| 18 actinomyces and bacteria strains that have antagonistic activity against Alternaria alternata were isolated from tobacco, red pepper, tomato rhizospheric soil in Sangzhi , Liuyang , Changde. Actinomyces SZF2 and SZF7 have strongly antagonistic activity. In antibiotic test, the datum showed that antagonistic actinomyces extensive distribute in the plant rhizospheric soil, but the strongly antagonistic actinomyces were few. SZF2 and SZF7 , both isolated from the healthy tobacco soil in Sangzhi, were identified as Streptomyces spp.Optimum fermention condition for SZF2 and SZF7 were studied. According to the results, the best fermention condition as fellows:SZF2 optimum temperature is 30±1 ℃, SZF7 is 28±1 ℃. SZF2 pH value is 6.0, SZF7 is 7.0. Both of two antagonistic Streptomyces are grown well in the liquid medium 5 shaked for 96 hours, respectively. Meanwhile, the optimum foster way was shaked all day.Preliminary determined the potency of the fermentation filtrate of SZF2 and SZF7 against the pathogen was 600 times. The fermentation filtrate of SZF2 and SZF7 exhibited an inhibitory ability to 5 species of phytopathogenic fungi, this showed that the fermentation filtrate had a broad antibiotic spectrum. By the experiment of stability of an antifungal substances showed that continuous culturing up to 10 generations, SZF2 and SZF7 had a negative influences on inhibitory activity of their antifungal substances against the pathogen.Mechanism of control Alternaria alternata (Fries) Keissler with the fermentation filtrate of SZF2 and SZF7, microscopic observation showed that they could interfere the normal development of hyphae and conidiospores. The increased activities of POD, PPO in tobacco upon the treatment by fermentation extract of SZF2 and SZF7 were detected. This suggested the fermentation filtrate could trigger the defense reactions of tobacco plants. The germination of tobacco seeds was promoted by the fermentation filtrate and its diluent in the indoor environment test. |
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