P.19. Necrosis disease threat to pulse crop cultivation and its management
Abstract
A sudden outbreak of virus disease was noticed in pulse crops viz., cowpea, blackgram, greengram and soybean during 2003 and 2004 in Tamil Nadu state. The affected plants showed necrosis symptoms on veins, midrib, petiole, stem and bud. In blackgram and greengram in addition to the above symptoms, yellowing, cupping and rolling of leaves were noticed. Plants affected at early growth stage were severely stunted with reduced internodal length and proliferation of axillary shoots. High population of thrips was noticed on these crops, and also on groundnut grown adjacently. Thrips found on these crops were of two types, Scirtothrips dorsalis and Thrips palmi. The cowpea recorded 92% necrosis incidence with 20 S. dorsalis per leaf and 30 Thrips palmi per flower. Soybean recorded 40% necrosis incidence with 15 S. dorsalis per leaf and 5 T. palmi per flower, blackgram and greengram recorded 25% disease incidence with 10 S. dorsalis per leaf and 10 T. palmi per flower. Based on symptoms and high presence of thrips in the fields, involvement of Peanut bud necrosis virus (PBNV) in the disease etiology was suspected. To test this, sap extracted from the infected plants were inoculated to the indicator host, Nicotiana tabacum, which expressed chlorotic spots confirming the virus presence. However, accurate confirmation is necessary by testing with PBNV antibodies. The fungicide Imidacloprid as seed treatment (3 ml per kg of seed) along with foliar spray (1 ml L−1) gave good control over the disease.
