Morpho-molecular and pathogenic variability of Pyricularia isolates in millets and rice

Blast disease caused by Pyricularia species is a significant constraint in millets and rice worldwide. The present research attempted at studying the occurrence, isolation and identification of blast pathogen, with attention on the systematic position in the Pyricularia spp. complex and host-related pathotypes. To differentiate between genera and assess host specificity, internal transcribed spacer (ITS) related phylogenetic analysis has been used. During the 2024–2025 cropping seasons, a field assessment was carried out in Tamil Nadu millet and rice-growing districts as well as in a few locations in Andhra Pradesh. Leaf samples exhibiting typical blast symptoms was collected. Fifty blast isolates isolated by standard tissue isolation on potato dextrose agar (PDA) were purified using the single-spore isolation method. Morphological analysis showed a significant variance between the isolates with radial mycelial growth ranging from 62–89 mm with plate cover in 10–16 days. The typical pyriform, 3 celled conidia of Pyricularia spp. are produced by abundant sporulation in colony which vary in colour from grey to olivaceous. Detached-leaf inoculation revealed typical spindle-shaped lesions within 3–6 days after inoculation (DAI). Pearl millet isolates were most virulent (0.14–1.38 cm²; MgPM1 highest), followed by barnyard millet (0.04–0.48 cm²; MgBM3), while finger millet (0.06–0.21 cm²; MgFM4) and foxtail millet (0.02–0.18 cm²; MgFoxM3) showed lower virulence. The ITS-based molecular identification yielded ~560 bp amplicons, with 92–100 % similarity to Pyricularia spp. In the National Centre for Biotechnology Information (NCBI) GenBank, confirming identity. However, ITS lacked resolution for species and pathotype differentiation, requiring further phylogenetic and pathogenicity analysis.