Studies on Alternaria macrospora causing boll rot in Bt-cotton

A study was conducted at the Department of Plant Pathology, College of Agriculture, VNMKV, Parbhani during 2024-25. Alternaria macrospora causing boll rot in cotton is one of the most devastating and perplexing cotton disease, experiments were carried out to isolate the pathogen, identify it based on cultural and morphological characteristics, as well as microscopic observations, and demonstrate its pathogenicity on cotton plant and cotton boll by detached boll method. Furthermore, various culture medias, including Potato dextrose agar, Richards Agar, Czapek’s Dox agar, V8 juice agar, Conn’s agar, Corn meal and Sabouraud’s dextrose agar medium, were tested to determine which media is best for growing the pathogen Alternaria macrospora. Alternaria macrospora radial mycelial growth was investigated in vitro across all culture mediums. All of the media tested promoted the growth of the test pathogen. The results showed that, of the seven culture medias examined, potato dextrose agar was the most suited and promoted the most radial mycelial development (90.00 mm). The second-best was corn meal (51.78 mm), followed by Czapek’s Dox agar (47.17 mm) for radial mycelial growth.