Induction of plant defense response against Phytophthora crown and root rot in pistachio by Pseudomonas fluorescens strains

Activities of thirty bacterial strains obtained from plants rhizosphere in different areas against Phytophthora drechsleri were assessed through in vitro and greenhouse experiments. Dual culture and extracellular metabolites tests were used in in vitro assays. The bacterial strains inhibited growth of P. drechsleri, the highest inhibition zones was belonged to T17-4 strain with 61.904% in dual culture and VUPF760 strain with 57.87% in cell free metabolites tests. The highest and lowest reduction rates of disease severity were belonged to VUPF760 and VUPF506 with 68.75 and 16.66%, respectively. In the second section of the study, the ability of bacterial strains to induce peroxidase, polyphenol oxidase, phenylalanine ammonia lyase and phenolic compounds in pistachio seedling was investigated 3, 6, 12 and 24 days after inoculation. Bacterial strains increased enzyme activities that reached the maximum levels 6 days after inoculation with pathogen. The highest level of phenolic compounds was observed at 6 days after pathogen inoculation in treatments of bacterial strains and Ph. drechsleri compared with control. Induction of resistance in plants even 24 days after post-treatment with bacterial strains was effective for induction of more durable resistance compared to other activators of plant defense system. The ability of bacterial strains to increase enzymes activities and levels of phenolic compounds may be some of the mechanisms responsible for their biocontrol activities. VUPF760 strain showed the highest increase enzymes activities and levels of phenolic compounds.