A simple carrot agar medium for isolation of black root rot pathogen of cotton seedlings

Black root rot (BRR) is a major seedling disease in cotton in Australia. BRR is caused by a soilborne fungus Thielaviopsis basicola , recently re-described as Berkelyomyces spp., that was reported for the first time in 1990 in northern New South Wales (NSW), Australia. The disease is now prevalent across NSW. Since the first detection, much research has been focused exclusively on management; however, little has been investigated to understand the BRR pathogen population. Isolation and collection of pure fungal cultures are essential for investigation of the pathogen diversity and pathogenicity. However, isolation of T. basicola is recalcitrant. In this study, T. basicola were successfully recovered from BRR diseased cotton seedlings in the past three seasons by using a simple 5% carrot agar amended with 100 ppm streptomycin. T. basicola was recovered within three days with the percentage of recovery ranging from 55–76% during the first isolation attempt. This carrot medium provided a simple and vigorous means for isolation of T. basicola .