Nematodes - common bean
Contributors to this page: CIAT, Colombia (Maritza Cuervo, Cesar Medina, Jose Luis Ramirez, Socorro Balcazar, Josefina Martinez, Daniel Debouck).
Root-knot nematode disease; Lesion nematode disease
Scientific name
Meloidogyne spp. and Pratylenchus spp.
Significance
Nematode infestations at high initial population densities cause significant yield losses. For example, yield losses may reach 10% to 80% with lesion nematodes, and 50% to 90% with root-knot nematodes. In addition, plant-parasitic nematodes, particularly the root-knot nematodes, are known to predispose many crop plants to various soil-borne microorganisms that induce root rot and wilt diseases.
Symptoms
Plants infected with nematodes do not necessarily exhibit characterisitic foliar symptoms. Severely infected plants may show chlorosis, stunting, necrosis of leaf margins and wilting during periods of moisture stress. Root-knot nematode infestation includes wilting, loss of vigour, 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 are obligate, endoparasites with a wide host range, including agronomic crops and weeds that belong to many plant families. Numerous plant parasitic nematodes are associates with roots and soils of bean and other plants throughout the world. As a genus, they are reported as parasites of over 3000 host plants and individual species often have a wide host range. Jensen et al. (1977) listed some 874 crop species as hosts of the seven or eight species commonly occurring in the western U.S. Root-knot nematodes may feed on the roots of grasses and certain legumes without causing galling.
Geographic distribution
Southeast Asia, South America and USA.
Biology and transmission
Root-knot nematodes (Meloidogyne spp and Pratylenchus spp) survive in soil as eggs and larvae. Length of survival in soil varies with the nematode species, stage of development, soil texture, soil moisture and soil aeration. Dissemination of nematodes among fields and growing regions can occur via irrigation water, vegetative plant parts and soil infested with eggs or larvae which adhere to farm tools, animals, or man. Depending upon the host and temperature, the entire life cycle may be completed in 17-57 days.
Detection/indexing method at CIAT
- Washing sedimentation test, visualization in stereomicroscopy and microscopy.
Treatment/control
To control root-knot nematodes, resistant plant varieties and chemicals are used. 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. Growing crops antagonistic to nematodes such as Tagetes minuta L. (marigolds), Crotalaria spectabilis or Indigofera hirsute L. can reduce populations or even cause the elimination of root-knot nematodes. As with other cultural control methods, nematode populations will rapidly increase as soon as susceptible crops are grown. Crop rotation can reduce population levels of root-knot nematodes when beans are planted once every two or three years in rotation with non-hosts such as maize. Other cultural practices which reduce nematode populations include long fallow periods, deep plowing, weed control and, where practical, flooding for one or two weeks. However, the effectiveness of these organisms in the field and their economic commercial use are not encouraging. Chemical control of plant parasitic nematodes with nematicides is very effective and used widely on annual agronomic crops. However, use of nematicides is expensive for a crop like beans and requires care in handling, and often the use of special equipment for application.
References and further reading
Abawi GS, Crosier DC. 1985. Control of lesion nematodes on snap beans with fenamiphos. 1984. Fungi, Nemat. Test (USA) 40:94.
Frison EA, Bos L, Hamilton RI, Mathur SB, Taylor JD, editors. 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.
Schwartz HF, Pastor-Corrales MA, editors. Bean production problems in the tropics. Centro Internacional de Agricultura Tropical (CIAT). Cali, Colombia.
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