The study on biocontrol of Phytophthora drechsleri, the causal agent of pistachio gummosis using some fluorescent Pseudomonads isolated from pistachio rhizospher

Phytophthora crown and root rot (Gummosis) is one of the most important diseases of pistachio trees in Iran for management of which various methods such as biocontrol have been recommended. Fluorescent Pseudomonads with the ability of producing a wide range of secondary metabolites such as different antibiotics and plant growth regulatory materials are among the most effective soil borne bacteria in biological control of plant diseases. Antagonistic fluorescent Pseudomonads were isolated from rhizosphere of infected (Gummosis) and healthy pistachio trees and their ability to control Phytophthora dreschleri was evaluated. A total of 75 Pseudomonas isolates emitting fluorescence in King B medium were obtained. In preliminary in vitro screening، seven isolates (R41، A16، A17، R14، A41، B21 and B13) showed inhibitory effect on mycelial growth of P. drechsleri based on bilateral culture test in PDA medium. The most inhibitory effect were obtained by R41 (≥15mm) and A16 (≥5mm) isolates which were selected for greenhouse tests on pistachio seedlings. The results of the greenhouse studies showed that R41 isolate exhibited greatest ability to reduce the disease severity.