Identification of rhizospheric fluorescent pseudomonads of cucumber and evaluation of their antagonistic potential as biocontrol agents

Fluorescent pseudomonads are important group of plant growth promoting bacteria that can improve the plant growth and restrict or suppress phytopathogens directly or indirectly. The aim of this study was to obtain fluorescent pseudomonads with efficient antagonistic activities. For performing this research, a total of 120 bacterial isolates belonging to Pseudomonas fluorescens and P. putida were isolated from different cucumber rhizospheric soil in Hamedan province. Then, the isolates were screened for their plant growth promoting traits and antibacterial activity. These isolates also were screened against Pseudomonas syringae pv. lachrymans. So, five antagonistic strains (BSU390, BSU630, BSU205, BSU161 and BSU391) with inhibition diameter >7 mm were selected. The range of inhibition diameter for these isolate was 7.66 to 22 mm. Also, during in vivo study, the strains were evaluated for their effect in suppressing disease development in terms of area under disease progress curve (AUDPC) and increasing biomass of cucumber. Accordingly, BSU390, BSU205, and BSU630, showed high biocontrol efficacy. During the sole application, the strains significantly (P ≤ 0.05) increased plant height and dry matter compared to non-bacterized control. Hence, the study shows that these isolates have potential use in cucumber bioprotection, as PGPR or in an integrated disease management; whose effectiveness under a variety of field conditions should be investigated.