Evaluation, Monitoring And Utilization Of Rice Sheath Blight Of Antagonistic Bacteria

One thousand bacteria isolates were isolated from the bulk samples of rice seeds from direct row seeding, direct broadcast seeding, and transplanting paddy field. They were tested against Rhizoctonia solani, Fusarium monil~forme and Ustilagginoidea virens, the causal organism of sheath blight, bakanae and false smut of rice, respectively. One hundred and seven isolates were antagonistic to R. solani, which was 10.7% of the total. Twenty-five isolates were antagonistic to the both pathogens of R. solani and F. monil~/orme, which was 2.5% of the total. Twenty-one isolates showed antagonistic to R. solani and U. virens, which was 2.1% of the total. Rice seeds were treated by the chemical 402, not only reduced the total amount of bacteria but also killed large amount of antagonistic bacteria against R. solani, which reduced the fluorescent antagonistic bacteria from 5.20% to 1.04% of the total. Seventy-nine antagonistic bacteria against R. solani reserved for a year in the lab were screened for antagonists again and twenty-two were antagonistic against R. solani and F monil~forme. Sixteen isolates were selected for identification by bacteriological and Biolog test. The Biolog similarity of seven isolates was above 0.50. They belong to genus of Pseudomonas and Curtobacterium. Twenty-two antagonistic bacterial isolates with three concentrations (lO9cfulml -, 8 10 cfulml and 1 O7cfi.t/ml) were applied for rice seed bacterization against R. solaniv in the screening-house and greenhouse. Antagonistic bacterium S90 132 was not effect on rice seed 53 germination with three different concentrations; but T90249~ T190860 and T220957 were seriously effect on seeds germination in every concentration, antagonistic bacteria T300363 and T220992 were serious effect on germination in 1 O9cfu/ml, but were not effect in lO8cfuIml and l07cfulml; Antagonistic bacteria Y1908l and S300267 were seriously effect on germination in lO9cfu/ml and lO8cfuIml, but were not effect in lO7cfuIml. The results indicated that the sensitivity of seed germination against the concentrations greatly varied with the antagonistic strains. The different strains were different promotion or inhibition to the root and seedling. Effect of antagonistic bacteria on promoting or inhibiting of the growth of the roots or shoots of rice also varied with the strains. Antagonistic bacteria Y4028 and T260109 inhibited the growth of the seedling root. Antagonistic bacteria Y120124 and T300363 promoted the seedling shoots, while T220988 and T130357 inhibited the seedling shoots. The colonization of antagonistic bacterium T90249, Y220338 and T260109 on surface of rice plant was studied for the better control effect on sheath blight of rice in the greenhouse. The results showed that the population of T90249 and Y220338 could maintain at 10~1O2 cfulg and lO-l04cfu/g 14 days after a spraying on seedling and adult plants. However, T90249 could not be detected 14 days after a spraying on the seedlings and the adult plants. The experiments also revealed that appropriated time to spray antagonistic bacteria was on the day or a day after inoculation of R. solani. The initial concentration of introduced antagonistic bacteria should not be lower than 108 cfu/ml which could have the better control effect. Three extracts from the antagonistic bacteria against R. solani were studied. Mycelia of R. solani were treated with the extracts for 24h. It found that the ten times dilution affected...