| Rice blast, one of the most harmful rice diseases, is caused by Magnaporthe grisea which seriously damaged the yield of rice in recent decades. Currently, the main prevention and arrangement against rice blast still depends on the chemical pesticides and resistance breeding. However, environmental pollution caused by chemical pesticides and the emergence of new pathogenic physiological races, resulting in an urgent need to find green, sustainable means to control the rice blast. Endophytic actinomycetes do not need to compete with soil microorganism.They may resist the pathogen infection directly, or promote the growth of plants and induce an immune response to improve host plant disease resistance indirectly. So it has attracted much attention as a new biocontrol resource. In this study, an endophytic actinomycete strain OsiLf-2 significantly against rice blast pathogens was successfully obtained from rice leaves. Tthe antagonistic properties, culture conditions and the active material were explored for further understanding of resistant mechanism and agricultural exploitation potential of OsiLf-2. The main contents and results are as follows: 1. Four isolation medias were used to isolate endophytic actinomycetes from surface-sterilized rice leaves with different sizes of lesions, and dual culture assay was carried out to screen antagonistic isolates. OsiLf-2 was found with obvious antagonistic activity against different physiological races of Magnaporthe grisea. with the highest inhibitory rate up to 83.0% against Guyl 1. According to the morphological, cultural, physiological and biochemical characteristics and the 16S rRNA sequence analysis, OsiLf-2 was identified as Streptomyces hydrogenans.2. Scanning electron microscope was used to observe the impact of OsiLf-2 on the mycelia form of M.grisea. The results showed that mycelia of M.grisea RB3 present obvious deformities and distortions after treated with OsiLf-2. Further investigation of the growth status of OsiLf-2 and the antagonistic activity of fermentation broth under different culture conditions, we found that OsiLf-2 can well grown in a variety of media, especially in rich medium such as ISP2 and PDB, the antagonistic activity of fermentation broth using ISP2 and PDB were also obvious with the inhibition rate up to 63.3% and 68.4% against M.grisea RB3 respectively. The culture initial pH 7, temperature 35? is most favorable for the growth of OsiLf-2, and the antagonistic activity of fermentation broth was also the strongest. In addition, fermentation broth of OsiLf-2 also showed good stability. It remained intact activity after treated with proteinase K, low temperature, strong light and UV for one hour; also maintained good antifungal activity after treated with strong acid and strong base for one hour; even still retained most of the activity after treatment at 100? for one hour.3. And OsiLf-2 was analyzed for secretion of antifungal related substances and compounds such like protease and siderophores were detected. After extracted with different polar extraction agents from mycelium and culture of OsiLf-2, ethyl acetate and petroleum ether extract were found with obvious antifungal activity and petroleum ether extract showed strongest antagonism. Growth-promoting related substance produced by OsiLf-2 were also detected, and OsiLf-2 could synthesize siderophore? IAA and ACC deaminase enzymes. When the 7-day-old PDA culture of the OsiLf-2 were applied on rice, the shoot and root length?shoot and root dry weight and chlorophyll content of rice seedlings were increased by 10%?34%?48%?10% and 16% compared with the control.In summary, endophytic actinomycete OsiLf-2 has good inhibitory effect on M.grisea and may promote the growth of rice seedlings. It was isolated from the interior of rice and would not cause secondary pollution to the surrounding environment and rice. OsiLf-2 showed considerable application potential in the biocontrol of rice blast and may be developed to new pesticides. |
PDF Full Text Request