Ophiostomatalean fungi associated with Polygraphus bark beetles in the Qinghai-Tibet Plateau, China.

Climate change has exacerbated outbreaks of forest pests worldwide. In recent years, bark beetles have caused significant damage to coniferous forests of the Northern Hemisphere. Polygraphus bark beetles are widely distributed secondary pests. Recently, tree mortality caused by these beetles on the Qinghai-Tibet Plateau has been increasing; however, few studies have focused on their fungal associations. In the present study, we explored the diversity of ophiostomatalean fungi associated with these beetles on the north-eastern and southern Qinghai-Tibet Plateau. We isolated 442 ophiostomatalean strains from adult beetles and their fresh galleries, specifically targeting Polygraphuspoligraphus and Polygraphusrudis infesting Piceacrassifolia and/or Pinusgriffithii. Based on phylogenetic and morphological features, we assigned the 442 strains to 16 species belonging to Grosmannia spp., Leptographium spp. and Ophiostoma spp. Amongst these, Ophiostomamaixiuense and Ophiostomabicolor were the most frequently isolated species, accounting for 20.8% and 18.1% of the total number of ophiostomatalean assemblages, respectively. By comparing their fungal communities, we found that the different patterns of fungal assemblages of bark beetles from the north-eastern and southern Qinghai-Tibet Plateau may be influenced by biogeographic barriers and host tree species. The results of this study enhance our understanding of bark beetle fungal assemblages, especially Polygraphus, on the Qinghai-Tibet Plateau, with implications for forest management under changing climate.