Pathogenicity evaluation of pathogenic fungi causing of oak tree dieback in Kermanshah province

Oak dieback is one of the most important diseases that presently affects the Zagros oak forests (Northwest to Southeast of Iran). The presence of Paecilomyces formosus, Biscogniauxia mediterranea and Neoscytalidium novaehollandiae associated with oak trees that show dieback and declining symptoms in the forests of Kermanshah province and the molecular and pathogenic characteristics of these pathogenic isolates were investigated. In molecular analysis using blast search tools, all three pathogens showed homology of 100% with the mentioned species in the GenBank. Pathogenicity test revealed that all isolates of these three pathogens were capable of producing cancers on detached branches and inoculated seedlings of oak trees. Our results showed that all three species obtained from oak trees could produce cankers on excised branches of other trees. In comparison with pathogenicity on two-years-old seedlings under drought stress, there was a significant difference between the three species in terms of the rate of disease progression, so that B. mediterranea caused symptoms on seedlings inoculated under drought stress in a shorter time. P. formosus caused symptoms in longer period on the inoculated seedlings than the other two species. After inoculation, all cankers that extended upward and downward from the point of inoculation were evident on stems of all inoculated seedlings. Re-isolation was performed, and isolates were compared to original cultures providing evidence for fulfilling Koch’s postulates. Investigation of the effect of temperature on radial growth of pathogenic species showed that all three species are thermophilic fungi, which may be related to warming and drought.