Screening Of Antagonistic Strains Against Plasmodiophora Brassicae And Development Of Seed Coating

Plasmodiophora brassicae of cruciferous vegetables is a very serious hazard soil-borne diseases. This disease usually infects plant roots causing severe root rot and even the whole plant of plants dead and results in significant economic losses. The main objective in this study was biological control of P. brassicae. Some isolated samples of rhizosphere soil and root, stem, leaf, shoot were collected from tea, virgin, ginkgo tree, and cabbage back to laboratory. Hundreds of strains were separated and antagonistic strains were filtered out by measuring the dormant spore germination rate of P. brassicae. Two strains of antagonistic bacteria were selected as the research material and the fermentation conditions of these two antagonistic bacterias were studied. The main types and amount of additives of the seed coating were screened out through a series of screening tests, and the seed coating formulations were determined. Coated treatments were respectively used on the cabbage and rape seeds. Control efficiency of these two bacterial strains were studied through pot and field experiments of the coated seeds. The main results were showed as follows:1. Isolation,screening and identification of antagonistic bacteriaA total of 702 strains were isolated from different soil and other materials in the experiment, including 345 strains of bacteria,218 strains of actinomycete,139 strains of fungi 15 antagonistic strains that had better inhibition on dormant spores of the P. brassicae were selected after screening. There were 7 strains of bacteria including X203, X6, X189, X144, X85, X15, X169 and 8 strains of actinomycetes including F118, F144, F187, F86, F13, F183, F36, F121. X203 was the best one whose inhibition rate of dormant spores of P.brassicae reached 68.42%, The inhibition effects of X189, F36 and F118 were also good. After initial identification we learned that these two antagonistic bacteria strains both were Bacillus spp.2. The fermentation conditions of two strains of bacteria of X203 and X189The effect of the amount of biomass produced of different fermentation conditions were studied. The fermentation conditions included media type, carbon, nitrogen, temperature, pH, the amount of the initial inoculation, shake bottle feeding amount and fermentation time on X203 and X189. The results showed that the best fermentation conditions of X203 were:medium was NYBD medium, carbon source was glucose, nitrogen source was yeast extract, the best temperature was 32℃, pH value was 6, the amount of initial access strains was 0.5%, shake bottle feeding amount was 20 mL/250 mL, fermentation time was 36 h. the best fermentation conditions of X189 were:medium was the YSP medium, carbon source was starch, nitrogen source was yeast extract, the best temperature was 28℃, pH value was 7, the initial inoculation amount was 5%, shake bottle feeding amount was 20 mL/250 mL, fermentation time was 48 h.3. Development of the biocontrol seed coatingThe seed coating formulations of the two strains of antagonistic bacteria were studied. The major types and amount of additives were identified through orthogonal experiments, the measurement standards of which were germination rates of rape seed and other physical and chemical properties of the seed coating. The major types of the additives were dextrin, opened powder and sodium carboxymethyl cellulose, and their dosage were 3%,1.5% and 1%. Through the characters detection tests of the seed coating confirmed that the two seed coating that the active substances of which is bacteria the indicators had reached the national standard.4. The experiment on the control of the biocontrol seed coatingThrough the control effect of pot experiments and field experiments of these two seed coating products, the results showed that, these two strains of antagonistic bacteria X203 and X189 both showed biocontrol effect on P. brassicae. The control efficiency of the coating treatment of X203 on the cabbage was the highest, the control efficiency of pot experiment was 62.62%, and the control efficiency of field test achieved 61.52%. The control efficiency of the coating treatment of X189 was slightly lower than X203. But the pop control effect of the two coating treatment of antagonistic strains on varieties of Chinese cabbage and rape were between 56.52% and 62.62%, while the field control effect were between 58.25% and 61.52%. After experiment of control efficiency we knew that the effect of the two coating treatment of antagonistic strains were significantly higher than the treatment of using the culture fluid of antagonistic bacteria watering the roots. And the effect of using the carbendazim watering the roots were between the coating treatment and treatment of using the culture fluid of antagonistic bacteria watering the roots.