Cyanobacterial Extract Mitigates Sheath Blight-Induced Damage in Rice: Biochemical and Molecular Responses to the Extract

Rice sheath blight (RSB) poses a serious threat to rice production, highlighting the importance of developing efficient and environmentally friendly biocontrol agents. In this study, we evaluated the ability of the cyanobacterium Constrictifilum sp. SCAU-26 to mitigate RSB damage in rice and investigated the corresponding rice responses. The results showed that cyanobacterial cell extracts were more effective than culture filtrate in inducing resistance against Rhizoctonia solani, and extracts from 20-day-old cultures exhibited greater efficacy than those from 12-day-old cultures. Non-targeted metabolomic analysis revealed that the relative concentrations of most metabolites in both cyanobacterial cells and culture medium were significantly higher at day 20 than at day 12, with substantial increases in potential resistance-inducing compounds. Pot experiments demonstrated that rice plants (Oryza sativa L. cv. Huanghuazhan) pretreated with cyanobacterial extract prior to R. solani inoculation (CYRS) exhibited significantly greater root dry weight and markedly lower lesion height rates compared with pathogen-only inoculated plants (RS), achieving a control efficacy of 52.6%. The CYRS treatment maintained high activities of polyphenol oxidase and β-1,3-glucanase. Transcriptomic analysis revealed significant alterations in the gene expression profiles of CYRS-treated plants compared with RS-treated plants, with 5287 differentially expressed genes. Integrated analysis suggested that, under cyanobacterial extract treatment, rice may reduce RSB damage by strengthening physical barriers, protecting the protein translation system, modulating hormone and metabolic flux, and enhancing targeted antimicrobial capacity.