Characterization and identification of Burkholderia gladioli causing stalk rot of sweet corn in Thailand

Stalk rot disease is becoming an important disease in sweet corn crops because it causes significant yield losses of the crop. In July 2022, typical symptoms of stem rot were observed in fields of Mae Hia Agricultural Research, Demonstration and Training Center in Chiang Mai province of Thailand. The symptoms exhibited by affected crop included circular water-soaked lesions, rot and necrotic tissue at the base of the stalk. Koch's postulates were fulfilled with reisolation of the inoculated strain from the inoculated tissues, and confirmation was obtained by phenotypic characters and 16S rRNA sequences. The isolated colony on nutrient agar was cream-coloured, circular, with a convex elevation, entire margin and smooth surface; the optical character was translucent and exuded a yellowish pigment that diffused in the nutrient agar, gram-negative, lacked arginine dihydrolase, occurrence of the oxidase and catalase reaction. The strains were able to utilize d-galactose and glucose but were unable to utilize d-maltose, d-cellobiose, d-fructose, d-mannose, mannitol, lactose and sucrose. The strains showed positive results for gelatine liquefaction test, citrate utilization and casein hydrolysis, but starch hydrolysis and indole production were negative result. These characteristics are the same as those described previously for Burkholderia gladioli. Disease severity in sweet corn was 43.8%, with infections showing spots with dark margins and soft rot on mature leaves and flag leaves. Disease severity in waxy corn and maize were 21.9% and 15.6%, respectively, showing a few light or dark brown spots at the infection sites. Therefore, this represents the first report of leaf stripe and stalk rot disease in sweet corn in Thailand.