Morphological and Cultural Variability among Bipolaris sorokiniana Isolates Causing Spot Blotch of Wheat

Abstract

Spot blotch, caused by Bipolaris sorokiniana (Sacc.) Shoemaker, is one of the most destructive foliar diseases of wheat and results in significant yield losses under warm and humid conditions. The present investigation was conducted to examine the cultural and morphological variability among eight isolates of B. sorokiniana collected from different wheat-growing regions of Uttarakhand, India. The isolates were cultured on Potato Dextrose Agar (PDA) medium and evaluated for colony morphology, radial mycelial growth, conidial pigmentation, septation, shape, and dimensions. Considerable variability was observed among the isolates for all the characteristics evaluated. Colony colour varied from white, whitish grey, and light grey to dark grey and greyish black, whereas colony texture ranged from cottony and fluffy to appressed and suppressed growth. After eight days of incubation, radial mycelial growth ranged from 40 to 80 mm, with isolate BS-1 (Pantnagar) exhibiting the maximum growth and BS-6 (Gadarpur) exhibiting the minimum. Microscopic observations revealed variation in conidial pigmentation from light brown and olive brown to dark brown. Conidial septation ranged from 2 to 8 septa, whereas conidial shapes were elliptical, oblong, or slightly curved. Conidial length and width ranged from 58.06 to 85.53 μm and from 16.08 to 23.31 μm, respectively. Despite these differences, all isolates exhibited morphological characteristics consistent with those of B. sorokiniana. The observed phenotypic diversity indicates substantial variability within the pathogen population, which may influence disease development, pathogenic behaviour, and management strategies. These findings provide valuable baseline information for accurate pathogen identification and support future studies on pathogenic variability, resistance breeding, and the integrated management of wheat spot blotch.