Identification and molecular characterization of bacterial fruit blotch disease agent acidovorax citrulli and biological control of disease by antagonistic bacteria

Watermelon seedling blight and fruit blotch disease, caused by Acidovorax citrulli, is one of the most significant diseases of watermelon. In this study, 108 bacterial isolates were collected between 2009 to 2012 years in major watermelon and melon producing areas in the Eastern Mediterranean Region and identified by biochemical and molecular methods. Genetic relations between isolates were determined by using AFLP-PCR method. 108 bacterial isolates obtained from diseased plants were identified as Acidovorax citrulli according to biochemical and molecular tests. Molecular analyses of bacterial isolates revealed that Turkish isolates come from two different inoculum sources, thus it's likely that the inoculum sources might have been spreaded through seed trading. In this study, biological control of the disease was also investigated by using antagonistic bacteria. Among the 322 putative bacterial isolates, 54 antagonistic bacteria were suppressed the disease agent in vitro dual culture tests. 14 antagonist bacterial isolates were chosen and applied as seed treatments. Three isolates suppressed disease incidence by 10-94% and disease severity by 10-96% in vivo conditions. Three bacterial isolates were further tested in greenhouse and field conditions. Antagonist bacterial isolates (Antg-12, Antg-97 ve Antg-101) were suppressed disease development by 20-49 % in greenhouse conditions, by 7-27% in field conditions. We recommend that biological control agents should be applied as seed treatment rather than foliar spraying for biological control of the disease.