Characterization of Acidovorax avenae subsp citrulli strains isolated from watermelon and melon fields in Israel

Acidovorax avenae subsp. citrulli (Aac) is the causal agent of bacterial fruit blotch (BFB) of cucurbits. BFB gained attention with outbreaks in watermelon fields in the Mariana Islands and Florida in the late 80’s. Aac was also found to cause disease on other cucurbits such as cantaloupe, honeydew and pumpkin. In Israel, the bacterium was detected in imported seeds and in diseased seedlings grown from imported seeds during the 90’s. Although the occurrence of BFB in Israel has been sporadic, in 2003, the disease caused yield losses in a few fields, where plants were produced from imported seeds. Here we report the isolation of several strains from diseased watermelon and melon plants. The strains were confirmed as Aac using Koch postulates, followed by GC-FAME analysis and sole carbon substrate utilization profiles. Differences were found among strains in their pathogenicity on watermelon, melon and cucumber varieties. Also, several differences were observed in carbon substrate utilization profiles. Aac strains isolated from similar hosts shared the most similarities in pathogenicity and carbon substrate utilization profiles. Walcott et al previously suggested the existence of at least two Aac groups, one including strains from cantaloupe and pumpkin, the other representing the typical BFB-causing strains. Results from this study indicate that both groups may have been imported to Israel.