Occurrence, Identification and Preliminary Biological Control of Bulb Rot of Onion (Allium cepa)

Onion bulb rot was observed in low-temperature warehouses in Mae Wang District, Chiang Mai, Thailand in 2022. The pathogens were isolated and identifi ed as Pantoea agglomerans and Burkholderia gladioli based on morphological and biochemical characterization, pathogenicity tests, and 16S rRNA gene sequences. Biological control is regarded as a safer and more sustainable strategy than chemical control and has elicited great attention for disease control. Bacillus sp. isolate BB22 was isolated from rhizosphere soil and was evaluated for its preliminary potential to inhibit the growth of onion bulb rot bacterial pathogens by the dual culture technique. The results showed inhibition zones of P. agglomerans of 30.1 mm and B. gladioli of 13.0 mm. Molecular identifi cation of Bacillus sp. isolate BB22 was performed by using 16S rRNA and gyrA gene sequences and confi rmed as Bacillus velezensis. PCR amplifi cation of the bmyB, fenD, ituA, and srfAA genes coding for bacillomycin, fengycin D, iturin A, and surfactin, respectively, showed the potential for the production of these antibiotics. This study revealed the potential application of B. velezensis as a biocontrol agent against bulb rot-causing bacterial pathogens of onions.