Journal of Advances in Biology & Biotechnology

Sunflower is an important edible oilseed crop primarily cultivated for its vegetable oil production and is also grown as an ornamental crop. Among the major diseases affecting sunflower, Alternaria blight is one of the most destructive diseases limiting sunflower productivity, causing severe yield loss under warm and humid conditions. The disease can cause yield losses ranging from 11% to 77%. Studying cultural and morphological variation in the pathogen plays an important role in accurately identifying the causal organism. Therefore, twenty-four isolates of Alternaria infecting sunflower were obtained from different districts of Karnataka during Kharif 2024-25 to study cultural and morphological variation and to identify of Alternaria species infecting sunflower in Karnataka. Colony pigmentation varied among dark grey, grey, brown, white with a brown centre, and cream-coloured colonies. Conidial length and width ranged from 18.54 µm to 64.92 µm and from 7.51 µm to 15.30 µm, respectively. Based on cultural and morphological characters, 20 isolates were identified as Alternaria alternata and 4 isolates as Alternariaster helianthi. PCR amplification of the isolates using ITS primers (ITS1 and ITS4) produced an amplicon of ~550 bp. Sequencing and BLAST analysis of representative isolates confirmed the identity of five isolates as A. alternata and one isolate as Alternariaster helianthi. Phylogenetic analysis further resolved the isolates into two distinct clades with strong bootstrap support, corroborating the morphological identification. The present study demonstrates the coexistence of A. alternata and Alternariaster helianthi in sunflower-growing regions of Karnataka. Integrating cultural, morphological and molecular methods provides useful information for pathogen identification and the development of effective disease management programmes.