This study demonstrates that root-associated Kosakonia oryziphila NP19, isolated from rice roots, is a promising plant growth-promoting bioagent and biopesticide for combating rice blast caused by Pyricularia oryzae. In vitro experiments were conducted on fresh leaves of Khao Dawk Mali 105 (KDML105) jasmine rice seedlings. The results showed that NP19 effectively inhibited the germination of P. oryzae fungal conidia. Fungal infection was suppressed across three different treatment conditions: rice colonized with NP19 and inoculated by fungal conidia, a mix of NP19 and fungal conidia concurrently inoculated on the leaves, and fungal conidia inoculation first followed by NP19 inoculation after 30 h. Additionally, NP19 reduced fungal mycelial growth by 9.9-53.4%. In pot experiments, NP19 enhanced the activities of peroxidase (POD) and superoxide dismutase (SOD) by 6.1-63.0% and 3.0-67.7%, respectively, indicating a boost in the plant's defense mechanisms. Compared to the uncolonized control, the NP19-colonized rice had 0.3-24.7% more pigment contents, 4.1% more filled grains per panicle, 26.3% greater filled grain yield, 34.4% higher harvest index, and 10.1% more content of the aroma compound 2-acetyl-1-pyrroline (2AP); for rice colonized with NP19 and infected with P. oryzae, these increases were 0.2-49.2%, 4.6%, 9.1%, 54.4%, and 7.5%, respectively. In field experiments, blast-infected rice that was colonized and/or inoculated with NP19 treatments had 15.1-27.2% more filled grains per panicle, 103.6-119.8% greater filled grain yield, and 18.0-35.8% higher 2AP content. A higher SOD activity (6.9-29.5%) was also observed in the above-mentioned rice than in the blast-infected rice that was not colonized and inoculated with NP19. Following blast infection, NP19 applied to leaves decreased blast lesion progression. Therefore, K. oryziphila NP19 was demonstrated to be a potential candidate for use as a plant growth-promoting bioagent and biopesticide for suppressing rice blast. Keywords Biocontrol agent, KDML105 jasmine rice, Kosakonia oryziphila, Plant growth-promoting bacteria, Rice blast fungi Abbreviations DMP 2,4-Dimethyl pyridine 2AP 2-Acetyl-1-pyrroline CAT Catalase CFU Colony forming units DAT Days after transplanting EC Electrical conductivity IAA Indole acetic acid NP19 Kosakonia oryziphila NP19
