Biological Control of Phytophthora drechsleri Tucker, the Causal Agent of Pistachio Gummosis, under Greenhouse Conditions by Use of Actinomycetes

Abstract

Actinomycetes enhance soil fertility and have antagonistic activity against wide range of plant root-pathogens. These microorganisms were isolated from agricultural soils of Kerman as pure cultures. Phytophthora drechsleri Tucker, causes gummosis and root rot of pistachio trees worldwide. From 130 Actinomycetes isolates, 12 inhibited growth of the pathogen of pistachio gummosis in culture plates and four of the most active isolates exhibited biological control of the pathogen under greenhouse conditions. When plants were grown in sterile soil mix and treated both with Actinomycetes and the pathogen, the number of healthy plants increased dramatically and the symptoms on diseased plants were less severe in comparison with seedlings treated with the pathogen alone. From the collected data it was well conclusive that in greenhouse tests, soil applications of Actinomycetes controlled causal agent of root rot of pistachio seedlings. Antifungal activity was of fungicidal type on the pathogen mycelia. From the stand point of biotechnological goals, the results indicate that the active isolates can be investigated for use as biofertilizers, biofungicides and use in future development of recombinant DNA in pistachio trees bearing elevated resistance to gummosis. Field trials of the active isolates are under investigation