Evaluation Of The Potential And Host-specificity Testing Of Pathogens As Bio-control Agents Against Microstegium Vimineum

Microstegium vimineum is an annual herbaceous grasses origin from East and Southeast Asia.Due to human activities,it was unintentionly introduced to the United States in the 20th century.Because of its high-efficiency photosynthetic efficiency and the seed with strong vital force,it rapidly invaded the eastern United States,now it has become a vicious invasive weed.Its invasion has a huge impact on the local ecology including reducing the living space of local parts of the plants,changing the soil biological composition and local soil physical and chemical properties which makes it difficult to recover ecological environment of local place where M.vimineum was controlled successfully.Currently,the control mearsurements adopted included physical,manual,biological and chemical methods,but their effects are limited.Biological control has been used for weeds successfully,but only one case was reported for biocontrol of M.vimineum.Because it lacks systematic study of natural enemies of M.vimineum,only less than ten natural enemies have been reported,some of which are serious corp diseases.Therefore,there have not been potential candidate bio-control agents available.Thus it is necessary to investigate natural disease of M.vimineum and isolate and identify pathogenic fungi,then determine the pathogenicity of those candidate isolates for biological control of M.vimineum.Then,candidate isolates are subjected to test further extensive pathogenicity and host range test to provide potential biological agents.In 2014,236 isolates were isolated from symptomatic leaves collected from different places in China,with using standard surface disinfectant isolation and single spore isolation techniques.All isolates were fungi and verified into 65 pathogens by pathogenicity test on detached M.vimineum leaves.In order to identify these 65 pathogenic fungi,morphological characters about the conidiophore and conidium were observed under the light microscope.Then,full length of nuclear ribosomal internal transcribed spacer(ITS)were amplified and sequenced.Blasting in GenBank was to find the species information of pathogens.Finally,7 genuses and 16 specieses were confirmed.There were Bipolaris oryzae,Bipolaris setariae,Bipolaris sacchari,Bipolaris sorokiniana,Bipolaris panicimiliacei,Bipolaris maydis,Bipolaris zeae,Corynespora cassiicola,Exserohilum rostratum,Curvularia lunata,Curvularia geniculata,Curvularia intermedia,Nigrospora oryzae,Nigrospora sphaerica,Phoma herbarum,Alternaria tenuissima.Spore suspensions of pathogenic fungi were sprayed on detached M.vimineum health leaves for preliminary screening.According to the median lethal concentration(ED50)and 90%lethal concentration(ED90),8 potential fungi were selected and extensively evaluated for their pathogenicity.There were 2 strains of B.setariae and B.sorokinana,and one strain of B.maydis,C.lunata,C.geniculate and P.herbarum each.According to the disease incidences in 3 disease stages and ED50,ED90,one strain of B.setariae and B.maydis each,and two strains of B.sorokinana were screened to continue the field experiment for testing their pathogenicity to M.vimineum in natural environment.In the meanwhile,host range tests in vitro about 8 pathogens were also conducted.The results showed that non-gramineous plants had no sensibility to these pathogens,but other plants had sensibilities with different extents to different pathogens.In host range tests in vivo,4 pathogens in field experiment had relatively high pathogencity to corns and some turfgrasses.However,they were relatively safe to rices and wheats,and had some pathogenicity to other farmland weeds.According to the results on the host range and bio-control effects in field,YXQST 2-1 B.setariae and MLL 1-5 B.maydis might be regarded as the most promising bio-control fungi against M.vimineum and some main farmland weed,such as Leptochloa chinensis(L.)Nees,Digitaria sanguinalis(L.)Scop and Echinochloa crusgalli(L.)Beauv..But they can not be applied in com fields and Lolium perenne L.,Cynodondactylon(Linn.)Pers.,Eremochloa ophiuroides(Munro)Hack.,Festuca elata Keng ex E.Alexeev..