Crop Genebank Knowledge Base

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Nematodes - forage legume

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); ICARDA, Syria (Siham Asaad).

Stem and bulb nematode infection
Root-knot nematode infestation

Stem and bulb nematode infection

Scientific name

Ditylenchus dipsaci (Kühn) Filipjev


A major pest in temperate climates and high-altitude regions of the tropics and subtropics.


Plants become distorted and stunted; infected tissues are spongy; damage can predispose plants to other problems.

Field shows irregular areas of sparse growth.

Clover and alfalfa show reduction of internode length and swollen stems.


More than 400 host plants have been described for D. dipsaci. The species is subdivided in races. The Allium race also attacks oats, sugar beet, Swiss chard, spinach and legumes (fababean, bean, pea, soybean).

Medicago sativa, Glycine max, Trifolium spp.

Geographic distribution

Cosmopolitan, except tropical lowlands; temperate regions where it is one of the most devastating plant parasites; USA.

Biology and transmission

The nematode is carred inside the seed, and it is a seed and soil borne nematode.

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.

Predisposes alfalfa to Phytophthora megasperma.

Detection/indexing method

  • At CIAT: No significant importance
  • At ICARDA:, Nematode extraction

References and further references

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.

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Root-knot nematode infestation

Scientific Name

Meloidogyne spp.


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.


Root knot nematodes have a broad host range of more than 200 reported plants.

As a genus, they are reported as parasites of over 3000 host plants, and individual species often have a wide host range. Some 874 crop species act as hosts of the 7 or 8 species commonly occurring in the western U.S.

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 centre of the root. Root-knot gall tissue is firm without a hollow centre, 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) 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: Visualization in Stereomicroscopy and Microscopy

Procedure followed at the center in case of positive test

  • Species rotation in regeneration fields.

References and further reading

Frison EA, Bos L, Hamilton RI, Mathur SB, Taylor JD. (eds). 1990. FAO/IBPGR Technical Guidelines for the Safe Movement of Legume Germplasm. Food and Agriculture Organization of the United Nations, Rome/International Board for Plant Genetic Resources, Rome.

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