The Effects of Biocontrol Bacillus and Pseudomonas Strains on Plant Growth and Biochemical Defense Mechanisms in Pistachio Seedlings Inoculated with Phytophthora Drechsleri

Introduction: Plant growth promoting rhizobacteria (PGPR) are widely used in protecting plants against pathogens in horticultural crops. Materials and Methods: In the current study, the effects of two bacterial strains, i.e. Pseudomonas fluorescens VUPF5 and Bacillus subtilis Bs96 were evaluated on plant growth and antioxidant enzymatic activities, such as GPX, PPO, and PAL, either inoculated with Phytophthora drechsleri or alone, in two pistachio cultivars of Sarakhs and Badami-Rize-Zarand. Results: The two bacterial strains reduced the mortality rate of pistachio seedlings and increased growth parameters, such as dry and fresh weights of plants’ roots, shoots, and height. The enzymatic activities and levels of phenolic compounds increased in seedlings after inoculation with the two bacterial strains and P. drechsleri. The maximum enzymatic activities were observed on the 6th day after co-inoculation with the bacterial strains and P. drechsleri. Conclusions: Pseudomonas fluorescens VUPF5 resulted in the highest levels of enzymatic activities and phenolic compounds. The highest levels of enzymatic activities and phenol contents were found in Badami-Rize-Zarand cultivar, with a highest level of resistance to P. drechsleri.