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Among the diseases
affecting lentil, the ones caused by fungi are the most important.
These diseases affect different parts of the lentil plant and are
caused by diverse groups of fungi. Some affect mainly the roots
and stems; others affect foliage and pods. The fungal diseases of
lentil are described here under two groups: root and stem diseases,
and foliar diseases. Among the former are fusarium wilt, collar
rot, wet root rot, dry root rot, stem rot and damping-off. Of these,
fusarium wilt is the most widespread and important disease.
Among the foliar diseases are ascochyta blight, rust, gray mold, anthracnose, downy mildew, powdery mildew, alternaria leaf spot and several other leaf spots. Of these, ascochyta blight and rust are the two economically important lentil diseases.
Fusarium wilt
The disease is widespread in almost every country where lentil is grown. It has been reported from Argentina, Canada, Chile, Colombia, Czechoslovakia, Egypt, Ethiopia, France, Hungary, India, Jordan, Morocco, Nepal, Poland, Sudan, Syria, Turkey, Tunisia, Uruguay, the USA and the former USSR. The disease can cause complete failure of the crop, especially in a warm spring and dry and hot summer.
The disease is caused by Fusarium oxysporum Esp. lentis Vasudeva and Srinivasan, which is essentially a soil-borne fungus. Its host range is limited to lentil. It produces three types of spores: oval or kidney-shaped microconidia; thin-walled, multicellular (4-6 cells) macroconidia with a definite foot cell and a pointed apical cell, and chlamydospores formed singly in macroconidia, or terminal or intercalary in the hyphae. Optimum temperature for fungal growth is around 25°C.
External contamination of seeds by the fungus is usual, and high levels of the fungus may be carried in plant debris. Severity of the disease also depends on the inoculum potential in soil. Sowing date affects wilt incidence because it determines what proportion of the growth cycle of the crop is at optimum or near-optimum temperature for fungal growth
Symptoms: The disease appears in the field in patches at both seedling and adult stages (Fig. 1). Seedling wilt is characterized by sudden drooping followed by drying of leaves and the whole seedling (Fig. 2), and apparently healthy looking roots with reduced proliferation.
The adult wilt symptoms first appear at flowering to late pod-filling stage (Fig. 3) and are characterized by sudden drooping of top leaflets of the affected plant (Fig. 3), leaflet closure without premature shedding (Fig. 4), dull green foliage color followed by wilting of the whole plant or individual branches (Fig. 4), apparently healthy looking root system with a slight reduction in the lateral roots which are as difficult to pull out as the healthy plant, and no internal discoloration of the vascular system in most cases.
Seeds from plants affected in mid- to late podfilling stage are often shrivelled.
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