New insights into the role of phytopathogenic fungi vectored by pine bark beetles in pine decline

Abstract

The study presented was carried out in response to the alarmingly increasing number of outbreaks of bark beetles and associated fungi in European forests including Ukraine. Our study was aimed to generate new knowledge on bark beetles and understand the possible role of vectored fungi. The obtained data can contribute to the increased knowledge and will allow adequately responsing to an expected intensification of bark beetle disturbances, as well as may allow better understanding tree diseases and how to cope with them. In total, eleven ophiostomatoid fungi (Graphium sp., Leptographium sosnaicola, Grosmannia olivacea, Grosmannia penicillata, Ophiostoma bicolor, O. ips, O. canum, O. piceae, O. minus, O. nigrocarpum Graphilbum rectangulosporium) were found here in association with five species of bark beetles (Hylurgus ligniperda, Hylastes ater, Hylastes angustatus, Ips acuminatus and Ips sexdentatus) on Scots pine trees infested by bark beetles. Scots pine seedlings were inoculated with ophiostomatoid fungi and sterile medium (control) to evaluate their pathogenicity. The inoculated seedlings were examined finally 6 months later after inoculation. Inoculation with Leptographium sosnaicola, Graphium sp and O. minus produced significantly large lesions and mortality of pine seedlings. In total, all the eight fungal-inoculated species caused resin exudation and staining on the bark around inoculations in Scots pine seedlings and different rate of the seedlings decline. It can be concluded that the studied bark beetles are vectors for different functional groups of fungi including aggressive pathogens, and that ophiostomatoid fungi are the most closely associated symbionts. Moreover, high virulence fungi can help bark beetles to overcome the tree resistance and may significantly contribute to tree mortality.