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Collar rot
The disease occurs in almost every region where lentils are cultivated, and is especially prevalent in areas with high soil moisture in the seedling stage of the crop. The disease, in general, is minor and economically unimportant except in some parts of North India where the crop, which is grown after a rice crop, suffers in the seedling stage.
The disease is caused by Sclerotium rolfsii Sacc. The perfect stage of the fungus, although not reported on lentil, is Corticium rolfsii Curzi. The causal fungus is soil-borne and can survive in soil as sclerotia for a long time even under adverse weather conditions. It is favored by excessive soil moisture and high temperatures (above 25-30°C).
Symptoms: The affected seedlings, generally found in small patches in the field, lie flat on the ground. They may have yellowing of lower leaves, depending upon the stage at which the seedling became infected.
The characteristic symptoms are seen near the collar region, which is rotted and discolored. This weakens the seedling and causes its collapse. In cases of the prolonged survival of seedling due to later infection, the affected plants show general yellowing, drooping of leaves and death of plants.
On the affected collar region, white strands of the fungus mycelia are characteristic (Fig. 5). Rapeseedlike brown sclerotia also are seen on the affected collar region. Diseased seedlings/plants are easily pulled out.
Control: Seed treatment with thiram + PCNB (1:1) at 0.25% offers acceptable control of the seedling mortality caused by the disease.
The use of resistant varieties provides good control of this soil-borne disease. Several resistant lines have been identified.
Adjusting the date of sowing to avoid high soil moisture and high temperatures will help the crop escape the disease.
Wet root rot
The disease, like collar rot, occurs in almost all lentil-growing regions of the world, but is a minor disease and economically unimportant in most regions except in some parts of India and Ethiopia.
The disease is caused by Rhizoctonia solani Kuhn, which is soil borne. The fungus has a perfect stage in Thanatephorus cucumeris, the role of which has not yet been established. The disease is favored by high soil moisture and temperatures.
Symptoms: Symptoms are observed at both seedling and adult plant stages depending upon the time of infection, but in both cases, the affected plants show yellowing of leaves progressing from lower to upper plant part (Fig. 6).
The roots of the affected plants become reddish brown and the diagnostic symptom is a clear constriction at the collar portion or below it (Fig. 6). In the early stages of infection the main root below the constriction remains healthy and intact but may become affected as the infection progresses (Fig. 7). In such cases the seedlings are easily pulled out.
In cases of infection occurring in the late seedling stage, the plants are able to survive for some time showing yellowing of leaves but ultimately succumbing to root infection. The affected roots are 'wet' in appearance and hence the name of the disease.
Control: Seed treatment with PCNB (0.3%) provides satisfactory disease control, especially of seedling mortality.
Use resistant/tolerant varieties
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