Differential patterns of ophiostomatoid fungal communities associated with three sympatric Tomicus species infesting pines in south-western China, with a description of four new species

Abstract

Bark beetles and their associated fungi, which cause forest decline and sometimes high mortality in large areas around the world, are of increasing concern in terms of forest health. ThreeTomicusspp. (T.brevipilosus,T.minorandT.yunnanensis) infect branches and trunks ofPinusyunnanensisandP.kesiyain Yunnan Province, in south-western China.Tomicusspp. are well known as vectors of ophiostomatoid fungi and their co-occurrence could result in serious ecological and economic impact on local forest ecosystems. Nonetheless, knowledge about their diversity, ecology, including pathogenicity and potential economic importance is still quite rudimentary. Therefore, an extensive survey of ophiostomatoid fungi associated with theseTomicusspecies infestingP.yunnanensisandP.kesiyawas carried out in Yunnan. Seven hundred and seventy-two strains of ophiostomatoid fungi were isolated from the adult beetles and their galleries. The strains were identified based on comparisons of multiple DNA sequences, including the nuclear ribosomal large subunit (LSU) region, the internal transcribed spacer regions 1 and 2, together with the intervening 5.8S gene (ITS) and the partial genes of β-tubulin (TUB2), elongation factor 1α (TEF1-α) and calmodulin (CAL). Phylogenetic analyses were performed using maximum parsimony (MP) as well as maximum likelihood (ML). Combinations of culture features, morphological characters and temperature-dependent growth rates were also employed for species identification. Eleven species belonging to five genera were identified. These included six known species,Esteyavermicola,Leptographiumyunnanense,Ophiostomabrevipilosi,O.canum,O.minusandO.tingensand four novel taxa, described asGraphilbumanningense,O.aggregatum,SporothrixpseudoabietinaandS.macroconidia. A residual strain was left unidentified asOphiostomasp. 1. The overall ophiostomatoid community was by far dominated by three species, representing 87.3% of the total isolates; in decreasing order, these wereO.canum,O.brevipilosiandO.minus. Furthermore, the ophiostomatoid community of each beetle, although harbouring a diversity of ophiostomatoid species, was differentially dominated by a single fungal species;Ophiostomacanumwas preferentially associated with and dominated the ophiostomatoid community ofT.minor, whereasO.brevipilosiandO.minuswere exclusively associated with and dominated the ophiostomatoid communities ofT.brevipilosusandT.yunnanensis, respectively. Eight additional species, representing the remaining 12.7% of the total isolates, were marginal or sporadic. These results suggested that sympatricTomicuspopulations are dominated by distinct species showing some level of specificity or even exclusivity.