Bacteria - pearl millet
Contributors to this page: ICRISAT, Patancheru, India (RP Thakur, AG Girish, VP Rao).
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Brown Spot; Bacterial brown spot
Scientific name
Pseudomonas syringae pv. syringae van Hall.
Other scientific names
Pseudomonas syringae pv japonica
Importance
High
Significance
The diseases caused by this bacterium are very important throughout the world. For instance, bacterial brown spot occurs wherever beans are grown, and canker diseases of fruit trees caused by P. syringae pv. syringae are widespread and may be devastating, causing economical losses.
Symptoms
The symptoms first appear on the lower sides of the leaves as small, water-soaked spots. The spots enlarge, coalesce, and form larger areas that later become necrotic. The bacteria also enter the vascular tissues of the leaf and spread into the stem. The infected area, which is surrounded by a narrow zone of bright, lemon yellow tissue, turns brown, becomes rapidly necrotic, and through coalescence of several small spots, may produce large dead areas of various shapes. The disease produces identical symptoms on the stems, pods and seeds. In addition, light-cream or silver bacterial exudates are often produced on the lesions under moist conditions.
Hosts
Multilateral hosts like gramineae and leguminosae.
Geographic distribution
Worldwide
Biology and transmission
P. syringae pv. syringae is a rod shaped, gram-negative with polar flagella. P. syringae tests negative for arginine dihydrolase and oxidase activity, and forms the polymer levan on sucrose nutrient agar. It is known to secrete the lipodepsinonapeptide plant toxin syringomycin, and it owes its yellow fluorescent appearance when cultured in vitro on King's B medium to production of the siderophore pyoverdin . Pathogen is seed borne and it will spread through the infected seed from season to season (Gaudet and Kokko 1986; Venette et al. 1987). Diseases by P. syringae are favoured by wet, cool conditions - optimum temperature for disease development is around 12 - 25°C, although this can vary according to the pathovar involved. The pathogen is seedborne, and is dispersed between plants via rain splash (Hirano and Upper 1990).
Detection/indexing methods at ICRISAT
- Pre export field inspection and agar plate method.
Treatment/control
- No suitable seed treatment to eradicate infection.
Procedures followed in CGIAR in case of positive test at ICRISAT
- So far not detected at ICRISAT.
References and further reading
Gaudet DA, Kokko EG. 1986. Seedling disease of sorghum grown in southern Alberta caused by seedborne Pseudomonas syringae pv. syringae. Canadian Journal of Plant Pathology 8: 208-217.
Hirano SS, Upper CD. 1990. Population biology and epidemiology of Pseudomonas syringae Annual Reviews in Phytopathology 28:155-177
Venette JR, Lampa RS, Albaugh DA, Nayes JB. 1987. Presumptive procedure (dome test) for detection of seed borne bacterial pathogens in dry beans. Plant Disease 71: 984-990.
Scientific name
Xanthomonas vasicola pv. holcicola (Elliott).
Other scientific names
Bacterium holcicola, Phytomonas holcicola, Pseudomonas holcicola, Xanthomonas campestris pv. holcicola, Xanthomonas holcicola.
Importance
High
Significance
The disease is important only occasionally during springtime under warm weather conditions and becomes less serious during hot and dry summer months.
Symptoms
First symptoms are narrow, water-soaked, transparent leaf streaks, 2-3 mm wide ´ 2-15 mm long, appearing as early as the second leaf stage of the seedling. Lesions soon turn red, become opaque, and at intervals may broaden into somewhat irregularly shaped oval spots with tan centers and narrow red margins. In severe cases, these coalesce to form long irregular streaks and blotches extending across all or much of the leaf blade, with dead tissue bordered by narrow, dark margins between the reddish-brown streaks. Abundant bacterial exudates are produced as light-yellow droplets, which dry to thin white or cream scales (Williams et al. 1978).
Hosts
Panicum miliaceum (broomcorn millet), Setaria italica (foxtail millet), Sorghum halepense (aleppo grass), Sorghum sudanense (Sudan grass), Sorghum bicolor (common sorghum) and Zea mays (maize).
Geographic distribution
Xanthomonas vasicola pv. holcicola is prevalent worldwide (Elliott 1930).
Biology and transmission
Xanthomonas vasicola pv. holcicola is bothsoilborne and seedborne, and is also transmitted by infected plant debris.
Detection/indexing methods at ICRISAT
- Pre export field inspection
Treatment/control
- No seed treatment.
Procedures followed in case of positive test at ICRISAT
- So far not detected.
References and further reading
Elliott C. 1930. Bacterial streak disease of sorghum. Journal of Agricultural Research 40: 963-976.
Williams RJ, Frederiksen RA and Girard JC. 1978. Sorghum and Pearl Millet Disease Identification Handbook. Information Bulletin No. 2. ICRISAT, Patancheru 502324, AP, India. 88pp
Scientific name
Xanthomonas campestris (Pammel) Dowson
Other scientific names
Xanthomonas rubrisorghi, Xanthomonas pennisiti, Xanthomonas annamalaiensis.
Importance
High
Significance
Bacterial leaf streak is of minor importance.
Symptoms
Initial symptoms include narrow, water-soaked, transparent leaf streaks, 2-3 mm wide by 2-15 mm long generally appear from the second leaf stage of the seedlings. Lesions soon turn red, become opaque, and at intervals may broaden into somewhat irregularly shaped oval spots with tan centers and narrow red margins. In severe form, these coalesce to form long irregular streaks extending across the leaf blade. Abundant bacterial exudates are produced as light-yellow droplets, which dry to thin white or cream scales (Williams et al. 1978).
Hosts
Panicum miliaceum (broomcorn millet), Setaria italica (foxtail millet), Sorghum halepense (aleppo grass), Sorghum sudanense (Sudan grass), Sorghum bicolor (common sorghum) and Zea mays (Qhobela and Claflin 1988).
Geographic distribution
It is reported from Nigeria and Senegal.
Biology and transmission
Bacterial colonies are yellow and mucoid on the nutrient agar medium. Bacterial cells are aerobic, motile, gram-negative, rod-shaped which differ pathologically, serologically, and by membrane protein patterns from other pathovars of X. campestris. Cells measure 0.45 ´ 2.25 mm and have one polar flagellum. Optimal growth occurs between 26 and 30 oC (Rangaswami et al. 1961).
Detection/indexing methods at ICRISAT
- Pre export field inspection and agar plate method are used.
Treatment/control
- No seed treatment is available.
Procedures followed in case of positive test at ICRISAT
- So far not detected.
References and further reading
Qhobela M, Claflin LE. 1988. Characterization of Xanthomonas campestris pv. pennamericanum pv. nov., causal agent of bacterial leaf streak of pearl millet. International Journal of Systematic Bacteriology 38: 362-366.
Rangaswami G, Prasad NN, Eswaran KSS. 1961. Two new bacterial diseases of sorghum. Andhra Agricultural Journal 8: 269-272.
Williams RJ, Frederiksen RA, Girard JC. 1978. Sorghum and Pearl Millet Disease Identification Handbook. Information Bulletin No. 2. ICRISAT, Patancheru 502324, AP, India. 88pp.
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