Evaluation of Bacillus sp. strains for biological control of gummy stem blight, Didymella bryoniae (Auersw.) in watermelon (Citrullus lanatus)

Abstract

The gummy stem blight caused by Didymella bryoniae (Auersw.) is a major and destructive disease of watermelon in Vietnam. Bacillus species have been used to control plant diseases as biological control agents. This study was carried out at the Department of Crop Production and Plant Protection, Phu Yen province, Vietnam during 2020 – 2021 to determine fungal inhibition of D. bryoniae DB-03 in in vitro and disease suppression of gummy stem blight under greenhouse conditions by Bacillus sp. strains namely S1A1, S1F3, S13E3, S18F11, and S20D12, which were isolated from stem-base of groundnut in central Vietnam. Results revealed that, all the tested strains of Bacillus sp. showed good inhibitory effect on the hyphal growth of D. bryoniae strain DB-03 in potato dextrose broth. Among the strains, Bacillus sp. S20F12 had highest inhibition of the mycelia growth of D. bryoniae strain DB-03 with an antagonistic efficiency of 60.7% at 10 days after fungal inoculation. Bacillus sp. reduced gummy stem blight under greenhouse conditions. At 21 days after fungal inoculation, disease incidences were low in the plants treated with Bacillus sp. S18F11 and S20D12 by 60.0% and 63.3%, respectively. The results would contribute to the knowledge of antagonistic activities of the Bacillus to optimize the biological control programme against D. bryoniae.