Study On The Species And Relationship Between The Associated Fungi Of Dendroctonus Valens LeConte And The Endophyte Of Host Trees

Dendroctonus valens LeConte(red turpentine beetle,RTB)is one of the major alien forest quarantine pests,which caused severe damages to pine forests after invading China.With the associated fungi carrying on the body surface,RTB and the fungi can cause composite damages.In 2017,our research group discovered a breakout of RTB in Chifeng,and the RTB began to damage a new host tree species,Pinus sylvestris var.mongolica besides Pinus tabuliformis.RTB associated fungi entered into the host phloem with RTB body surface,and then they competed with trees endophytes for nutrients and habitats.The microenvironment of the host trees and the influences on RTB infection mechanisms were unclear.To clarify the relationship between the two,this research took RTB body,gallery,and the host tree species phloem as primary research materials;RTB associated fungal and endophytes of host tree as the research objects.This study analyzed the effects and mechanism of host tree endophyte fungi on RTB from the community level and species level.The main results are as follows:1.The species of associated fungi in the new habitat and new host tree species were identified.There are four species of associated fungi,including Leptographium procerum,Ophiostoma minus,Ophiostoma ips,and Sydowia polyspora.This study isolated all four species from P.tabuliformis,and only the first three species from P.sylvestris var.mongolica.2.This study isolated and identified the structure of the RTB gallery's fungal community.Twenty-eight species of fungi were isolated from the RTB's gallery,which belonged to 1 phylum,7 classes,11 orders,15 families,and 20 genera,Saccharomycopsis sp.is the main species,followed by the four species of RTB associated fungi(L.procerum,O.minus,O.ips,and S.polyspora).3.The endophytic fungal communities of host species and potential host tree species were identified and compared.Twenty-nine species of endophytic fungi were isolated from the host and potential host tree species,belonging to 2 phyla,6 classes,10 orders,18 families,and 19 genera.High-throughput sequencing results showed that the endophytic fungal communities of P.sylvestris var.mongolica and Larix gmelinii were very similar at the phylum level,with Basidiomycetes(>80%)dominating,while Ascomycetes(>90%)dominating in P.tabuliformis.4.The endophytic bacterial communities of host species and potential host tree species were identified and compared.High-throughput sequencing results showed that 121 species of endophytic bacteria were isolated from L.gmelinii phloem,mainly in Proteobacteria(>90%).Two hundred one species of endophytic bacteria were isolated from P.tabuliformis,mostly in Actinomycetes(>40%)and Proteobacteria(>30%).One hundred forty-five species of endophytic bacteria were isolated from P.sylvestris var.mongolica,mostly in Proteobacteria(>65%).5.The relationship between RTB host tree's endophytic fungi and the RTB associated fungi was determined.Their growth rate was measured,and the growth rate of RTB associated fungi were higher than all the endophytic fungi.Pochonia bulbillosa and Phialocephala sp.had significant inhibitory effects on four species of RTB associated fungi.This paper studied the community structure of RTB associated fungi both in a new habitat and new host tree species,as well as the endophyte community structure of both host and potential host tree species,compared to the difference of endophytic microorganism community between the host and potential host tree species.By dual culture assays,analyze the feature of the endophytic microorganism community of host tree species,which is suitable for RTB,identify the potential biocontrol fungi.This work would provide scientific reference for RTB's biological control and comprehensive treatment.