Morphological and molecular diversity of rice blast isolates from Terai foothills of the Himalayas

Rice blast disease, caused by Magnaporthe oryzae (formerly as Pyricularia grisea), is a major threat to rice production globally, causing devastating yield losses up to 30-50% of rice production annually. Here, we analysed 48 isolates collected from rice fields in the Terai foothills of the Himalayas, India, to assess pathogen occurrence in a new agroecological zone, potentially influenced by climate change and favourable environmental conditions. All isolates were screened for virulence and pathogenicity, and two highly virulent isolates (UBKV1 and UBKV2) were selected for detailed characterization of their morphological, growth, and genetic variability. Significant differences (p-value=4.16 x 10-) were observed in conidial dimensions, with UBKV2 producing larger spores (33.61 {micro}m) compared to UBKV1 (28.07 {micro}m). In terms of growth, mycelial biomass (fresh weight) and sporulation intensity was also higher in UBKV2 (22.98 g and 2315.5) than UBKV1 (15.82 g, and 1812.3) when they grew under the same conditions. Distinct colony growth patterns were observed on different media, particularly on Mathurs medium and Rice Straw Extract Dextrose Oatmeal Agar, where UBKV2 exhibited suppressed growth and unique pigmentation. Phylogenetic analysis of the ITS region revealed sequence similarities ranging from 95.11% to 100% among the isolates. UBKV2 showed closer genetic relatedness to isolates from Odisha (96.95-97.23%) than to UBKV1 (95.57%), highlighting significant genetic differentiation. These findings demonstrate substantial morphological, cultural, and genetic variation within M. oryzae populations in the Terai foothills, providing important insights into pathogen evolution, virulence mechanisms, and implications for region-specific resistance breeding strategies.