| Rice blast is a fungal disease caused by Phyricularia grisea, which seriously influenced the yield of rice. Chemical pesticides and resistance breeding were the foremost methods to be usued to control rice blast, however the frequently occurring of new physiological races of pathogens and the environmental damage caused by chemical pesticides resulted in the urgent need for a sustainable and environmentally friendly method to control rice blast. Endophytes colonized in plant could compete with pathogens for living spaces and nutrients, such as carbon source, nitrogen source, phosphorus or iron carrier to inhibit the growth of pathogens, in addition, the antibiotics and other bioactive substances produced by endophytes could directly kill the pathogens, or by promoting plant growth indirectly improved the disease resistance of the host plant. In this study, an endophytic actinomycete strain OsiSh-10 significantly against rice blast pathogens was successful ly obtained from rice, and we analyzed the control effect on rice blast of OsiSh-10 after inoculating OsiSh-10 into rice, the effect on plant growth of metabolites produced by OsiSh-10. The aim of the article is to develop the theoretical foundation for the development of endophytes against rice blast in the future.The main contents and results are as follows:1. In this study, we isolated endophytic actinomyces from infected and uninfected Xiangaizao7 and Gumei4 rice samples respectively when they were 15, 80-day-old through optimized surface-sterilization combined with five kinds of isolation medium(WA, TWYE, MS, ISP4, HV). The isolation results showed that in the seedling period of 15 days, the endophytic actinomycete isolation frequency of infected Gumei4 rice samples was 0.158, significantly higher than that of uninfected Gumei4 rice samples(0.051). The endophytic actinomycete isolation frequency of infected Xiangaizao7 rice samples(0.097) was also higher than that of uninfected Xiangaizao7 rice samples(0.07). Howere, the isolation results of the 80-day-old were just opposite with that of the 15-day-old, the endophytic actinomycete isolation frequency of infected Gumei4 and infected Xiangaizao7 rice samples were lower than that of uninfected Gumei4 and uninfected Xiangaizao7 rice samples respectively. We screened antagonistic strains from actinomyces isolated from rice using a dual plate assay, and a strain OsiSh-10 significantly against rice blast pathogens was successfully obtained, according to its morphological features, culture characteristics, physiological biochemical characteristics, 16 S rDNA gene sequence comparison, and phylogenetic tree construction analysis, OsiSh-10 strain was classified as Streptomyces albus.2. For further studying the biocontrol potential of OsiSh-10 for rice blast pathogen, three distinct physiological races of rice blast pathogen were chosen, The dual plate assay results showed that the strain had strong antagonism to three target races.The biggest inhibition distance was 21 mm, the maximum inhibiting rate of mycelial growth was 59.1%, which indicated that OsiSh-10 strain had antagonistic effect significantly on Phyricularia grisea. The plate assay performed for detecting whether OsiSh-10 produced active substances related to antagonism produced. The results showed that OsiSh-10 strain can’t secrete cellulase, hemicellulase, chitinase and HCN, but is capable of producing iron carrier, and produces some diffusile antagonistic substances with big polarity growing on PDA medium. The control effects of OsiSh-10 on leaf blast in field was investigated. The results showed that disease index of leaf blast of rice sprayed once and twice with OsiSh-10 strain spores suspension was 37.7% and 31.01% respectively, both were lower than that of rice that coated seeds(55.73%) and untreated(46.75%) with OsiSh-10 strain spores suspension, these results revealed that leaf blast was controlled by spraying OsiSh-10 on leaf of rice, and the control efficiency of spraying twice better than that of once.3. Through vertically co-culturing OsiSh-10 with Arabidopsis thaliana, we discovered that the strain promoted the primary root elongation when OsiSh-10 was placed above Arabidopsis thaliana root, while it suppressed primary root elongation, and enhanced lateral root emergence when OsiSh-10 was placed below Arabidopsis thaliana root. The study of bioactive substances related to plant growth-promoting secreted by OsiSh-10 indicated that the strain couldn’t produce soluble phosphorus factor, but produce iron carrier, ACC deaminase, IAA. LC-MS analysis showed that OsiSh-10 also secreted kinetin(KT). The results suggested that OsiSh-10 strain could contribute to Arabidopsis thaliana root development via multiple pathways. |
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