Incidence of white mould of bean and characterization of its causal pathogen, Sclerotinia sclerotiorum in Kashmir valley, India

Abstract White mould caused by Sclerotinia sclerotiorum affects the quality and quantity of bean crop. The aims of this study were to evaluate the incidence and severity of white mould disease in four districts of Kashmir valley and to characterize the morphological variability of 60 Sclerotinia sclerotiorum isolates from bean plants. Three bean fields per village and five villages per district were chosen randomly for sampling. The highest incidence among surveyed areas was found in Ganderbal (37.94%) and lowest in Shupiyan (19.98%). The disease severity was highest in district Ganderbal (15.54%) and lowest in district Shupiyan (7.94%). Single spore method was used to isolate the fungus. Sixty isolates of the causal organism were isolated from bean plants collected from the surveyed areas and pathogenecity test was carried out following Koch’s postulates. Morphological characters of the different isolates, like number of sclerotia per Petri plate, time required for formation of the first sclerotium and average weight and shape of the sclerotia were studied. Among sixty isolates of S. sclerotiorum isolated from bean, it was observed that 25% of the isolates had abundant mycelium, 25% had irregular mycelium, half of the isolates had thin mycelium. 75% of the isolates had white colour and 25% had beige coloration. 25% of the isolates had a round shape, and 75% had a diverse shape. Sclerotia were detected in 50% of the cases in a regular pattern along the colony edge, 25% spread throughout the colony, and 25% in concentric circles. The mean number of sclerotia per colony ranged from 11.68 (SS55) to 32.32 (SS26). The mean number of days for formation of the first sclerotium ranged from 9.3 (SS30) to 17.7 (SS60). The average weight of sclerotia ranged from 0.0918 (SS58) to 0.2475 (SS21). The variation in disease incidence across different sites and the morphological variation of the isolates can be due to differences in genetic constitution as well as environmental conditions.