An Evaluation of Four Plant Growth-Promoting Rhizobacteria (PGPR) and Their Effects on Controlling Crown and Root Rot of Pistachios Caused by Phytophthora Parsiana

Introduction: The use of plant growth-promoting rhizobacteria (PGPR) is a promising method in sustainable agriculture and can be an efficient alternative to chemical pesticides. Materials and Methods: In this study, antagonistic features of four bacterial strains, including Pseudomonas fluorescens VUPF5, P. fluorescens T-17, Bacillus subtilis V1, and B. subtilis B96 were investigated. In addition, their effects on crown and root rot of pistachios (gummosis), caused by Phytophthora parsiana, were assessed. Besides, different populations (104, 106, 108 CFU/ml) of bacterial strains on the fresh and dry shoot and root weight of pistachios in the Sarakhs cultivar were evaluated. Results: The results showed that all bacterial strains had remarkable antagonistic effects and were capable of controlling pistachio gummosis under greenhouse conditions. P. fluorescens VUPF5 had the strongest effect among the selected strains under laboratory and greenhouse conditions, with a 70% reduction in the mortality rate. Upon a reduction in the initial inoculated population of the bacteria, their growth-promoting effects on growth factors in pistachio seedlings decreased. Conclusion: Research should be carried out on the efficiency of the selected rhizobacteria strains by utilizing them under field conditions to evaluate their effectiveness in interaction with other microorganisms.