Determination of efficiencies of some rhizobacteria and plant activators against Fusarium wilt disease of melon

Fusarium wilt disease (Fusarium oxysporum f. sp. melonis) is one of the major pathogens threatening the melon (Cucumis melo L.) production worldwide. The most common way that the disease is spread to plants is via infested soil, and infected seeds may also contribute to the disease dispersal. Effects of some plant growth promoting rhizobacteria (PGPR) [Bacillus subtilis subsp. subtilis (B379c), Pseudomonas aeruginosa (P07-1 ve P074), Pseudomonas sp. (P48-2)] and some plant activators (AuxiGro, Crop-Set and ISR-2000) were investigated in comparison to a commonly used fungicide (Maxim？ XL). Also, the roles of PGPR and activators in activating some enzymes (proline, catalase and peroxidase) which are critical in suppression of plant diseases, were evaluated. In seed germination experiments, particularly P07-04, and other PGPR isolates, B379c, P07-1 and P48-2 were significantly increased radicle-hypocotyl length and seed vigor index of melon seeds, compared to control. These isolates inhibited the mycelial development of Fusarium oxysporum f. sp. melonis (Fom-TR01) at the rates of 20-29%. In pot experiments, it was determined that PGPR and plant activator treatments significantly lowered Fusarium wilt disease, compared to positive control. Among PGPR isolates, P. aeruginosa (P07-1) was the most successful isolate (AUDPC 45.39%) by lowering disease severity at a rate of 35.67% (61.67% of efficiency compared to positive control). Along with disease prevention ability, this isolate also displayed a plant growth promoting effect. Among plant activators, AuxiGro was the most successful activator compared to positive control, with an efficiency rate of 49.25 % while 41.80% efficiency was obtained with Crop-Set and 35.82 % with ISR-2000. These two biotic and abiotic treatments (P07-1 and AuxiGro) were identified as the best defense enzyme (Proline, “Catalase” (CAT) and peroxidase (POX)) inducers against the pathogen. The disease suppression mechanism of PGPR isolates was determined to be associated with promoting the plant growth, as well as induced resistance