The Screening And Identification Of Antagonistic Bacterial Strain AbⅢ745-6 And The Preliminarily Study On Its Antagonistic Metabolites

This research aimed at isolating and screening of antagonistic bacteria with great ability to suppress above-ground-plant-disease-causing agents such as Pyricularia orazye, searching for new resources for plant disease biological control, studying and analyzing the inhibitory substances produced by them preliminarily.Eleven antagonistic bacterial strains showing inhibiting effect on Pyricularia oryzae and Gaeumannomyces graminis were screened out of 117 bacteria strains isolated from rhizosphere soil on the basis of their suppressiveness in the in-vitro bioassay. A result of over 50% suppression of Pyricularia oryzae was obtained by eight of those suppressive original strains with the treatment of their fermentation filtrate, which amounted to 72.83% of the total antagonistic ones. Among those eight strains, there were three strains(namely Abâ…¢745,Abâ…¢763 and Abâ…¢716) showing an inhibiting rate of over 50% against both indicator pathogens, Abâ…¢745 particularly. According to the result of the suppression assay, strain Abâ…¢745-6,the single-cell isolated offspring of Abâ…¢745,was selected as the idealest one. It could inhibit the mycelium growth of Pyricularia oryzae by 96.88% and was preliminarily identified as Pseudomonas Fluorescens. The determination of suppression spectrum by strain Abâ…¢745-6 showed that this bacterial strain possessed a wide inhibiting spectrum. It inhibited many pathogens with high antagonistic effect, with over 90% inhibition against Pyricularia oryzae, Fusarium oxysporum f.lycopersici(sacc).snyder et Hanse, Altermaria solani, Fusarium oxysporum(scho).f.sp.cucumbrum Owen and Gaeumannomyces graminis; over 60% against Botrytis cirerea, Alternaria alternata, Venturia nashicola and Bipolaris sorokiniana. Also, it showed certain suppression of other indicator pathogens involved in this assay.Tests were taken in this study to figure out the best way for application of strain Abâ…¢745-6. Practice showed that seed-treatment with bacterial fermentation filtrate was the most effective and convenient way, with an inhibiting rate of 75.36% and a decrease of 22.54 in disease index against rice blast disease. Disease-controlling effect was fair with soil-treatment but not so good with leaf-spraying treatment with which the inhibiting rate was only 45.68% and decrease in disease index 14.38.Preliminary study on growth-promoting effects of strain Abâ…¢745-6 were conducted, with tomato, rice, tobacco and cucumber plants as tested plants. The results indicated that the bacterial fermentation(108-9cfu/ml) had different or even contrary effects on plant growth as different concentration treatments. There was a tendency of growth-promoting effects when treated with low concentrations while grow-inhibiting effects when the concentration was high enough. As a whole, the growth-promoting effect was the best when treated with fermentation diluted by 1100 times and it performed better on tomato and rice seedlings with their root length and plant height. One could easily tell that strain Abâ…¢745-6 possesses both plant disease control and plant growth-promoting potential based on above bioassay results.Substances with strong inhibiting activity were extracted from the filtrate of strain Abâ…¢745-6. After further purified, a single compound predominant in the fraction showing the most desirable suppressive activity was selected for closer study. It was primarily named Phenaminomethylacetic based on chemical analysis and structural identification, which turned out to be a new kind of inhibitory substance ever found in Fluorescent Pseudomonas spp..