Watermelon Fusarium wilt, caused by Fusarium oxysporum, leads to significant yield loss in watermelon crops. This study aimed to isolate Pseudomonas strains with strong antagonistic effects against watermelon fusarium wilt and to evaluate their plant growth-promoting effects. The antibacterial efficacy of various strains against a range of pathogens was tested and their morphological, physiological, biochemical, genetic characteristics and ability to promote plant growth were assessed. A total of 525 bacterial strains were screened, identifying three biocontrol strains——Pseudomonas aeruginosa P2-1, P3-1 and P3-4——that significantly inhibited the growth of Fusarium oxysporumf. sp. citrulli. These strains demonstrated the ability to fix nitrogen, solubilize organic and inorganic phosphorus, produce siderophores, and exhibit protease and lipase enzyme activities, which contributed to increased plant height, stem diameter, chlorophyll content, and both fresh and dry weights of aboveground and underground parts of watermelon seedlings. Additionally, the biocontrol efficacy of these strains against watermelon fusarium wilt in pot experiments ranged from 62.29%~63.93%. Membership function analysis ranked their disease resistance and growth promotion effects in the following order: P3-4, P3-1, P2-1, CK. Strain P3-4 shows potential as a biological control agent for managing watermelon fusarium wilt and enhancing seedling growth, contributing to the sustainable and efficient production of watermelon and providing a foundation for the development of biological control agents against this disease.
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