Study On Biocontrol Of Southern Blight On Houttuynia Cordata Thunb By Bacillus Spp

In this research,the Bacillus isolated from the rhizosphere and leaves of Houttuynia cordata Thunb,was used for controlling southern blight.And its identification,population dynamics in soil,antibacterial spectrum, biological characteristic and mechanism were studied. The results are as follows:1,More than four hundreds bacillus were isolated from the rhizosphere and leaves of Houttuynia cordata Thunb.43 antagonistic strains were selected from them,which showed antifungal activity to the Sclerotium rolfsii Sacc in dual culture.4 strains inhibited the Sclerotium rolfsii Sacc strongly, were further assessed for their ability to control the pathogen in pot inoculation experiments.Finally, B8 was selected as biocontrol agent, which inhibited the Sclerotium rolfsii Sacc to 67.7% and 56.8% in dual culture and pot inoculation experiments.2,Population dynamics of the strain B8 marked with Rifampicin in the rhizosphere of Houttuynia cordata Thunb were investigated.The results showed that the rifampicin resistant mutants of the strain B8 were able to colonize in the rhizosphere of Houttuynia cordata Thunb.The colonization of the B8 reached 1.85 times as much as original population on the 7th day after inoculation,decreased to 20.8% after treated 15 days.3,Strain B8 was identified as Bacillus subtilis Cohn based on morphological, physiological and biochemical methods as well as on 16S rDNA sequence analysis.The colonies of strain B8 on NA plate were round, irregular edge,rugous,white and opaque. Light micrographs revealed that cells of strain B8 were rod shaped(0.8μm×3.2μm),gram positive,and formed endospore(0.7μm×1.7μm)4, B8 were cultured in 6 kinds of medium (BPY, YT, YPG, YSP, LB,NA).The best medium of them for B8 growth was YPG, the second was YSP, and the worst was NA. The best medium for producing antagonistic substance was YSP, the second was NA,and the worst was BPY. The optimal conditions for B8 growth were 35℃, pH7.0,culture time 48h with 20ml medium in 250ml triangular flask;for producing antifungal substance was 30℃pH7.0,culture time 48h with 20ml medium in 250ml triangular flask.5,Mechanisms of antifungal action of the strain B8 were studied.The volatile metabolites of B8 were able to against the growth of mycelia. The forming and germination of sclerotium were inhibited by the culture filtrate of B8.In light microscopic observations,the hyphae appeared tips swollen,malformed, ruptured, and emptied after controlled by the culture filtrate of B8.The antibiotics were sensitive to high temperature, alkali and acid. The antifungal productions were isolated from B8.The result showed they were proteins.The molecular weights of the antifungal proteins were determined as 14.0 to 60.4kD by SDS-PAGE.6,Inhibitory effects of strain B8 on 5 kinds of pathogens were tested.The results showed strain B8 could reduce the growth of 5 kinds of pathogens by>55%.The antifungal productions of B8 inhibited pathogens widely. B8 showed the highest inhibition on phoma Cyathula(71.43%),the lowest inhibition on Rhizoctonia zeae Voorhees(55.56%).