| Rice blast, caused by the fungus Magnaporthe grisea, which has spread all over the world, severely affects rice production and quality. Developping biocontrol method to contol this disease is very significant for mankind and its society. This research was focused on Bacillus subtilis B-332 strain and its active antifungal compound to control rice blast disease, presented a systematic study on the inhibition to hyphae growth and spores germination in vitro, control efficacies of pot experiments and field trials. Forther more, the mechanism of action and the colonization of B-332 on rice leaves were also investigated. The results are as follows:(1) B. subtilis B-332 strain showed strong inhibitory activity against the hypha growth and spore germination of M. grisea in vitro. The average of inhibition zone was 23.69mm when they were dual cultured on PDA media. A series of diluted culture supernatant of B-332 strain from 5~800× had been tested and the results showed that the hypha can hardly grow at 5× and 10 ×;even 20 ×, and spore germination was completely suppressed. Although at 100—200 ×, most spores can germinate, more than 70% of germ tubes were malformed.(2) In pot plant experiments, B-332 strain and its culture supernatant showed significant control efficacies (over 50%) against rice blast, and the control efficacy of admixture of them was much better. The control efficacies were mainly contributed by preventing activity other than curative activity. The preventing efficacy is depending on the density of colonized B-332 strain on the rice leaves surface when inoculating the spores of M. grisea. The B-332 strain could colonize on rice leaves surface after introducing, and can be isolated 21 days later. The more population of B-332 strain could survive on the leaf with 10% infection lesions. In field trial, the control efficacy of rice panicle blast was 57.2%, increasing yield 9.6% when consistency of B-332 was at lxlO8 cfu/mL, and have no toxicity to crabs even at 5xl08 cfu/mL.(3) Microscopic observations suggest that B-332 can cause the germ-tube and mycelium of M. grisea formed bulgy sphere. When time passes, these malformed germ-tubes and hyphae become larger and larger, at last, the spherical deformations began to break and the cytoplasm oozed out of the cells, then the germ-tubes and hyphae collapsed. TEM (Transmission Electron Microscope) observations suggest that the ektexine of cell wall of M. grisea was dissolved by the culture supernatant of B-332 strain. At last, the deformed germ tube can not develop into normal appressorium which is necessary to penetrate the host cuticle for infection.(4) M. grisea were significantly inhibited by the crude solution of active extract of l.OOug/mL. The active extract are also excellent hot stable. The control efficacy of 5x condensed active extract solution was 72.63% in pot trial, and higher than that of tricyclazole.
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