pods.

Parthenogenetic reproduction occurrs all year round. The aphid is ovoviviparous, The females retain eggs inside their bodies and give birth to small larvae.Young colonies of this small aphids are found on growing points of plants in association with ants. (Soans and Soans, 1971; Patro and Behera, 1991).

Although A. craccivora is polyphagous, it has preference for Leguminosae.

 A. craccivora is dispersed by wind. ( dispersal of the winged forms).

Detection/indexing methods used at IITA

Field inspection during active growth and in storage

Dry seed inspection:

• Spread the seed sample on the seed picking tray. 
• Inspect visually using hand lens to pick out insects, seeds that are discolored, damaged or infested, shrunken, malformed, etc. and record on the scoring sheet.
• Place the cover on the seed picking tray and turn over to inspect the other side of the seeds.
• Based on both observations, give a score of 0-5 for each category: 0=no incidence; 1=1-20% incidence; 2=21-40% incidence; 3=41-60% incidence; 4=61- 80% incidence; and 5=81-100% incidence.
• Identification using the Stereo microscope/ visual

Treatment

Chemical pesticides used for the control of the aphid and ants on the field during active growth:

Chemical control

• Act force 100ml to 20lts water or
• Cyper force 100ml to 20lts water or
• Cyper Diforce 100ml to 20lts water

Protocol

• Spray cowpea with any of the above mentionned insecticide at 7-10 days interval beginning from flower bud initiation.
• In case of severe aphids /ant infestation during seedling stage, one spray may be needed before flowering. Normally four applications of insecticide are adequate to control the insect pests.
• Seed treatment using any available pesticide / seed fumigation using phostoxin

Cultural

• Use insect resistant varieties
• Multiplication plots and environs should be weed and ants free

Procedures in case of positive test at IITA

• Infested lines are incinerated. Not acceptable for international distribution

References and further reading

Annan IB, Schaefers GA, Tingey WM. 1995. Influence of duration of infestation by cowpea aphid (Aphididae) on growth and yield of resistant and susceptible cowpeas. Crop Protection, 14(7):533-538.

Annan IB, Ampong-Nyarko K, Tingey WM, Schaefers GA. 1997. Interactions of fertilizer, cultivar selection, and infestation by cowpea aphid (Aphididae) on growth and yield of cowpeas. International Journal of Pest Management, 43(4):307-312.

Attia AA, El-Heneidy AH, El-Kady EA. 1986. Studies on the aphid, Aphis craccivora, Koch. (Homoptera: Aphididae) in Egypt. Bulletin de la Société Entomologique d'égypte, No. 66:319-324.

Bishara SI, Fam EZ, Attia AA, El-Hariry MA. 1984. Yield losses of faba bean due to aphid attack. FABIS Newsletter, Faba Bean Information Service, ICARDA, No. 10:16-18.

Bottenberg H, Tamò M, Singh BB. 1998. Occurrence of phytophagous insects on wild Vigna sp. and cultivated cowpea: comparing the relative importance of host-plant resistance and millet intercropping. Agriculture, Ecosystems & Environment, 70(2/3):217-229

Mayeux A. 1984. The groundnut aphid. Biology and control. Oléagineux, 39(8/9):425-434; [

Ofuya TI. 1989. The effect of pod growth stages in cowpea on aphid reproduction and damage by the cowpea aphid, Aphis craccivora (Homoptera: Aphididae). Annals of Applied Biology, 115(3):563-566.

Patro B, Behera MK. 1991. Mutualism between the bean aphids (Aphis craccivora Koch) and ants. Orissa Journal of Agricultural Research, 4(3-4):238.

Soans AB, Soans JS. 1971. Proximity of the colonies of the tending ant species as a factor determining the occurrence of aphids. Journal of the Bombay Natural History Society, 68(3):850-851

Wightman JA, Wightman AS. 1994. An insect, agronomic and sociological survey of groundnut fields in southern Africa. Agriculture, Ecosystems & Environment, 51(3):311-331.

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Bean pod borer, Legume pod borer, Cowpea pod borer

Scientific name

Maruca vitrata

Other scientific names

Maruca testulalis Geyer
Crochiphora testulalis Geyer

Importance

High

Significance

Loss in yield not quantified but it is a major cowpea pest in Nigeria .(Odulaja and Oghiakhe 1993).

Symptoms

Maruca  feeds on the tender stems, flower buds, flowers, peduncles, pods, and leaves causing damage to all the plant parts. Symptoms found on:

Flowers: round holes,

Leaves: holes

Pods: distortion

Hosts

The insect attacks 39 hosts of which 37 are leguminous as reported by Rathore and Lal (1998). Arodokoun (1996) listed 23 host plants of M. vitrata in Benin Republic. Some recorded hosts of concern to peasant farmers in the tropics include Vigna unguiculata (cowpea), Cajanus, Cajanus cajan (pigeon pea), Canavalia, Canavalia ensiformis (gotani bean), Fabaceae (leguminous plants), Glycine, Lablab purpureus (hyacinth bean), Phaseolus (beans), Phaseolus lunatus (lima bean), Phaseolus vulgaris (common bean) and Pueraria phaseoloides (tropical kudzu).

Geographic distribution

Belgium, Denmark, France, UK, Asia, China, India, Indoneia, Iran, Japa, Korea, Malaysia, Nepal, Sri Lanka, Thailand, Singapore, Vietnam, Africa, Central America, Mexico, USA, S. America, Australia, Fiji, Papua New Guinea.

Biology and transmission

Adults are not active during the day. They are usually found at rest under the lower leaves of the host plant. They live for an average of 6-10 days, each female laying   up to 200 eggs. Ke et al. (1985) recorded seven generations per year in China.

Detection/indexing methods used at IITA

Field inspection during active growth and inspection during storage

Dry seed inspection

• Spread the seed sample on the seed picking tray. 
• Inspect visually using hand lens to pick out insects, seeds that are discolored, damaged or infested, shrunken, malformed, etc. and record on the scoring sheet.
• Place the cover on the seed picking tray and turn over to inspect the other side of the seeds.
• Based on both observations, give a score of 0-5 for each category: 0=no incidence; 1=1-20% incidence; 2=21-40% incidence; 3=41-60% incidence; 4=61- 80% incidence; and 5=81-100% incidence.
• Identification under the stereomicroscope/ visual

Treatment

• Plant resistant varieties. (IITA has an insect Rearing Unit which rears Maruca sp for research work on Host pest resistance
• Crop rotation
• Biological control, Insect sterility, Use of pheromones/trapping
• Good Agricultural Practice ( Weed free plots)

Chemical control

• Chemical pesticides used for the control of Maruca on the field during active growth:
• Act force 100ml to 20lts water or
• Cyper force 100ml to 20lts water or
• Cyper Diforce 100ml to 20lts water

Procedures in case of positive test at IITA (Discard)

• Infested lines are incinerated. Not acceptable for international distribution

References and further reading

Arodokoun DY. 1996. Importance des plantes-hotes alternatives et des ennemis naturels indigenes dans le controle biologique de Maruca testutalis Geyer (Lepidoptera, Pyralidae), ravageur de Vigna unguiculata Walp. PhD thesis. Quebec, Canada: Universite Laval, 182.

Ke LD, Fang JL, Li ZJ. 1985. Bionomics and control of the legume pod-borer Maruca testulalis Geyer. Acta Entomologica Sinica, 28(1):51-59.

Odulaja A, Oghiakhe S. 1993. A nonlinear model describing yield loss in cowpea (Vigna unguiculata) due to the legume pod borer, Maruca testulalis Geyer (Lepidoptera: Pyralidae). International Journal of Pest Management, 39(1):61-63. 

Rathore YS, Lal SS. 1998. Phylogenetic relationship of host plants of Maruca vitrata.

Indian Journal of Pulses Research, 11(2):152-155.

Singh, S R. 1977. Grain legume Entomology, IITA, Ibadan, Nigeria., 55 pp.

Adult on cowpea (photo:IITA)

Larva stage (photo:IITA)

Pupa stage (photo:IITA)

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Cowpea weevil, Spotted cowpea bruchid, Cowpea seed beetle

Scientific name

Callosobruchus spp.

Other scientific names

Bruchus quadrimaculatus Fabricius 1792
Callosobruchus ornatus (Boheman 1829)

Importance

High

Significance

In Nigeria, yield loss was estimated to 3% of the annual production in 1961/62 . Infestation starts in the pods in the field and are carried over into storage where infestation continues and substantial losses occur (Ojimelukwe et al., 1999). Decrease seed /grain quality.

Symptoms

The insect attacks the fruiting stage, seeds and all stored grains and products.

Pod : eggs cemented to the surface.

Seeds : Round holes.

Hosts

C. maculatus is a major pest of cowpeas, green gram and lentils).
The hosts attacked are Vigna unguiculata (cowpea), Acacia nilotica (gum arabic tree), Cajanus cajan (pigeon pea), Glycine max (soyabean), Phaseolus (beans), stored products (dried stored products), Vigna radiata (mung bean), and Voandzeia subterranea (bambara groundnut).

Geographic distribution

C. maculatus is widely distributed throughout the tropics and sub-tropics. It is found in China, India, Iran, Pakistan, Sri Lanka, Turkey, Africa, Nicaragua, USA, Brazil, Peru, Venezuela, Australia.

Biology and transmission

Adult Callosobruchus maculatus do not feed on stored products. Short lived having a life span of no more than 12 days. Females lay many eggs up to 115 eggs.The beettle lays eggs on maturing cowpea pods.

Detection/indexing methods used at IITA

Field inspection during active growth and inspection of stored seeds for conservation

Dry seed inspection:

• Spread the seed sample on the seed picking tray. 
• Inspect visually using hand lens to pick out insects, seeds that are discolored, damaged or infested, shrunken, malformed, etc. and record on the scoring sheet.
• Place the cover on the seed picking tray and turn over to inspect the other side of the seeds.
• Based on both observations, give a score of 0-5 for each category: 0=no incidence; 1=1-20% incidence; 2=21-40% incidence; 3=41-60% incidence; 4=61- 80% incidence; and 5=81-100% incidence.
• Visual and stereomicroscopic Identification

Treatment/cControl

• Chemical pesticides used for the control in the field and under storage.
• Fumigation of the storage facility
• Seed treatment with phostoxin

Cultural

• Host-Plant Resistance. Resistant varieties are available in IITA
• Harvesting at the right time to prevent infestation of pods in the field
• Cold storage at 4^oC

Procedures in case of positive test at IITA

• Discard. Infested lines are incinerated. Not acceptable for international distribution

References and further reading

Ojimelukwe PC, Onweluzo JC, Okechukwu E. 1999. Effects of infestation on the nutrient content and physicochemical properties of two cowpea (Vigna unguiculata) varieties. Plant Foods for Human Nutrition, 53(4):321-332.

Cowpea weevil, Source Ayodele/Oguntade (IITA)

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Leafhoppers

Scientific name

Empoasca spp.

Other scientific name

Empoasca dolichi

Importance

High

Significance

Not reported.

Symptoms

Emposca attacks cowpea seedlings causing

Leaves :discoloration of veins and margins, cupping

Whole plant : stunting, pre mature drying of the plant.

Empoasca dolichi (photos: IITA)

Hosts

The leaf hoppers attack Vigna unguiculata (cowpea), Arachis hypogaea (groundnut), and Gossypium (cotton).

Geographic distribution

Africa, Nigeria

Biology and transmission

The hopper lays eggs on the underside of the leaves. Adults expentancy life varies from 30-60 days.

Detection/indexing methods used at IITA

Field inspection during active growth

Dry seed inspection

• Spread the seed sample on the seed picking tray. 
• Inspect visually using hand lens to pick out insects, seeds that are discolored, damaged or infested, shrunken, malformed, etc. and record on the scoring sheet.
• Place the cover on the seed picking tray and turn over to inspect the other side of the seeds.
• Based on both observations, give a score of 0-5 for each category: 0=no incidence; 1=1-20% incidence; 2=21-40% incidence; 3=41-60% incidence; 4=61- 80% incidence; and 5=81-100% incidence.
• Visual inspection

Treatment/control

Cultural

• Use resistant varieties
• Planting site sanitation
• Field inspection during active growth
• Removal of infested residues after harvest
• Selection of pest free seeds after threshing for storage
• Seed cold storage at 4^oC
• Good store hygiene

Chemical control, applying sprays during active growth with either:

• act force 100ml to 20lts water or
• cyper force 100ml to 20lts water or
• cyper Diforce 100ml to 20lts water.

Protocol

• Spray cowpea with any of the above mentionned insecticide at 7-10 days interval beginning from flower bud initiation.
• In case of severe infestation during seedling stage, one spray may be needed before flowering. Normally four applications of insecticide are adequate to control the insect pests.

Procedures in case of positive test at IITA

• Discard. Infested lines are incinerated. Not acceptable for international distribution

References and further reading

Singh SR. 1977. Grain Legume Entomology,IITA, Ibadan, Nigeria,., 55pp

Singh SR. 1977. Tropical Grain Legume Bull.9.1-7

Singh RS, van Emden HF. 1998. Ann.Rev. Entom., 24, Rev, 255-278

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Bean fly, French bean miner

Scientific name

Ophiomyia phaseoli

Other scientific names

Melanagromyza phaseoli Vanschuytebroeck, 1951
Agromyza phaseoli Coquillett, 1899
Agromyza destructor Malloch, 1916

Importance

High

Significance

The bean fly is a serious and destructive pest of cow pea and other edible legumes in the tropical and subtropical regions of Asia Talekar (1990.

In Tanzania yield loss which ranges from 30-50% were reported by Wallace, (1939; Walker, (1960). Also, in 1985, the Asian Vegetable Research and Development Center (AVRDC), reported that in Taiwan damage caused by the fly reduced cowpea yield by 32%.

Symptoms

Symptoms caused by the fly are exhibited on various plant parts where they feed and lay eggs,

Leaves : punctures on the upper side, light yellow spots, larval mines turn dark brown, blotchy and drooping, defoliation

Trifoliate leaves : egg holes, silvery, curved stripes of larval mines which are visible on the underside of the leaves , visible tunnels on the upper side of the leaves.

Leaf petiole : swollen

Root : tunnelling , cortex destruction, swollen

Stem : Tunnelling

Whole plant : stunting , Wilting

Hosts

Vigna unguiculata (cowpea) has been reported as a minor host of this fly. Listed major hosts are Fabaceae (leguminous plants), Phaseolus (beans), Phaseolus vulgaris; (common bean), Vigna radiata (mung bean). Minor and wild hosts of the fly have also been reported which include: Cajanus cajan (pigeon pea), Glycine max (soyabean), Phaseolus lunatus (lima bean), Pisum sativum (pea), Psophocarpus tetragonolobus (winged bean), Vigna angularis (adzuki bean), and Vigna mungo (black gram).

Geographic distribution

Bangladesh, China, India, Indonesia, , Iran, Israel, Japan, Jordan, Malaysia, Nepal, Pakistan, Singapore, Saudi Arabia, Sri Lanka, Thailand, Vietnam, Africa, USA, Australia, Fiji, Papua New Guinea

Biology and transmission

The famales of the bean fly are very active on warm clear days seeking young tender leaves for oviposition.  Eggs are laid during the morning hours on the upper side of the leaves, often near the midrib close to the petiole.

Burikam (1980) reported that females lay an average of 77 eggs in cowpea. The adult females live for 23-42 days and males for 31-38 days, and if no food is provided they die in 2-3 days ( Raros (1975) .

Detection/indexing methods used

Field inspection during active growth

Dry seed inspection

• Spread the seed sample on the seed picking tray. 
• Inspect visually using hand lens to pick out insects, seeds that are discolored, damaged or infested, shrunken, malformed, etc. and record on the scoring sheet.
• Place the cover on the seed picking tray and turn over to inspect the other side of the seeds.
• Based on both observations, give a score of 0-5 for each category: 0=no incidence; 1=1-20% incidence; 2=21-40% incidence; 3=41-60% incidence; 4=61- 80% incidence; and 5=81-100% incidence.
• Visual and stereomicroscopic identification

Treatment/control

Cultural

• Use resistant varieties
• Planting site sanitation
• Field inspection during active growth
• Removal infested residues after harvest
• Selection of pest free seeds after threshing for storage
• Seed cold storage at 4^oC

Chemical control

• Seed treatment using carbofuran
• Applying sprays during active growth with either
• Act force 100ml to 20lts water or
• Cyper force 100ml to 20lts water or
• Cyper Diforce 100ml to 20lts water

Protocol

• Spray cowpea with any of the above mentionned insecticide at 7-10 days interval beginning from flower bud initiation.
• In case of severe flies infestation during seedling stage, one spray may be needed before flowering. Normally four applications of insecticide are adequate to control the insect pests.

Procedures in case of positive test at IITA

• Discard. Infested lines are incinerated. Not acceptable for international distribution

References and further reading

AVRDC. 1985. 1983 Progress report. Shanhua, Taiwan: Asian Vegetable Research and Development Center

Burikam I. 1978. Ecological investigation of the bean fly, Ophiomyia phaseoli (Tryon) (Diptera: Agromyzidae) and its natural enemies in Thailand., 71 pp.; [24 fig., unpublished M.Sc. thesis]

Raros ES. 1975. Bionomics of bean fly, Ophiomyia phaseoli (Tryon) (Diptera: Agromyzidae) and its parasites in Hawaii. Ph. D. Thesis. Honolulu, USA: Department of Entomology, University of Hawaii.

Talekar NS. 1990. Agromyzid flies of food legumes in the tropics. New Delhi, India: Wiley Eastern Limited

Walker PT. 1960. Insecticide studies in East African agricultural pests. III. Seed dressing for the control of beanfly, Melanagromyza phaseoli (Coq.) in Tanganyika. Bulletin of Entomological Research, 50:781-793.

Wallace GB. 1939. French bean diseases and bean fly in East Africa. East African Agricultural Journal, 5:170-175.

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Flower Thrips, Bean flower thrips, African bean thrips

Scientific name

Megalurothrips sjostedti Trybom, 1908.

Other scientific names

Taeniothrips sjostedti Trybom
Lundathrips inopinatus Bournier, 1979.

Importance

High

Significance

These Thrips are responsible for the total cowpea yield loss in West Africa

 Serious infestation causing the loss of flower resulting to complete loss of yield was reported by   Childers and Achor, (1995). Alghali (1992) reported that in Nigeria, yield loss of cowpeas was up to 75% when insects attacked during the flower budding and flowering stages.

Symptoms

The Thrips attack the flowering stage infesting the inflorescence and leaves.
Childers and Achor, ( 1995) reported that feeding by M. sjostedti which begins before the flowers open, damages various parts of the cowpea plant especially the flowers. Infestation of the flower and other plant parts results to: 

Inflorescence: distortion and discolouration, abortion, reduced pollen production and flower loss

Leaves: Defoliation

Whole plant : death, yield reduction

Megalurothrips sjostedti(photos:IITA)

Hosts

Legumes are the main hosts of M. Sjostedti and this include Vigna unguiculata (cowpea), Cajanus cajan (pigeon pea), Phaseolus vulgaris (common bean). Tamo et al. (1993b).They also attack some other plants considered as minor hosts such as Arachis hypogaea (groundnut), and some wild hosts.

Geographic distribution

Reported to be found throughout Sub-Saharan Africa, from the high rainfall areas of West to the semi-arid areas of Kenya and Sudan. Meanwhile in Nigeria, it is associated with the dry savanna regions in which cowpeas are produced.

Biology and transmission

Rapid breeding, laying eggs on leaf petioles, peduncles , inflorescences and  pods was reported by Tamo et al., (1993a). Salifu, (1992) reported that development from egg to adult takes about 19 days at 29°C and 58% RH and adults live for about 23 days.

Taylor (1969) reported that the infestation of cowpea plants begin just before flowering. That the adults fligh by day, with the peak of flight activity occurring between noon and 1 pm at a temperature 23-24°C. It had been observed that, both temperature and light intensity influence flight.

Detection/indexing methods used at IITA

Field inspection during active growth.

Dry seed inspection:

• Spread the seed sample on the seed picking tray. 
• Inspect visually using hand lens to pick out insects, seeds that are discolored, damaged or infested, shrunken, malformed, etc. and record on the scoring sheet.
• Place the cover on the seed picking tray and turn over to inspect the other side of the seeds.
• Based on both observations, give a score of 0-5 for each category: 0=no incidence; 1=1-20% incidence; 2=21-40% incidence; 3=41-60% incidence; 4=61- 80% incidence; and 5=81-100% incidence.
• Visual and stereomicroscopic identification

Treatment

Cultural

• Use resistant varieties
• Planting site sanitation
• Field inspection during active growth
• Removal of infested residues after harvest
• Selection of pest free seeds after threshing for storage

Chemical control, applying sprays during active growth with any of the pesticides

• Act force 100ml to 20lts water or
• Cyper force 100ml to 20lts water or
• Cyper Diforce 100ml to 20lts water

Protocol

• Spray cowpea with any of the above mentionned insecticide at 7-10 days interval beginning from flower bud initiation.
• In case of severe Thrips infestation during seedling stage, one spray may be needed before flowering. Normally four applications of insecticide are adequate to control the insect pests.

Biological control

• Research on going on the use of parasitoids and entomopathogens.

Procedures in case of positive test at IITA

• Infested lines are incinerated. Not acceptable for international distribution

References and further reading

Alghali AM. 1992. Insecticide application schedules to reduce grain yield losses caused by insects of cowpea in Nigeria. Insect Science and its Application, 13(5):725-730

Childers CC, Achor DS. 1995. Thrips feeding and oviposition injuries to economic plants, subsequent damage and host responses to infestation. In: Parker BL, et al., eds. Thrips Biology and Management. New York, USA: Plenum Press.

Salifu AB. 1992. Some aspects of the biology of the bean flower thrips Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae) with reference to economic injury levels on cowpea (Vigna unguiculata (L.) Walp). Revue de Zoologie Africaine, 106(5):451-459.

Tamò M, Baumgärtner J, Arodokoun DY. 1993. The spatio-temporal distribution of Megalurothrips sjostedti (Trybom) (Thysanoptera, Thripidae) life stages on cowpea, and development of sampling plans. Mitteilungen der Schweizerischen Entomologischen Gesellschaft, 66(1-2):15-34.

Tamò M, Baumgärtner J, Delucchi V, Herren HR. 1993. Assessment of key factors responsible for the pest status of the bean flower thrips Megalurothrips sjostedti (Thysanoptera: Thripidae) in West Africa. Bulletin of Entomological Research, 83(2):251-258

Taylor TA. 1969. On the population dynamics and flight activity of Taeniothrips sjostedti (Tryb.) (Thysanoptera:Thripidae) on cowpea. Bulletin of the Entomological Society of Nigeria, 1969:60-71.

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Bacteria - cowpea

Contributors to this section: IITA, Nigeria (M. Ayodele, L. Kumar).

Contents: Cowpea bacterial blight, Bacterial blight, Leaf spot Bacterial pustulea Bacterial halo blight, Halo blight (of beans) Bacterial brown spot

Cowpea bacterial blight, Bacterial blight, Leaf spot

Scientific name

Xanthomonas axonopodis pv. vignicola (Burkholder 1944) Vauterin et al. 1995

Other scientific names

Xanthomonas phaseoli f.sp. vignicola (Burkholder) Sabet 1959
Xanthomonas campestris pv. vignicola (Burkholder 1944) Dye 1978

Importance

High

Significance

Although yield losses from the fields have been reported, they have not been quantified

Symptoms

Leaves: pin point water soaked spots on the leaves.

Spots coalesce to form orange lesions surrounded by yellow halo. The bacteria infects also the stems, causing cracking, canker and the pods causing water soaked spots.

Hosts

The major hosts of the bacterial blight pathogen are Vigna unguiculata (cowpea), Crotalaria juncea (sunn hemp), Lablab purpureus (hyacinth bean), Phaseolus vulgaris (common bean), Solanum nigrum (black nightshade), Tephrosia purpurea (purple tephrosia), Vigna mungo (black gram).

Geographic distribution

China, India, Turkey, Botswana, Egypt, Nigeria, S Africa, Sudan, Tanzania, Zimbabwe, Puerto Rico, USA.

Biology and transmission

The bacterium is gram- negative rod, single or in pairs motile by one polar flagellum.Colonies on NBY are yellow and circular. Two biotypes have been isolated and identified morphologically from infected cowpea fields in Nigeria. Isolate 1 which produces yellow colonies on NBYis not sensitive to antibiotic lincomycin while isolate 2 which produces dark yellow/light brown colonies on NBY media is sensitive to lincomycin.

The pathogen is seed borne and seed transmitted. Disease development and spread is favoured by rainfall and the bacterium survives in crop residues.

Detection/indexing methods

Agar method and Serology

Agar test using NBY media, selective media and biochemical analysis:

• Randomly select a subsample of 500 seeds (or less if fewer seeds are available) .
• Surface-sterilise the seeds by placing them in a 10% sodium hypochlorite solution for 3 minutes.
• Rinse the seeds with sterile distilled water, blot dry on sterile paper towel, and place seeds equidistantly on NBY agar media in a 9-cm petri dish.
• Incubate seeds at 25^oC under 12 h fluorescent light or 12 h NUV light for 4 days.
• Inspect each seed carefully under the stereomicroscope. Use a needle or forceps to turn the seed over and to examine the under side.
• Use the compound microscope for the identification of the bacterium
• Pick bacteria colony and streak unto new NBY plates
• Incubate at 28^oC for 48hrs
• On a clean slide, thinly spread bacterial colony; gram stain
• Subculture selected bacteria for further identification on NBY.
• Subject the bacteria to biochemical tests.
• Spot plate the bacterium on MSP and M71 selective media for specie confirmation.

Serology: ELISA using polyclonal antibody for the detection of the bacterium The polyclonal antibody for the detection of X. axonopodis pv vignicola is available in IITA.

Treatment/control

Screen house/ containment facility inspection in collaboration with the National Plant Quarantine service Inspectors for certification and issuance of phytosanitary certificates.

• Seed for export grown in the screen house
•  Inspection during active growth of all the multiplication sites
• Use of resistant varieties
• Seeds for international distribution grown under seed certification schemes and Pest Free areas

Procedures in case of positive test

Discard

For import: Grow seeds under containment. Inspect during active growth.Laboratory testing of vegetative parts (leaves and stem ), seeds using agar method and ELISA

Positive lines discard, not acceptable for international distribution in compliance to National Plant Protection Organization requiring additional declaration of freedom from the X. axonopodis pv vignicola or that X. axonopodis pv vignicola is  not known to occur in the country of origin or multiplication sites.

References and further reading

Elliot C. 1951. Manual of bacterial plant pathogens. 2d ed Chronica Botanica:Waltham, Mass

Moretti C, Mondjana AM, Zazzerini A, Buonaurio R. 2006. Occurence of leaf spot on cowpea (Vigna unguiculata) caused by  Xanthomanas axonopodis pv. vignicola  in Mozambique. [online].

Patel PN, Jindal JK. 1970. Indian Phytopath. Soc. Bull. 6, 28-34.

Watkins GM. 1943. Pl. Reptr. 27, 556

Field symptom (photo: IITA)

yellow and pale yellow colonies (photo: IITA)

Field symptom (photo: IITA)

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Bacterial pustule

Scientific name

Xanthomonas axonopodis pv. vignae

Other scientific names

Not reported.

Importance

High

Significance

Not reported.

Symptoms

It is a foliar disease. The symptoms are visible on the leaves. On the leaves, the symptoms start as small tiny water soaked dots on the underside of the leaves. The dots coalesce to form circular, raised dark water soaked spots on the underside of the leaves and dark brown necrotic spots on the upper side of the leaves’ Older lesions/ pustules become sunkened and dried in the center. 

Leaves turn yellow under severe infection. Defoliation is also a symptom on plants with severe infection. In the field, there is usually some confusion between rust infection (fungal pustules) and bacterial pustules. The first field difference between the two pathogens, is the presence of brown/ pink dust from the leaves of the infected cowpea plants during active growth, this indicates that the pathogen in question is the rust fungi and not a bacterium.

Bacterial pustule (photo:IITA)

Hosts

Cowpea.

Geographic distribution

Widely spread in the humid and savannah eco regions where cowpea is grown in Nigeria. The disease has also been reported in Tanzania and Brazil.

Biology and transmission

The pathogen is seed borne and seed transmitted. Disease spread is favoured by rains

Detection/indexing methods used at IITA

Agar method, Serology and leaf isolation:

Agar test using NBY media, selective media and biochemical analysis:

• Randomly select a subsample of 500 seeds (or less if fewer seeds are available) .
• Surface-sterilise the seeds by placing them in a 10% sodium hypochlorite solution for 3 minutes.
• Rinse the seeds with sterile distilled water, blot dry on sterile paper towel, and place seeds equidistantly on NBY agar media in a 9-cm petri dish.
• Incubate seeds at 25^oC under 12 h fluorescent light or 12 h NUV light for 4 days.
• Inspect each seed carefully under the stereomicroscope. Use a needle or forceps to turn the seed over and to examine the under side.
• Use the compound microscope for closer for the identification of the bacterium
• Pick bacteria colony and streak unto new NBY plates
• Incubate at 28^oC for 48hrs
• On a clean slide, thinly spread bacterial colony; gram stain
• Subculture selected bacteria for further identification on NBY.
• Subject the bacteria to biochemical tests.
• Spot plate the bacterium on MSP and M71 selective media for species confirmation.

Serology:

Conduct ELISA using polyclonal antibodies for the detection of the bacterium.

Treatment/control

• Seed for export grown in the screen house
•  Inspection during active growth
• Use of resistant varieties
• Seeds for international distribution grown under seed certification schemes and Pest Free areas.

Procedures in case of positive test

Discard.

At IITA, for import: Grow seeds under containment. Inspect during active growth. Laboratory testing of vegetative parts (leaves and stem ), seeds using agar method and ELISA.

Positive lines discard, not acceptable for international distribution in compliance to National Plant Protection Organization requiring additional declaration of freedom from X. axonopodis pv vignae or X. axonopodis pv vignae not known to occur in the country of origin or multiplication sites.

References

Patel PN. 1978. 3^rd Int. Congr. Pl. Path, Munich, August, 1978. p 72 ( abstr.).

Williams RJ. 1975. PANS. 21, 253-267.

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Bacterial halo blight, Halo blight (of beans), Grease spot (of beans), Bacterial bean blight

Scientific name

Pseudmonas syringae pv phaseolicola.

Other scientific names

Pseudomonas medicaginis f.sp. phaseolicola (Burkholder) Dowson 1957
Pseudomonas vignae Gardner & Kendrick

Importance

High

Significance

Halo blight is world wide in distribution in the bean growing regions. Walker and Patel, (1964), reported that epidemics have been recorded in some parts of the USA

In some trials with artificial inoculations, losses in seed yield ranging from 2.8-55.4% were obtained (Anon., 1980). Yield losses of 43% in the UK and between 23 and 43% in Michigan were reported by Allen et al. (1998).

Allen et al. (1998) observed crop losses as a result of halo blight in Lesotho, Rwanda and Zimbabwe.

Symptoms

The pathogen infects all the growing stages of the plant: flowering, podding , pre-emergence, and seedling. The pods, growing points, leaves, seeds, stems and whole plant are also infected.  

Symptoms found on the various plant parts are :

Leaves: water-soaked spots that later turn red-brown and necrotic. Lesions; abnormal colours; lime-green halo around the necrotic lesion. Pod: water-soaked, greasy spots that vary in size with brown margins. Seeds: rot, shrivelling and discoloured, some times infected seeds are symptomless. Stem: girdling and rotting of nodes, discoloration; and exudates. Whole plant: seedling blight, chlorosis, dieback, lime green coloration, stunting and distorted (Allen et al., 1998).

Hosts

Cowpea (Vigna unguiculata) is considered to be one of the minor host of the bacterium.

The major hosts infected by the bacterium are: Phaseolus acutifolius (tepary bean), Phaseolus coccineus (runner bean), Phaseolus lunatus (lima bean), Phaseolus vulgaris (common bean).

The minor hosts are: Cajanus cajan (pigeon pea), Centrosema , Desmodium (tick clovers), Glycine max (soyabean), Lablab purpureus (hyacinth bean), Pisum sativum (pea), Pueraria montana var. lobata (kudzu), Vigna angularis (adzuki bean),and Vigna radiata (mung bean).

Geographic distribution

Worldwide

Biology and transmission

Non-sporulating, Gram-negative, aerobic rods. Motile by means of multitrichous polar flagellae. Bacterial colonies are white to cream on agar medium with a bluish colour, producing a green fluorescent pigment on King's medium B agar. Optimum growth temperatures for the bacterium are 20-23°C.

Nine races of the halo blight pathogen isolated from Africa and other bean growing areas, have been characterized based on their reactions to eight differential cultivars. (Taylor et al., 1996). Ariyarathne (1997) identified two new races that occurred in Nebraska, USA.

The pathogen can be stored for up to 5 years at -20°C (Schwartz, 1989).

The disease is seed borne and seed transmitted.

The pathogen survives in infected seed and plant residues on the soil surface. Halo blight is favoured by cool, wet weather (Allen et al., 1996). The bacteria multiply rapidly under favourable environmental conditions with or without the formation of lesions. The water-soaking results from extracellular polysaccharides from bacterial slime interacting with plant tissue (El-Banoby and Rudolph, 1979 After penetration, symptoms develop within 6-10 days at 24-28°C. Halo formation is more common at 16-20°C. Lesions can be without halo at temperatures of 28°C and above (Schwartz, 1989). The bacterium produces a toxin, phaseolotoxin, which contains N-phosphosulfamylornithine. This toxin is responsible for the typical halo symptoms and general chlorosis (Schwartz, 1989).

Detection/indexing methods used at IITA

Agar test using NBY media:

• Randomly select a subsample of 500 seeds (or less if fewer seeds are available).
• Surface-sterilise the seeds by placing them in a 10% sodium hypochlorite solution for 3 minutes.
• Rinse the seeds with sterile distilled water, blot dry on sterile paper towel, and place seeds equidistantly on NBY agar media in a 9-cm petri dish.
• Incubate seeds at 25^oC under 12 h fluorescent light or 12 h NUV light for 4 days.
• Inspect each seed carefully under the stereomicroscope. Use a needle or forceps to turn the seed over and to examine the under side.
• Use the compound microscope for closer for the identification of the bacterium
• Pick bacteria colony and streak unto new NBY plates
• Incubate at 28^oC for 48hrs
• On a clean slide, thinly spread bacterial colony; gram stain
• Subculture selected bacteria for further identification on NBY.
• Subject the bacteria to biochemical tests.
• Spot plate the bacterium on MSP and M71 selective media for specie confirmation.

Treatment/control

• Removal of infected debris after harvest
• Crop rotation using cereals
• Plant disease free, certified healthy seeds and resistant varieties
• Production of seeds under certification scheme and established Pest Free area
• Field inspection during active growth
• Post entry quarantine processing: ELISA , and growing on test under containment to prevent export/ import of infected seeds for research and conservation

Procedures in case of positive test

Discard

For import:

• Post entry quarantine processing by growing the lines under containment facility to intercept the bacteria.
• Inspection during active growth in company of the Plant quarantine inspectors
• Rogue lines with symptoms and incinerate
• ELISA testing for all symptomless lines
• Discard positive lines by incineration

For export:

• Seeds harvested from the multiplication fields are seed health tested
• Using the agar method and selective media previously described in addition to ELISA test. Infect lines are discarded by incineration.
• Not acceptable for international distribution

References and further reading

Allen DJ, Buruchara RA, Smithson JB. 1998. Diseases of common bean. In: Allen DJ, Lenne J, editors. The Pathology of Food and Pasture Legumes. Wallingford, UK: CAB International, 214.

Anon. 1980. Germplasm screening for desirable variability. Disease loss studies. Centro Internacional de Agricultura Tropical: 1979 Bean program. Annual Report.1980, 19-22.

Ariyarathne HM. 1997. Pathogenic variation for the halo blight bacterium and mapping of loci for multiple diseases in common bean. PhD diss. University of Nebraska, Lincoln

El-Banoby FE, Rudolph K. 1979. A polysaccharide from liquid cultures of Pseudomonas phaseolicola which specifically induces water-soaking in bean leaves (Phaseolus vulgaris L.). Phytopathologische Zeitschrift, 95(1):38-50;

Schwartz HF. 1989. Halo blight. In: Schwartz HF, Pastor-Coralles MA, editors. Bean Production problems in the Tropics. Cali, Colombia: Centro Internacional de Agricultura Tropical (CIAT).

Taylor JD, Teverson DM, Allen DJ, Pastor Corrales MA. 1996. Identification and origin of races of Pseudomonas syringae pv. phaseolicola from Africa and other bean growing areas. Plant Pathology

Walker JC, Patel PN. 1964. Splash dispersal and wind as factors in epidemiology of halo blight of bean. Phytopathology, 54:140-141.

Field Symptom (photo: IITA)

Growth on MSP (photo: IITA)

Control plate of MSP (photo: IITA)

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Bacterial brown spot

Scientific name

Pseudmonas syringae pv syringae

Other scientific names

Phytomonas syringae (van Hall) Bergey et al. 1930
Pseudomonas vignae var. leguminophila (Burkholder) Magrou & Prévot 1948

Importance

High

Significance

P. syringae pv. syringae is seedborne on several crops throughout the world. It attacks several economic crops causing great losses. The bacterium was reported to have caused epidemics on Phaseolus vulgaris cvBonusplantingsin the Transvaal highveld in South Africa where crop losses of up to 55% were reported. The pathogen was also detected in commercial seed stocks (Serfontein, 1994).

Symptoms

• P. syringae pv. syringae attacks the flowering, podding , post-harvest, seedling and vegetative growing stages of the plant. It also affects the leaves, stems, inflorescence, pods, seeds, roots, and the whole plant

• Some infected plants are symptomless

• The bacterium causes frost injury to plants, at relatively high freezing temperatures

• Symptoms found on the various plant parts are:

•  Leaves : small, water-soaked spots first appearing on the lower sides of the leaves, the spots enlarge, coalesce, form necrotic lesions, blacken and die

• Stem: water-soaked, sunken brown lesions, splitting at the surface, girdling,

• Pods: small water-soaked spots , enlarge, coalesce, turn brownish or reddish colored with age (Agrios, 1988; Hall, 1991).

• Seeds: discoloration, spots, and

• Seedling: dieback.

Field symptom (photo:IITA)

Hosts

The pathogen has several hosts comprising of mono and dicots.

The major hosts of Ps syringae pv syringae are : Vigna unguiculata , (cowpea)Vitis , (grape)Vitis vinifera , (grapevine)Zea mays (maize)Abelmoschus esculentus , (okra)Allium cepa , (onion)Allium porrum , , (leek)Citrus aurantium , (sour orange)Citrus limon , (lemon)Citrus maxima , (pummelo)Citrus medica , (citron)Citrus reticulata , (mandarin)Citrus sinensis , (navel orange)Citrus x paradisi , (grapefruit)Coffea arabica , (arabica coffee)Cucumis sativus , (cucumber)Cucurbita , (pumpkin)Cucurbita maxima , (giant pumpkin)Cyphomandra betacea , (tree tomato)Juglans regia , (walnut)Lablab purpureus , (hyacinth bean)Lactuca sativa , (lettuce)Lycopersicon esculentum , , (tomato)Malus domestica , (apple)Mangifera indica , (mango)Medicago sativa , (lucerne)Musa x paradisiaca , (plantain)Nicotiana tabacum , (tobacco)Oryza sativa , (rice)Panicum , (millets)Panicum miliaceum , (millet)Passiflora edulis , (passionfruit)Pennisetum glaucum , (pearl millet)Pennisetum purpureum , (elephant grass)Persea americana , (avocado)Phaseolus coccineus , (runner bean)Phaseolus lunatus , (lima bean)Phaseolus vulgaris , (common bean)Piper nigrum , (black pepper)Pisum sativum , (pea)Prunus amygdalus , Prunus armeniaca , (apricot)Prunus avium , (sweet cherry)Prunus domestica , (plum)Rosa , (roses)Sorghum bicolor , (sorghum)Sorghum halepense , (Johnson grass)Sorghum sudanense , (Sudan grass)Triticum aestivum , (wheat)Vicia faba , (broad bean)Vicia villosa , Vigna angularis (adzuki bean)

 The only recorded minor host is Chenopodium quinoa (quinoa)

Geographic distribution

Worldwide.

Biology and transmission

P. syringae pv. syringae is an aerobic, unicellular Gram-negative rod, motile having one to several polar flagella. The bacterial colonies are circular, milky-white, raised, glistening, translucent, smooth surface, and entire margin. It produces a green fluorescent pigment on King's B medium. The bacteriium produces two lipopeptide toxins, syringomycin and syringopeptin. (Hutchison and Gross, 1997.

This species is represented by strains which are heterogeneous genetically (Gardan et al., 1997). P. syringae pv. syringae comprise of more than 50 distinct pathogens identified as pathovars (Dye et al., 1980; Young et al., 1996). P. syringae pv. syringae is a pathovar originally isolated from lilac but now found infecting several hosts. The pathogen survives on a number of crops and non-crop species, which serve as sources of primary inoculum for infection ( Hall, 1991a, b.). The bacterium is found in the soil, water and on plant surfaces. The bacterium is seed borne and seed transmitted. Spreads through plant parts, rain and wind.
On cowpea, P. syringae pv. syringae, survives in infected seeds and stems. From the seed, it infects the cotyledons, spread to the leaves or enter the vascular system and cause systemic infection resulting in stem and leaf lesions. Disease spread and intensity is favored by rains.

Detection/indexing methods at IITA

Agar method NBY, followed by:

• Selective medium
• and Semi-selective medium
• Serology ( ELISA)

Treatment/control

Seed treatment using mancozeb has not been effective.

• Use of disease-free seeds
• Plant resistant varieties. These are available in IITA
• Crop rotation, discard of plant debris after harvest
• Seed multiplication for international distribution in Pest Free Areas.

Procedures in case of positive test

For import:

• Post entry quarantine processing by growing the lines under containment facility to intercept the bacteria.
• Inspection during active growth in company of the plant quarantine inspectors
• Rogue lines with symptoms and incinerate
• ELISA testing for all symptomless lines
• Discard positive lines by incineration

For export:

• Seeds harvested from the multiplication fields are seed health tested
• Using the agar method and selective media previously described in addition to ELISA test. Infected lines are discarded by incineration.
• Not acceptable for international distribution

References and further reading

Agrios GN. 1988. Plant pathology. London, UK: Academic Press Inc. (London) Ltd.

CAB International. 2007. Crop Protection Compendium, 2007 Edition. Wallingford, UK: CAB International

Goszczynska T, Serfontein JJ. 1998. Milk-Tween agar, a semiselective medium for isolation and differentiation of Pseudomonas syringae pv. syringae, Pseudomonas syringae pv. phaseolicola and Xanthomonas axonopodis pv. phaseoli. Journal of Microbiological Methods, 32(1):65-72.

Hall R. 1991. Compendium of Bean Diseases. St Paul, Minnesota, USA: APS Press.

Higley PM, McGee DC, Burris JS. 1993. Development of methodology for non-destructive assay of bacteria, fungi and viruses in seeds of large-seeded field crops. Seed Science and Technology, 21(2):399-409

Hutchison ML, Gross DC. 1997. Lipopeptide phytotoxins produced by Pseudomonas syringae pv. syringae: comparison of the biosurfactant and ion channel-forming activities of syringopeptin and syringomycin. Molecular Plant-Microbe Interactions, 10(3):347-354

Mohan SK, Schaad NW. 1987. An improved agar plating assay for detecting Pseudomonas syringae pv. syringae and P. s. pv. phaseolicola in contaminated bean seed. Phytopathology, 77(10):1390-1395

Serfontein JJ. 1994. Occurrence of bacterial brown spot of dry beans in the Transvaal province of South Africa. Plant Pathology, 43(3):597-599.

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