Isolation of cucurbit bacterial pathogens affecting commercial nurseries and biological control of cucumber angular leaf spot disease's

Cucumber Angular Leaf Spot Disease, caused by Pseudomonas syringae pv. lachrymans, is a significant bacterial disease causing yield losses in cucurbit crops. This study focuses on identifying bacterial pathogens affecting cucurbits in commercial nurseries in Adana and investigating the biological control of Cucumber Angular Leaf Spot Disease using local antagonists. A total of 27 isolates, including 19 from infected cucumber seedlings and 8 from zucchini seedlings, were identified as Pseudomonas syringae pv. lachrymans, while isolates from 14 infected melon samples were identified as Pseudomonas syringae pv. syringae. In the biological control experiments, 134 local candidate antagonist bacteria were isolated from soil, aerial parts, fruits, and seeds of cucurbit crops, along with 164 antagonist bacteria taken from the laboratory's culture collection. The in vitro antimicrobial effect of 298 candidate antagonists were assessed, of which 29 showed inhibition of Pseudomonas syringae pv. lachrymans growth by forming inhibition zones. Additionally, the phosphorus solubilization potential, siderophore production, and indole-3-acetic acid (IAA) production capabilities of these 29 isolates were investigated, leading to the selection of 15 antagonists for biological seed treatments. In the first trial to investigate the efficacy of biological seed treatments against Cucumber Angular Leaf Spot Disease, 12 antagonists demonstrated disease suppression ranging from 21% to 78%. A subsequent trial confirmed effective disease suppression with five antagonists (AD 4-2, OG1-2, OG7-7, NÇ-KK, X-77) and a combination of OG1-2 and OG7-7. The successful antagonists were identified as Providencia rettgeri, Bacillus amyloliquefaciens, Bacillus mojavensis, Bacillus pumilus, and Enterococcus casseliflavus. On the basis of these results, it is concluded that these isolates can be applied to seeds for the biological control of Cucumber Angular Leaf Spot Disease. Keywords: Pseudomonas syringae pv. lachrymans, Seed treatments, IAA, Siderophore, Antimicrobial effect