Abstract:

Collar rot disease incited by Sclerotium rolfsii is one of the most destructive soil borne disease of soybean that causes 30-40% yield losses in India. The disease has also been found to occur frequently in the soybean field of North Eastern Hill states and major losses incurred because of pre and post-emergence seedling mortality, wilting and weakening of older plants. The Present investigation was focused on screening resistant genotypes, assessment of yield losses and in-vitro efficacy of plant extracts, bio-control agents (BCAs) and chemical fungicides against S. rolfsii. The study revealed that the pathogen produced white fluffy mycelium and large numbers of dark brown coloured spherical sclerotia of size 0.3-5 mm in diameter on infected plants. Twenty soybean genotypes were screened against collar rot. Genotypes NRC-80, MACS-1188, RKS-52, and AMS-l were found resistant, whereas other nine and seven genotypes were categorized as moderately resistant and moderately susceptible respectively. The genotype NRC-80 showed the least (0%) per cent disease index (PDI) and minimum yield loss (1.02%), whereas the genotype MACS-I059 showed the highest PDI (46.15%) and maximum yield loss (46.17%). Seven plant extracts tested for their comparative efficacy by poisoned food technique on inhibition of radial growth and sclerotial germination of S. rolfsii. Study revealed that garlic extract was more effective followed by neem extract in reducing the radial growth of the fungus, whereas sclerotial germination was inhibited only by garlic extract (18.34%). Dual culture assays carried out to test five antagonists revealed that Trichoderma viride was more effective than T. harzianum in reducing radial growth of the fungus, but one of the Trichoderma spp. was found effective in inhibiting sclerotial germination. Among three bacterial antagonists evaluated, Pseudomonas putida was highly effective in reducing the radial growth as well as sclerotial germination of S. rolfsii. Simultaneously, seven fungicides viz. Benofit, Bavistin, Contaf, Folicur, Jatayu, Antracol and Bilzeb were also evaluated in-vitro for inhibition of radial growth and sclerotial germination of S. rolfsii. Folicur was highly effective in inhibition of radial growth and sclerotial germination followed by Benofit and Contaf. The best performed plant extracts, BCAs and fungicides may be recommended as important component of integrated disease management, which needs further in-vivo investigations against collar rot of soybean under mid hill conditions of Meghalaya.