A dual-function biocontrol agent, Kosakonia oryziphila NP19, suppresses rice blast and promotes rice growth by priming host defense responses

• At 2 DAI, OsALD1 expression significantly increased after rice blast was treated in non-bacterial colonized rice. • At 10 days after fungal inoculation (DAFI), rice blast resistance genes were up-regulated after fungal inoculation. • CAT, APOX, POX, and SOD activities increased after rice blast treated 2.2-100% in K. oryziphila NP19-colonized seedlings compared to non-bacterial colonized rice • As a result of priming defense responses, CAT, APOX, and POX activities increase in seedlings colonized with K. oryziphila NP19. • K. oryziphila NP19-colonization seedlings showed 16.5% disease reduction. Rice blast, caused by Pyricularia oryzae , is a devastating disease that threatens global food security. This study identifies the bacterium Kosakonia oryziphila NP19 as a multifaceted biocontrol agent and evaluates its ability to suppress disease, promote plant growth, and activate host defense mechanisms in rice. Colonization by K. oryziphila NP19 significantly reduced disease severity by 16.5%, reflected by a corresponding decrease in the area under the disease progression curve upon pathogen challenge. Additionally, treatment with the NP19 strain potently promoted plant growth, with increases shoot height of 12–17% and total biomass of up to 23% in fungus-inoculated seedlings compared with noncolonized controls. The protective effect was associated with priming the plant’s antioxidant system. In NP19-colonized seedlings, the activities of the antioxidant enzymes ascorbate peroxidase and peroxidase significantly increased although that of superoxide dismutase decreased under nonpathogenic conditions. In addition to physiological responses, NP19 altered the expression of defense-related genes in noncolonized seedlings in a temporal manner. The effects of NP19 are likely mediated by its ability to modulate the defense timeline, with OsALD1 upregulated early (2–10 days after fungal inoculation; DAFI) and pathogenesis-related genes ( OsPR1a, OsPR1b , and Cht-1 ) upregulated later (10–20 DAFI). Gas chromatography confirmed that NP19 produces diverse bioactive compounds, which likely contribute to disease suppression and growth promotion. Our findings identify K. oryziphila NP19 as a robust biocontrol candidate that confers resistance to rice blast by enhancing physiological defenses while promoting plant growth, suggesting that it is a promising tool for sustainable agriculture.