Evaluation Of Endophytic Actinomyce OsiRt-1 For Biocontrol Of Rice Blast Disease

Rice blast disease is one of the biggest threat diseases on rice production, caused by wide-spread pathogenic fungi Magnaporthe oryzae. However, perpetual use of chemical agents have the negative impacts on the balance of environment and human health. The high degree of pathogenic variability of M. oryzae can rapidly overcome plant resistance, thus remains a continuous threat to the effectiveness of blast-resistant rice varieties. Hence, a growing number of scientists have increased interest in searching for microbial resources to control plant disease since they are generally recognized to be more environmentally friendly, having low toxicity. Endophyte is a significantly important part of microbial ecosystem in plants, which can survive in the inner parts of plants, meanwhile, exert beneficial effects on plants. In recent years, the endophytes have been proven to be a potential source for biocontrol agents. OsiRt-1, isolated from Gumei 4 rice samples when they were 11-week-old in our lab, exhibited remarkable antagonistic activity. In order to further evaluate the disease control effect of OsiRt-1 and to preliminarily study its potential antagonistic mechanism, the research content in this paper mainly includes following four parts:1. Based on morphological, physiological and biochemical characteristics and 16S rRNA gene sequence analysis, OsiRt-1 was identified as Streptomyces misionensis OsiRt-1.2. We tested the in vitro antagonistic activity of OsiRt-1.Using dual culture assay, we observed a remarkable antagonistic activity against 5 major physiological races of M.oryzae RB3, Guy11,61,62 and SO7,and obvious antagonistic activity against 2 major physiological races of M.oryzae RB3, Guy11 with the inhibition zone not less than 20 mm. We observed the effect of the antagonist on the hyphae of pathogen under Scanning Electron Microscopy. The pathogen Magnaporthe oryzae treated by OsiRt-1 revealed significant morphological alterations in hyphe including cell shrinkage, cell expansion. We tested the in vitro antagonistic activity of fermentation broth by growth rate method.The inhibition rate became bigger with the OsiRt-1 culture time extending, and the six day's culture filtrates exerted the strongest effect of antagonistic activity with a percent of 28.06%.3. We confirmed that OsiRt-1 has the ability to secrete several enzymes such as cellulase, protease and can produce siderophore, IAA and ACC deaminase. We checked that OsiRt-1 is positive for PKSII and NRPS genes.4. Biocontrol efficacy of OsiRt-1 against rice blast in field condition was evaluated. In field condition, we evaluated the disease index of seedling blast after spraying the antagonist spore solution on rice at 10 and 20 d. OsiRt-1 spore solution could reduce seedling blast severity by 7.76%, we evaluated the disease index of panicle blast and lose rate at 110 d after spraying the antagonist spore solution on rice at 10,20,50 and 80 d. OsiRt-1 spore solution could reduce panicle blast disease severity by 25.65% and lose rate by 17.46%. The separation rate of OsiRt-1 from above-ground portion of rice treated with OsiRt-1 is higher than the not treated ones. In summary, these data show endophytic Streptomyces misionensis OsiRt-1 has the application potential in agricultureas a biocontrol agent against rice blast disease.