Xishuangbanna Vanilla Growing Areas Of Biocontrol Screening

ABSTRACTMicroflora of soil and plant of vanilla fragrans at different sites in Xishuangbanna of Yunnan province and the relationships between the microflora of Vanilla fragrans with the root rot and Fusarium wilt of Vanilla fragrans were analysed. The strains with potential antagonistic to targets pathogens were selected based on the assay in vitro et in vivo for biocontrol of root diseases of Vanilla fragrans and other important diseases in plant. Thirty-four strains of bacteria, fifty-eight strains of actinomycetes and one hundred and fifty-four fungi isolates in soil, forty-two endophytic bacteria and seventeen fungal endophytes were isolated from eleven soil samples and nine plant samples of vanilla fragrans collected in different areas of Xishuangbanna. The tendency showed that the bacteria were the dominant microflora. The dominant isolates of fungi were Fusarium, this is consistent to the results of other researches on the pathogens of root rot of Vanilla fragrans. There was no relationship between the other dominant microflora in all the samples with the incidence of the root diseases in Vanilla fragrans. The pathogen of root rot of Vanilla fragrans was Fusarium because the dominant strains were most Fusarium in diseased soils and diseased plants. Sixty-seven bacteria and fifty-eight strains of actinomycetes were assayed in vitro for antagonism to target pathogens, the results showed that thirteen strains of bacteria and three actinomycetes which existed in all the samples had strong antagonism. On the basis of extracting chitinase, two strains of actinomycetes (087, 105) were selected because of their colonizing on the target pathogens. Morphological observation with a light microscope showed that the hyphae of F. oxysporum f.sp. vasinfectum and Verticillium dahliae were fractured or destroyed and the dormant structure of them were lysis. The observation with a scanning electron microscope demonstrated that the mycelium of 105 bound the hyphae of F. oxysporum f.sp. vasinfectum, some chlamydospores of the target pathogens were lysis. Antagonism to F. oxysporum f.sp. vasinfectum and F. oxysporum f.sp.cucumerinum of strain 087 were better than strain 105, while the examinations to Verticillium dahliae were opposite. Strain 087 is Glaucus and strain 105 is Albosporus of Streptomyces.