Diversity Of Fungal Endophytes In Ageratina Adenophora And The Dynamics In Surrounding Environment

In recent years,biological invasion has been a global problem and it has been becoming a hot research topic worldwide.The invasion of Ageratina adenophora in southwest China is not only a serious threat to the local ecological balance but also caused great economic losses.Some researchers proposed a hypothesis named"Accumulation of local pathogens",which suggests that invasive plant can gain an indirect competitive advantage through accumulating local plant pathogens.But for now,it is unknown about local fungal pathogens which inhabit A.adenophora as endophytes.We suppose that these fungi may be released into air as spores from the leaves of A.adenophora,and then infect native plants in the surrounding environment.Moreover,the decaying leaves on the ground may release those fungi to infect native plants through soil and water flow.In this study,the endophytic fungi of roots,stems and leaves of six populations of A.adenophora in Yunnan,and the fungi in the surrounding air and soils in these invaded areas were investigated.Meanwhile,fungi in air of uninvaded areas in Yunnan were also detected.In total,4439 fungal colonies were categorized morphologically.ITS genes of 1177 representatives were successfully sequenced and distinguished into 200 operational taxonomy units(OUTs)at the level of 97%similarity by traditional culture.ITS genes were successfully distinguished into 4216 operational taxonomy units(OUTs)at the level of 97%similarity by high-throughput sequencing.In addition,fungi in roots,stems,fresh and rotten leaves,and rhizosphere soils of A.adenophora were also determined by the high-throughput sequencing technology.The obtained data were used to analyze the dynamic distribution of endophytic fungi of A.adenophora in the surrounding environment and several following conclusions were achieved:1.The distribution of endophytic fungi varied among different tissues of A.adenophora.Genus Colletotrichum is the predominant endophytic fungi in leaves,with an isolation percentage of 55.09%;genus Didymella is the predominant endophytic fungi in stems,with an isolation percentage of 31.85%;Fusarium is the predominant endophytic fungi in roots,with an isolation percentage of 37.50%.Genus Diaporthe is numerically dominant in roots,stems and leaves of A.adenophora.2.The endophytic fungi in the aboveground part of A.adenophora may transmit by air and those in the underground part of A.adenophora may transmit by soils.On one hand,OTU overlaps are higher between fungi from air with those from leaves than either with those from stems or with those from roots.Moreover,fungi in A.adenophora had a lower OTU overlaps with fungi obtained from air in the uninvaded region than with those in the invaded region of A.adenophora.In addition,numerically dominant foliar fungi including Colletotrichum,Diaporthe,Didymella and Alternaria showed a higher percentage in air than in soils.On the other hand,both OTU and strain number overlaps of fungi from soils with those from roots are higher than both with those from stems and with those from leaves.Moreover,numerically dominant Fusarium in roots showed a higher percentage in soils than in air.These results showed that the endophytic fungi in the leaves of A.adenophora may transmit by air and those in the roots may transmit by soils.3.Some saprophytic fungi may spread through the rotten leaves.The dominant endophytic fungi Alternaria in the leaves of A.adenophora are rare in the surrounding air and soils but significantly dominant in rotten leaves of A.adenophora.Maybe these fungi are not able to survive the soil and air environments therefore it was supposed that they are able to horizontally transmit to A.adenophora through rainwater and through direct contact with seedlings.The transmission by rotten leaves is likely to be a different pathway from soil transmission and airborne transmission.4.There is a great difference in species structure revealed by traditional culture and high-throughput sequencing.Fungi in roots,stems,fresh and rotten leaves,and rhizosphere soils of A.adenophora revealed by the high-throughput sequencing technology are extremely higher in species number and diversity than by traditional culture methods.The numerically dominant fungi determined by the high-throughput sequencing technology are Rachicladosporium,Agaricus,Strelitziana,Alternaria,Clitopilus,Delicatula,Tetracladium and Tomentella,but those obtained by traditional culture methods are Colletotrichum,Diaporthe,Didymella,Alternaria,Fusarium,Trichoderma and Penicillium.Again the OTU overlaps of fungi from roots with those from soils are still highest and support that the fungi in roots may transmit by soils,a conclusion obtained by traditional culture methods.