Root-knot nematodes are plant-parasitic nematodes from the genus Meloidogyne. They exist in soil in areas with hot climates or short winters. About 2000 plants are susceptible to infection by root-knot nematodes and they cause approximately 5% of global crop loss (Sasser and Carter, 1985). Root-knot nematode larvae infect plant roots, causing the development of root-knot galls that drain the plant’s photosynthate and nutrients. Infection of young plants may be lethal, while infection of mature plants causes decreased yield.
Symptoms: These are among the most spread plant parasitic nematodes and cause heavy losses, particularly to vegetable, even more than all other diseases combined together. The plant growth is reduced, unthrifty growth and tendency of plant to wilt during warm days. In case of high populations, young seedlings may be killed over large areas without any trace of gall formation. If the suspected plant is carefully lifted up with a showel. The plant roots will show galls on them. The galls can be split open and white pearly, typically elongate pyriform females can easily be seen under a microscope. Crop damage in warm and long season parts of the world is generally much more conspicuous than the cooler and short season areas. Nematode injury is usually associated with plant parasitic fungi, which find their way into the weakened roots. In 1955, Sasser showed that tobacco plants inoculated with Black Shank of Tobacco (Phytophthora parasitica var. nicotianae) fungus caused mortality 0-30% while other inoculated with nematode and fungus showed 75-100% mortality after 3 weeks of planting.
Casual Agents :
- Meloidogyne javanica
- M. arenaria
- M. incognita
- M. hapla etc
Life Cycle:Elongate ovate eggs are laid in a gelatinous egg sac. On an average female lays 200-500 eggs. This nematode passes through 5 stages. 1st and 2nd stage develop within the egg. 2nd stage larvae come out. They are slender, worm like and move in soil in search of the host. The larvae may find their way in the mother gall or somewhere else. In a single gall, all the stages of the nematode may be found. Larvae prefer root tips for penetration. They are unable to penetrate into large roots. Females remain near the cortex while larvae penetrate to near about the central cylinder.
After the establishment of larvae giant cells develop Female larvae become obese spindle shaped. 3rd and 4th stage cuticles are also produced without any moult. The larvae at this time are flask shaped. When gonads develop, final moult takes place and 2nd, 3rd, and 4th stage cuticles are shed simultaneously. After 3rd stage, male remains active, slender, with small spear, and bluntly tail without bursa. Reproduction can take place without males and a single larva may produce as many as seven generation.
Control:
- Crop rotation: Not successful to a great extent. In case of cotton and peanut nematodes, a three years rotation of alfalfa has proved useful. Anyhow rotation of alfalfa, tobacco, corn, and cereals will produce satisfactory yield.
- Fallowing of land: Dry fallowing with 2-3 deep ploughing during hotter summer months in long season areas, is an excellent measure. winter vegetable should be short season.
- Soil fumigation: DD mixture @ 7 lbs/10,000 sq.ft. EDB+DD mixture @ 8 lbs/10,000 sq.ft. VAPAN @ 3 lbs/100 sq. ft. Nemagon (DBCP) 10 gl/acre; etc.
- Root residues should be collected and removed or allow them to decay before the application is made, other wise, a large number of population will escape during fumigation.
