Harnessing Streptomyces spp. as rice plant growth promoter and biocontrol agent against Bacterial Panicle Blig

Bacterial panicle blight (BPB) disease caused by Burkholderia glumae is an alarming disease of rice. Controlling BPB using chemical control and BPBresistant rice cultivars is expensive and inconsistent due to chemical resistance strains’ development. Using plant growth-promoting bacteria to enhance rice plant growth and suppress pathogens is considered safe, environmentally friendly, long-lasting and inexpensive. This study aimed to investigate the roles of Streptomyces spp. as rice plant growth promoter and biocontrol agent against B. glumae. A total of 50 Streptomyces isolates were obtained from rice fields, and 22% showed antagonistic activity against B. glumae. The best three plant growth-promoting Streptomyces (PGPS) isolates, S. corchorusii TBR11, S. corchorusii JAS2 and S. misionensis TBS5 with plant growth-promoting (PGP) abilities and biocontrol activity against B. glumae were identified and characterised. The identity of PGPS isolates was confirmed based on 16S rRNA and phylogenetic tree analyses and multilocus sequence analysis (MLSA) by amplifying gyrB, rpoB and trpB using the polymerase chain reaction (PCR). Through API® ZYM analysis, the PGPS isolates showed enzymatic activities crucial in plant growth promotion. The PGPS isolates showed the highest (80%) PGP traits, including fixing nitrogen, solubilising phosphate and producing siderophore and indole-3-acetic acid. For antagonistic activity, TBS5 (26.35 ± 0.14 mm) exhibited the most antagonistic activity against B. glumae (p ≤ 0.05). The supernatant of PGPS isolates reduced the survival viability of B. glumae more than 50.7%. Scanning electron microscopy (SEM) indicated that substantial morphological changes occurred in the cell membranes of B. glumae after the PGPS treatment. Rice seeds treated with PGPS isolates improved vigour index by more than 100% compared to the control plants. Under the greenhouse study, TBR11 (149%) and TBS5 (141%)-treated plants showed a higher rice yield than the control (100%). The BPB disease severity was reduced by up to 27% and 39% for TBR11 and TBS5-treated plants, respectively. The talc-kaolin-Streptomyces bioformulations (BioSTBR11, BioSJAS2 and BioSTBS5 containing TBR11, JAS2 and TBS5, respectively) were successfully prepared and showed no phytotoxic effect on rice plants. Bioformulations were more stable when stored under refrigeration than at room temperature, with more than 50% spore viability at 180 days after storage. Treatment with BioSTBR11 and BioSTBS5 reduced BPB disease severity by up to 7% and 10%, and increased rice yield by up to 301% and 170% relative to control (100%), respectively. Transcript levels of defense-related genes (Gns1, OsPR1a, Oswrky45 and OsJAMYB) were up-regulated by the treatment with BioSTBR11 and BioSTBS5 at 7 days after infection than the control. Results suggest that the PGPS isolates, especially S. corchorusii TBR11 and S. misionensis TBS5 are promising candidates for enhancing rice yield and suppressing BPB disease. Overall, this study offers biocontrol solution for suppressing BPB disease by utilising PGPS, which can be incorporated as one of the BPB disease management strategies.

Text 124781.pdf Download (1MB) Official URL or Download Paper: http://ethesis.upm.edu.my/id/eprint/18781

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