Preliminary Studies On Endophytic Fungus In Cucumber And Other Cucurbitaceous Plants

The samples of cucumber and other common cucurbitaceous plants were collected from fields and greenhouses with different growing conditions on the outskirts of Beijing including Haidian,Tongzhou, Daxing,and Langfang of Hebei.Fungal endophytes were isolated from the plant samples and 228 strains were isolated for identification and classification.Combined morphological characteristics with the results of sequence comparison of ITS and 18S regions of rDNA,the strains fell into 13 genus.From the endophytes in cucumber plants 20 species of 11 genus were identified,including Fusarium oxysporum Schltdl., Chaetomium globosum Kunze,Epicoccum nigrum Link,Myrothecium roridum Tode,Trichoderma longibrachiatum Rifai,Trichoderma reesei Simmons,Alternaria alternata(Fr.) Keissl.,Cladosporium cladosporioides(Fresen.) de Vries,Penicillium brevicompactum Dierckx,Aspergillus ochraceus Wilh.,and others.The dominant species was Fusarium oxysporum accounting for 45.7%.The dominant species was also Fusarium oxysporum in muskmelon and towel gourd,but it was Colletotrichum sp.in water melon,and Alternaria alternata in pumpkin and gourd.In the tested samples,Chaetomium globosum and Epicoccum nigrum were only found in cucumber, Exserohilum rostratum(Drechsler) K.J.Leonard & Suggs only found in water melon and towel gourd, Curvularia lunata(Wakker) Boedijn,Curvularia interseminata(Berk.& Ravenel) J.C.Gilman,Rhizoctonia sp.only found in pumpkin,gourd and muskmelon respectively.Trichoderma longibrachiatum and Myrothecium roridum were first reported as endophytes.Epicoccum nigrum was first reported as an endophyte in cucurbitaceous plants.Statistics showed that species diversity of fungal endophytes was higher in cucumber from fields than that in cucumber from greenhouse,and species diversity of fungal endophytes was higher in cucumber from organic vagetable production base than that in cucumber from common comercial vegetable production base.The amount of endophytes was larger in upper stem than in lower stem and roots.In plate confrontation tests,one strain of Fusarium oxysporum showed obvious antagonism to Sclerotinia sclerotiorum(Lib.) de Bary,one strain of Trichoderma longibrachiatum showed obvious antagonism to several pathogens of cucumber,and some other strains showed different degree of antagonism to Fusarium oxysporium f.sp.cucumerinum Owen.Artificial inoculation tests indicated that 83.5%of strains of endophytic Fusarium oxysporum isolated from cucumber were non-pathogenic to cucumber.Inoculation and re-isolation tests proved that the Fusarium oxysporum could colonized in root and stem of cucumber, and showed some predominance.