Pathogenicity of Berkeleyomyces basicola and Berkeleyomyces rouxiae on cotton (Gossypium hirsutum) in Australia

Abstract Black root rot of cotton ( Gossypium hirsutum ) caused by Berkeleyomyces rouxiae is a major seedling disease in New South Wales, Australia. Berkeleyomyces rouxiae is morphologically identical to B. basicola and both are present in Australian agricultural systems. However, only B. rouxiae has been recovered from diseased-cotton to date. In this study, we for the first time evaluate pathogenicity of carrot- B. basicola and cotton- B. rouxiae directly on two cotton varieties (cv. Sicot 714B3F and Sicot 746B3F) and carrot ( Daucus carota ) seedlings (cv. Topweight), and marketed carrot roots. Both Berkeleyomyces species enabled to infect and induce black root rot symptoms on cotton at two inoculum levels i.e. 10 3 and 10 4 spores/mL potting mix. However, the disease severity based on the necrotic percentage were significantly lower ( p = 0.0001) in seedlings inoculated with 10 3 B. basicola spores/mL than that with B. rouxiae . In co-inoculated assays, co-infection was detected directly on seedlings of both varieties detected with species-specific PCR assays. In this study, Sicot 714B3F appeared more resilient than Sicot 746B3F although both varieties were severely infected with cotton- B. rouxiae isolate (disease severity > 90%). On carrot, both species failed to incite black rot symptoms on seedlings. However, carrot- B. basicola incited more necroses on marketed carrot roots than cotton- B. rouxiae . This study provides better understanding of B. basicola and B. rouxiae pathogenicity on cotton which can affect their prevalence in the field. Therefore, we propose to adapt alternative surveillance strategies to monitor black root rot pathogen of cotton and further explore the host range of the two Berkeleyomyces species that would provide valuable information for disease management.