Survey, isolation and characterisation of Bipolaris sorokiniana (Shoem.) causing spot blotch disease in wheat under the climatic conditions of the Indo–Gangetic plains of India

Wheat spot blotch has emerged as a disease of significant concern in recent years. The pathogen <i>Bipolaris sorokiniana</i> can infect stems, leaves, roots and seeds, increasing its impact. The pathogen is particularly prevalent in the wheat growing zone of West Bengal, which provides congenial conditions for the growth and development of the pathogen. However, its knowledge under West Bengal conditions is inadequate. To address this issue, isolates of <i>Bipolaris sorokiniana</i> were collected from different locations in West Bengal. The pathogenic species were identified via comprehensive morphological studies supplemented with internal transcribed spacer (ITS)-rDNA sequence analysis and pathogenicity. The disease severity of the twelve isolates collected varied among the surveyed locations, ranging from 44.03% to 81.48 %. The greatest radial growth was observed in BSC11 (50.07 mm), whereas the lowest growth was recorded in BSC9 (6.47 mm) at 96 h after inoculation. Molecular studies confirmed that the isolates were <i>Bipolaris sorokiniana</i>. In pathogenicity assays, BSC11 presented the highest area under the disease progress curve (AUDPC) (380.05) and percent disease index (PDI) among the isolates at 20 dai (38.33 %). The correlation matrix revealed that disease severity was positively correlated with the number of spores (r² = 0.70), growth rate of mycelia (r² = 0.77), and lesion size (r² = 0.74), whereas the length of the spores, incubation period, and latent period were negatively and significantly correlated with disease severity. Establishing the aggressiveness of a pathogen is pivotal in studying host‒ interactions. Our study established BSC11 as a highly virulent pathogen isolate that can be used further for comprehensive analysis of <i>wheat‒Bipolaris sorokiniana</i> interactions.