<div>Background: The gummy stem blight caused by the fungal pathogen Didymella bryoniae (Auersw.) is a common and serious disease of watermelon plants in Vietnam. Bacillus species have been used to control plant diseases as biological control agents. The objectives of this studies were to determine the fungal inhibition of D. bryoniae and disease suppression of gummy stem blight under greenhouse by Bacillus sp. strains. 
 
Methods: The study was carried out at University of Agriculture and Forestry, Hue University during 2022-2023. Six potential Bacillus strains namely S1A1, S1F3, S13E2, S13E3, S18F11 and S20D12 isolated from stem-base of groundnut in central Vietnam were tested its fungal inhibition of D. bryoniae and disease suppression of gummy stem blight. 
 
Result: All tested strains of Bacillus sp. showed inhibition of the hyphal growth of D. bryoniae strain DB-01 in potato dextrose broth. Among the strains, Bacillus sp. S20F12 had highest inhibition of the growth of mycelia of D. bryoniae strain DB-01 with an antagonistic efficiency of 65.7% at 10 days after fungal inoculation. By 21 days after fungal inoculation, disease incidences were low in the plants treated with Bacillus sp. S20D12 and S1F3 by 46.6 and 50.0% and disease severity by 15,3% and 20.6%, respectively. As results, watermelon plants were prevented from damage of gummy stem blight caused by D. bryoniae strain BD-01 by Bacillus sp. S20D12 and S1F13. The results would contribute to the knowledge of antagonistic activities of the Bacillus to optimize the biological control against D. bryoniae.</div>

Biological Control of Gummy Stem Blight Caused by Didymella bryoniae (Auersw.) on Watermelon by Bacillus sp. Strains