Unraveling Diversity in Alternaria brassicae Affecting Indian mustard: Morphological, Pathogenic and Molecular Approaches.

Abstract

Alternaria blight, caused by Alternaria brassicae (Berk.) Sacc. stands as one of the most prevalent and damaging disease afflicting mustard (Brassica juncea) cultivation on a global scale. In the current investigation, Alternaria infected leaf samples were collected from twenty-one distinct locations across eleven states of India. Isolates were comprehensively analyzed for genetic diversity through morphological variability, pathogenicity and molecular phylogeny studies. The results showed significant variation in cultural characteristics and radial growth among A. brassicae isolates, with growth ranging from 59.80 mm in Ab17 to 88.58 mm in Ab19. Pathogenicity data revealed that there were 5 highly virulent, 13 moderately virulent, and 3 least virulent isolates which was confirmed in digital image analysis of diseased spots on leaves using MATLAB's Image Processing Toolbox. This suggests the evolutionary potential of A. brassicae and its ability to adapt to different geographical regions. Based on sequencing of amplified ITS region and β-tubulin gene, all the isolates showed 100 per cent homology to the sequences of A. brassicae strain J3 (GenBank CM016504.1). Furthermore, DNA fingerprinting pattern generated by ISSR markers, all the isolates were individually grouped into 3 main clusters. Comparative analysis established congruence between DNA finger prints, virulence pattern, location and morphological grouping of A. brassicae isolates. The present research holds significance in precisely categorizing the pathogen responsible for crop infection, enabling us to develop a targeted and efficient strategy for future disease control measures.