Toxoflavin produced by Burkholderia glumae causing rice grain rot is responsible for inducing bacterial wilt in many field crops

Severe wilt symptoms similar to bacterial wilt caused by Ralstonia solanacearum were observed in tomato, hot pepper, eggplant, potato, perilla, sesame, and sunflower in 2000 and 2001 in Korea. From diseased crops at 65 different locations, we obtained 106 isolates that produced green pigment on CPG medium; 36 were isolated from discolored rice panicles. The causal pathogen was identified as Burkholderia glumae based on its biochemical characteristics, fatty acid methyl ester analysis, and 16S rRNA gene sequence. Nine representative isolates produced toxoflavin, as determined by electrospray ionization mass spectrometry using a direct inlet system and TLC analyses, and caused bacterial wilt on tomato, sesame, perilla, eggplant, and hot pepper. However, BGR12, a wild-type isolate lacking toxoflavin production and toxoflavin-deficient mutants generated by Tn5lacZ failed to cause bacterial wilt on those five field crops. Cells of B. glumae and synthetic toxoflavin caused wilt symptoms on field crops, demonstrating a lack of host specificity. Synthetic toxoflavin caused wilt symptoms on tomato, sesame, perilla, eggplant, and hot pepper at 10 mug/ml concentration 1 day after treatment. This is the first report of bacterial wilt on various crops caused by B. glumae, and our results clearly demonstrate that toxoflavin is a key factor in wilt symptom development.