Isolation And Identification Of Biocontrol Actinomycetes Against Rice Blast And Optimization Of Liquid Fermentation Conditions

Rice is one of the main crops in China.The rice blast has seriously affected the production of rice.At present,there is no desirable strategies to control the rice blast,but the microbial biocontrol agents are favored by people because of their function and no-pollution characters.In this study,the microbes against rice blast-causing pathogen were screened and isolated from the rhizosphere of wild Rice from Dongxiang,Jiangxi Province.Response surface method was used to optimize the fermentation conditions with the bacterial circle against rice blast as the index,and the biocontrol effect was evaluated by using the plants’ indexes from the pot experiment.The results are as the follows:1.Screening and identification of antagonistic bacteria against the rice Blast.Fifty-six strains were isolated from the rhizosphere of wild rice from Dongxiang,Jiangxi Province.Of them one strain named as actinomycete TL-007 with high resistance to the pathogen of rice blast was identified as Streptomyces Nigalater by phylogenetic analysis.The result of physiological and biochemical tests showed that TL-007 could hydrolyze starch,decompose chitin,liquefy gelatin and produce indoleacetic acid and hydrogen peroxide with a maximum salt tolerance of 10 %.In the plate confrontation experiment,the inhibition rates to rice blast,soybean black spot,Chinese cabbage black rot,ginseng sickle,ginseng rust rot and soybean grey mold were 89.5 %,81.48 %,80.37 %,82.66 %,85.93 % and 76.37 %,respectively.2.Optimization of the liquid fermentation conditions for TL-007The bacteriostatic circle against rice blast fungus was used for the response value,and the best single factors were determined by single factor experiment,and then several factors affecting fermentation were evaluated by Plackett Burman experiment and three key factors were identified including corn flour concentration,peptone concentration and inoculation amount.After the steepest climbing test,the optimal values of the three factors were obtained by box Behnken design including inoculation amount 7.67 %,corn flour concentration 16.69 g/L and peptone concentration 1.87 g/L.3.Confirmation of the biocontrol effects of TL-007 by using pot cultureThe fermentation liquid of TL-007 could stimulate the germination of rice seed,and the germination rate,the germination potential,and the germination index of TL007-treated rice seeds were 99.33 %,97 %,and 73.05,respectively,and they were higher than that of the control groups.The results of pot experiment showed that the disease index of the TL-007 treatment was 39.67,while the control was 49.67 %.The seedling length,fresh weight,dry weight,root length,fresh weight and dry weight of rice treated by TL-007 were higher than that of the control group(CK),and the increased percentage were 30.98 %,66.67 %,181 %,55.41 %,250 % and 200 % respectively.The seedling length,fresh weight,dry weight,root length,fresh weight and dry weight of rice seedlings inoculated with TL-007 and rice blast-causing pathogen were higher than that of the rice inoculated only with the pathogen alone,and the increased percentage was 20.32 %,71.79 %,71.43 %,58.98 %,83.33 % and 150 %,respectively.The results suggested that actinomycete TL-007 could not only provide resistance against rice blast,but also promote the growth of rice,so it has a great potential in the application for a sustainable agriculture.