Paramyrothecium roridum has recently emerged as a notable foliar pathogen of cotton in India, yet information on its population diversity remains limited. This study provides the first integrated assessment of the morpho-genetic diversity of P. roridum across traditional and non-traditional cotton-growing regions of Haryana. Thirty isolates collected from diseased cotton leaves exhibited clear phenotypic variability in colony appearance, sporodochial structures, growth patterns, and conidial dimensions, indicating considerable morphological plasticity within the species. ITS rRNA sequencing grouped all isolates into a single major clade with a small internal subgroup, reflecting overall genetic coherence with minor evolutionary divergence. Analysis of 544 nucleotide sites identified 20 segregating sites, demonstrating measurable polymorphism among isolates. Non-traditional cotton regions displayed greater genetic variability and more segregating sites than traditional areas, suggesting a broader genetic base and the influence of distinct ecological or agronomic selection pressures. Despite this variability, the low genetic differentiation coefficient indicated that all isolates constitute a largely panmictic population with unrestricted gene flow across cotton-growing zones. By combining morphological and molecular characterization, this study enhances understanding of P. roridum diversity, its dispersal potential, and evolutionary dynamics within Haryana. To the best of our knowledge, this is the first detailed investigation of P. roridum population structure in Haryana's cotton ecosystem.
Saini et al. (Thu,) studied this question.