Effect of rhizosphere bacteria on bacterial seedling blight disease caused by Acidovorax citrulli in melon

In this thesis study, the possibilities of using rhizosphere bacteria in the biological control of Melon Bacterial Seedling Blight caused by Acidovorax citrulli were investigated in in vitro and in vivo conditions. For this purpose, 241 candidate antagonists were isolated from soil samples taken from the rhizosphere of melon, watermelon, tomato, eucalyptus and pine. 157 bacterial isolates from our laboratory's collection, with proven antagonistic effects on different pathogens as well as rhizosphere bacteria, were included in the study. The antibacterial effects of a total of 398 candidate antagonist bacteria were examined by double culture test and it was determined that 38 bacterial isolates had antibacterial activity by creating a 0.3-7.7 mm inhibition zone. The in vitro antagonistic action mechanisms of these bacteria (ability to produce siderophores, ability to solubilize phosphorus, and amount of indole acetic acid production) were examined. While 15 of these isolates were determined to produce siderophores, it was determined that none of the isolates could dissolve phosphorus. On the other hand, it was determined that 11 isolates produced high amounts (156.8-170.5 μg/ml) of IAA, a growth hormone. As a result of in vitro tests, 8 isolates with antibacterial effects and multiple mechanisms of action were selected and their effects on disease severity were investigated with biological seed applications. In the first seed trial, 8 applications suppressed disease severity by 0.48-39.45%. In the second seed trial established with the two most successful isolates, Y90 prevented the disease at a rate of 46.37%, while this rate was 18.97% in Y28. In diagnostic studies carried out using the MALDI TOF MS method, the isolate coded Y28 was identified as Providencia rettgeri and the isolate coded Y90 was identified as Bacillus amyloliquefaciens plantarum. According to these results, it was concluded that biological seed applications with Providencia rettgeri (Y28) and Bacillus amyloliquefaciens subsp. plantarum (Y90) could be successful in the biocontrol of Seedling Blight Disease in melons