Studies Of Population Diversity On Endophytic Fungi Of Tobacco And Selection Of Biocontrol Endophyte To Tobacco Brown Spot Disease

In this study,the biodiversity and dynamic distribution rule of population of endophytic fungi in roots,stems and leaves of nine tobacco cultivars were studied at different growth phases,through two years of repeated experiments from 2007 to 2008 in Henan Province.From this study we have cleared about the composition and distribution of tobacco endophytic fungi,established endophyte resource library of tobacco, examined the antagonistic activity of the endophyte against Alternaria alternata in laboratory and selected out some strains of high antagonistic activity to Alternaria alternate,which have established the good foundation of biological control research to tobacco brown spot disease.At the same time,we have studied the relationships of tobacco brown spot pathogen and endophytic Alternaria alternate.The detailed results are as follows:1.Diversity of endophytic fungi.977 strains were studied by promoting sporulation and morphological identification.There are 943 isolates sporulated,occupying to 96.52 percent of the total strains,belonging to 15 genera.They are Alternaria Nees, Chaetomium Kunze,Penicilium Link,Fusarium Link.,Trichotderma Pers.,Aspergillus P. Micheli ex Link:Fr.,Nigrospora Zim.,Colletotrichum Gorda,Phoma Sacc.,Bipolaris Shoemaker,Trichothecium Link,Exserohilum K.J.Lenoad Suggs,Phyllachora Nitschke ex Fuckle,Curvularia Boedijn and Pestalotiopsis Steyaert.24 species were identified from 943 sporulated isolates,which are Alternaria alternate(Fr.:Fr.)Keissler,Alternaria bataticola(I kata) Yamamoto,Alternaria zhengzhouensis T.Y.Zhang,Chaetomium funicola Cooke,Chaetomium succineum L.M.Ames,Chaetomium raii G.Malhotra & Mukerji,Chaetomium aureum Chives,Chaetominum bostrychodes Zopf,Penicilium digitatum(Pers.:Fr.) Sacc.,Fusarium moniliforme Sheldon,Fusarium stoveri Booth, Trichoderma longibrachiatum Rifai,Aspergillus.niger Tiegh.,A.fumigatus Fres, Nigrospora sphaerica(Sacc.) Mason,Colletotrichum Gloeosporioides(Penzig)Penzig et Saccardo,Phoma epicoccina Punithalingam,Tulloch & Leach,Bipolaris sorokiniana (Sacc.) Shoemaker,Exserohilum rostratum(Drechler) Leonard & suggs,Trichothecium roseum(Pers:) Link.,Curvularia lunata(Waker) Boedijn,Phyllachora nicotiae W.Han, Pestalotiopsis nicotiae W.Han.The occurency frequency of Alternaria Nees and Chaetomium Kunze were 22.42%and 16.27%,they were the dominant population of endophytic fungi in tobacco.34 isolates did not sporulate under ordinary conditions.2.The dynamic distribution rule of endophytic fungi at different growth phases of Tobacco.From seedling to maturity phase,the type and the amount of endophytic fungi isolated increase in the order:seedling phase＜rosette phase＜vigorous growth phase＜mature phase.During vigorous growth phase and mature phase,all the nine genera of fungi were detected,and the populations increased sharply from rosette phase.3.The distribution rule of endophytic fungi in tobacco roots,stems and leaves:977 strains of endophytic fungi were isolated from the roots,stems and leaves of tobacco.The leaves had the greatest population of endophytic fungi,followed by in stems and roots.174 strains of 7 genera were isolated from roots,365 strains of 11 genera from stems,and 438 strains of 14 genera from leaves.The results showed that the quantity,population,and distribution of the endophytic fungi varied in different tissues of tobacco.4.Annual change of tobacco endophytic fungi:Compared the endophytic fungi isolated from tobacco in 2007 and 2008,we found that the dominant species is relatively stable,which can be detected in the two years.Individual endophytic fungi only be isolated in one year.The results show that the endophytic fungi of tobacco were different in different years.5.The results of antagonism showed that the endophyte strains had different ability against Alternaria aIternata.Form 977 fungal strains,329 bacterial strains and 11 actinomycete strains,2 fungal strains,4 bacterial strains and 1 strains of actinomycete were screened,the rate of antagonism was 70%above,which had been proved no pathogenicity to tobacco.6.Study of pathogenicity of endophytic Alternaria alternata:the dominant endophytic Alternaria species is same as the pathogenic species of tobacco brown spot disease The results of inoculation showed that some isolates of endophytic Alternaria alternata are no pathogenicity to tobacco,some have weak or obvious pathogenicity.Those pathogenic strains have the characteristis of a long-term potentia in different tissues of tobacco.When the environmental and plant conditions are suitable for disease,symptoms will appear.The results have great guiding significance for the control of tobacco brown spot disease.