Viruses ofHeterobasidion parviporumpersist within their fungal host during passage through the alimentary tract ofHylobius abietis

Abstract

SummaryHeterobasidion annosum(Fr.) Bref.sensu latois an important fungal parasite of coniferous trees throughout the temperate regions of the world. Approximately 15% ofHeterobasidionisolates are infected by dsRNAviruses, which are considered as obligately intracellular and transmit vertically into both basidiospores and asexual conidia. Insects such asH. abietisand its larvae feeding on wood colonized byHeterobasidionfungi may carryHeterobasidionconidia and hyphae. In this study, we usedH. abietisas a model species to reveal whetherHeterobasidionviruses resist in their fungal host passing through the digestive tract of insects that may potentially serve as disseminators of fungal propagules.Pinus sylvestrisbranches were inoculated by three different strains ofHeterobasidion parviporum, hosting taxonomically diverse virus species:HeterobasidionRNAvirus 2, HetRV4 and HetRV6. Then, the inoculated branches were fed toH. abietisinsects, and beetle excrements were investigated forHeterobasidioninfections. All the inoculated fungal strains survived passage through the alimentary tract of the insects (survival rate 25–80%). The passage rates of the viruses inside their hosts varied considerably, ranging from 0 to 67%. Two different mycoviruses, HetRV2 and HetRV6, survived the intestinal passage of their fungal host, while the virus species HetRV4 was detected among none of the fiveH. parviporumisolates retrieved from insect faeces. The relative stability of fungi harbouring viruses suggests that if viruses are to be used for biological control againstHeterobasidionspecies, it is likely that insect feeding does not considerably decrease the virus effect, but might instead enhance short‐range dispersal of the viral biocontrol agent.