(II). Reniform nematode (Rotylenchulus reniformis)
- It is a sedentary semi-endoparasite, ranks next to Meloidogyne as far as damage to vegetables is concerned.
- This nematode is a limiting factor in vegetable production in tropical and subtropical areas.
- The nematode has a very wide host range and attacks over 100 plant species including many vegetable crops like tomato, brinjal, okra, cucumber, potato, cowpea, ginger, onion, sweet potato, beans etc.
Biology
- Immature females are infective, penetrate the root cortex, assume kidney shape and become sedentary.
- Males are not parasitic and remain vermiform.
- Egg to egg life cycle is completed on okra in 24–29 days.
- The first moult takes place in the egg itself. The nematode can develop up to immature stage in water through a series of three superimposed moults without feeding.
- The reniform nematode can survive in moist soil in the absence of hosts for 7 months and for 6 months in dry soil.
Symptoms
- Non specific above-ground symptoms include unthrifty plant growth, stunting, yellowing and leaf curling.
- Root necrosis in cortical region has been observed following infection.
- Females and their adhering egg masses can be easily observed under the dissecting microscope.
- Soil adhering to the gelatinous egg masses often gives them a dark appearance, aiding in detection.
Management
- Cultural: Nematode densities have been found to reduce in rotations with maize, sugarcane finger millet, groundnut, capsicum, chillies, sugarcane and other grasses. Soil amendments such as animal manure and cotton seed cakes play a supportive role in control of reniform nematode.
- Physical: Short periods of flooding also reduce nematode population in the field. The nematode can also be eradicated from infested soil following treatment with 50o C hot water for 5 min. Soil solarization may provide season-long control of R. reniformis on tomato even under conditions of abundant rainfall and extended cloud coverBiological: Very little has been done regarding biocontrol of this nematode, although it would be a good target for antagonists. Paecilomyces lilacinus are known to reduce nematode densities in field. Endomycorrhizal fungus Glomus fasciculatum reduces the penetration and reproduction of R. reniformis on tomato and cucumber. Crop rotation to increase mycorrhizae might be important in regulating population densities.
- Chemicals: A wide range of fumigant and non-fumigant nematicides is effective in controlling R. reniformis. The combination of nematicides and neem cake increased the yield of tomato and reduced nematode densities in field trials. Single foliar application of oxamyl reduced the nematode penetration. All granular nematicides reduce R. reniformis densities in tomato.
- Integrated: Soil solarization or soil mulching with clear plastic for 5 weeks combined with carbofuran @ 3kg a.i. /hectare or solarization with neem cake results in to a significant increase in tomato or cucumber yields and reduction in nematode densities.
(III) Root lesion nematode (Pratylenchus spp.)
It is a migratory endoparasitic nematode, ten species of which have been found in the rhizosphere or roots of vegetable crops. But only P. indicus has been found to be most prevalent under Indian conditions.
It infests vegetables like tomato and brinjal.
Biology
- This nematode reproduces sexually and has a simple life cycle.
- Eggs are deposited preferably in root but may be deposited in soil also.
- The first moult occurs inside the egg and J2s emerge out and moult thrice before becoming adults.
- All the juvenile stages and adults are infective and capable of penetrating the root tissue.
- Egg to egg life cycle is completed in 30 to 90 days depending upon the species, host plant and environmental conditions.
Symptoms
- Stunted, chlorotic plants lacking vigour, poor fruiting and die back are the main aerial symptoms.
- Root symptoms are in the form of necrotic lesions which may coalesce with one another as the infection spreads and may girdle the root. These lesions are the ideal sites for infection by other microorganisms leading to disease complexes.
Control
Lesion nematodes can be controlled with fumigant and non-fumigant nematicides. Integrated management practices as in root-knot and reniform nematodes would control this nematode.
(IV) Tylenchorhynchus brassicae (Stunt/stylet nematode)
- Out of twenty-two species of Tylenchorhynchus found in the rhizosphere of vegetable crops, only Tylenchorhynchus brassicae which infects cabbage, cauliflower, knol-khol, lettuce, radish and tomato, holds economic significance in India.
- Though most of the tylenchorynchus species are migratory ecto-parasitic nematodes feeding on epidermal cells of the roots, T. brassicae has been observed to penetrate through out the cortex.
- The nematode causes poor germination and stubby root condition leading to stunting of cabbage and cauliflower.
Crop rotation with non host crops and inter-culturing with margosa has been reported to improve the growth of susceptible vegetable crops.
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