Nematodes - forage grass
Contributors to this page are: CIAT, Colombia (Maritza Cuervo, Cesar Medina, Jose Luis Ramirez, Socorro Balcazar, Josefina Martinez, Daniel Debouck); ILRI, Ethiopia (Jean Hanson, Janice Proud, Juvy Cantrell).
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Stem and bulb nematode infection
Scientific name
Ditylenchus dipsaci (Kühn) Filipjev
Significance
A major pest in temperate climates and high-altitude regions of the tropics and subtropics.
Symptoms
Plants become distorted and stunted; infected tissues are spongy; damage can predispose plants to other problems
Field shows irregular areas of sparse growth
Hosts
More than 400 host plants have been described for D. dipsaci. The species is subdivided in races.
Oat race: polyphagous on cereals, most grains, rye, corn, and oats.
Geographic distribution
Cosmopolitan, except tropical lowlands; temperate regions where it is one of the most devastating plant parasites; USA
Biology and transmission
Nematode is a migratory endoparasite. At the beginning of the crop season, 4th-stage juvenile enters young tissues, especially seedlings when below the soil surface. Feeding breaks down middle lamellae; nematode probably secretes a pectinase enzyme; plant parts become ‘crisp’ and are easily broken. Migration on plant parts above ground requires free water, and may occur after rain or sprinkler irrigation. Nematode enters through stomata or by direct penetration.
Cardinal temperatures for nematode activity and infection are 10oC - 22oC -30oC. In soil, they survive as fourth stage larvae at temperatures not exceeding 35oC.
Infestation occurs readily in heavier soils and during times of high rainfall or in sprinkler-irrigated areas.
Nematode is spread around field by equipment, irrigation; spreads readily in tail water.
Detection/indexing method
- at CIAT: Washing roots and microscopic identification
- at ILRI: Waching roots and microscopic identification
Treatment/control
- Systemic insecticides and hot water treatment
Procedure followed at the centers in case of positive test:
- Reject accession and new regeneration started in clean field area.
References and further reading
Diekmann M. 1997. FAO/IBPGR Technical guidelines for the safe movement of Germplasm. No. 18. Allium spp. Food and Agriculture Organization of the United Nations, Rome/International Plant Genetic Resources Institute, Rome.
Root-knot nematode infestation
Scientific name
Meloidogyne spp.
Significance
Quarantine importance for vegetative cuttings due to limited distribution and severe damage caused on plant quality and quantity.
Symptoms
Root knot nematode infestation includes wilting, loss of vigor, yellowing and other symptoms similar to a lack of water or nutrients. Plants often wilt during the hottest part of the day, even with adequate soil moisture, and leaves may turn yellow. Fewer and smaller leaves and fruits are produced, and plants heavily infested early in the season may die.
Root knot nematodes usually cause distinctive swellings, called galls, on the roots of affected plants. Infestations of these nematodes are fairly easy to recognize by digging up a few plants with symptoms, washing or gently tapping the soil from the roots, examining the roots for galls. The nematodes feed and develop within the galls, which may grow to as large as 1 inch in diameter on some plants but are usually much smaller. The water- and nutrient-conducting abilities of the roots are damaged by the formation of the galls. Galls may crack or split open, especially on the roots of vegetable plants, allowing the entry of soil-borne, disease-causing microorganisms.
Root knot nematode galls are true swellings and cannot be rubbed off the roots, as can the beneficial nitrogen-fixing nodules on the roots of legumes.
Hosts
Root knot nematodes have a broad host range of more than 200 reported plants.
Geographic distribution
Southeast Asia, South America, USA
Biology and transmission
The root-knot nematodes (Meloidogyne spp.) form easily recognized galls on the roots. Galls result from growth of plant tissues around juvenile nematodes which feed near the center of the root. Root-knot gall tissue is firm without a hollow center, and is an integral part of the root; removing a root-knot gall from a root tears root tissue.
They are difficult to control and can be spread easily from garden to garden in soil (for example, on tools, boots, etc.) and plant parts.
Certain marigolds (Tagetes sp.) suppress root knot nematodes. The effect of marigolds is greatest when they are grown as a solid planting for an entire season. When grown along with annual vegetables or under trees or vines (intercropping), nematode control is usually not very good. As with other cultural control methods, nematode populations will rapidly increase as soon as susceptible crops are grown.
Root knot nematodes may feed on the roots of grasses and certain legumes without causing galling.
Damage is most serious in warm, irrigated, sandy soils.
Detection/indexing method
- at CIAT: Washing roots and microscopic identification
- at ILRI: Not applicable
Treatment/control
- Certain marigolds (Tagetes sp.) suppress root knot nematodes. The effect of marigolds is greatest when they are grown as a solid planting for an entire season. When grown along with annual vegetables or under trees or vines (intercropping), nematode control is usually not very good. As with other cultural control methods, nematode populations will rapidly increase as soon as susceptible crops are grown.
- Systemic insecticides and hot water treatment.
Procedure followed at the centers in case of positive test
- Reject accession and new regeneration started in clean field area.
References and further reading
http://plantclinic.cornell.edu/FactSheets/nematodes
http://www.ipm.ucdavis.edu/PMG/PESTNOTES
Diekmann M, Putter CAJ. (eds.) 1995. FAO/IPGRI Technical Guidelines for the Safe Movement of Germplasm. No. 14. Small Grain Temperate Cereals. Food and Agriculture Organization of the United Nations, Rome/International Plant Genetic Resources Institute, Rome.
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