Identification of an endophytic actinomyce OsiRt-1 isolated from rice and its effect against rice blast disease

Abstract:

[Objective] To isolate, screen and identify rice endophytic actinomyces with antagonistic activity against rice blast pathogen, to evaluate the disease control effect of the selected antagonist and to study its potential antagonistic mechanism. [Methods] We used 4 isolation media to isolate endophytic actinomycetes from surface sterilized rice. Using dual culture assay, we screened the strain with antagonistic activity and identified it by morphological, physiological and biochemical characteristics and 16S rRNA gene sequence analysis. We observed the effect of the antagonist on the hyphae of pathogen under scanning electron microscopy and tested the in vitro antagonistic activity of fermentation broth by growth rate method. In field condition, we evaluated the disease control efficiency after spraying the antagonist spore solution on rice. Meanwhile, we analyzed enzymes and secondary metabolites production of the antagonist, and amplified its polyketide synthases (PKSⅡ) and nonribosomal peptide synthetases (NRPS) genes. [Results] From 1 800 rice samples, a total of 117 endophytic actinomycetes were isolated, among which, OsiRt-1 exhibited remarkable antagonistic activity. OsiRt-1 was identified as Streptomyces misionensis. The pathogen Magnaporthe oryzae treated by OsiRt-1 revealed significant morphological alterations in hyphe and its mycelial growth was inhibited by culture filtrates of OsiRt-1 with a percent of 28.06%. In field condition, OsiRt-1 spore solution could reduce seedling blast severity by 7.76%, 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. Besides, OsiRt-1 is positive for PKSⅡ and NRPS genes and can produce cellulase, protease, siderophore, IAA and ACC deaminase. [Conclusion] Endophytic Streptomyces misionensis OsiRt-1 has the application potential in agriculture as a biocontrol agent against rice blast disease.