Biocontrol of blast disease in KDML105 rice by root-associated bacteria

Blast disease caused by the fungal pathogen Pyricularia oryzae is a serious disease affecting rice. The purpose of this study was to isolate, characterize, and identify chitinase-producing bacteria from the root-adhering soil and from the root surface and interior of two rice varieties, Khao Dawk Mali 105 (KDML105) and glutinous rice (RD6). In addition, their potential for promoting plant growth and inhibiting fungal pathogens was investigated in KDML105 rice seedlings. Among the 188 chitinase-producing bacteria screened, sixteen root-associated isolates showed plant growth-promoting traits and effectively inhibited P. oryzae in vitro. The plant growth-promoting activities included nitrogen fixation, phosphate solubilization, and indole acetic acid production. The effects of root-associated bacteria at 5 × 10⁹ CFU/isolate on the survival of rice plants challenged by spraying the leaves with a suspension of 10⁶ conidia of P. oryzae were investigated in vivo. Among the 16 tested isolates, colonization of KDML105 rice plants by the R-RD6-NP7 and R-RD6-NP19 isolates resulted in 86.67% to 83.33% and 98.33% to 96.67% survival of rice seedlings, respectively, at 7 to 45 days after fungal inoculation (DAI). In the pot–tray experiment, dead rice seedlings were first observed at 10 DAI, and at 30 DAI the survival of the R-RD6-NP7- and R-RD6-NP19-inoculated rice plants reached 97.67% and 99.33%, respectively. Spot inoculation of R-RD6-NP19 (identified as Kosakonia oryziphila) culture was performed on P. oryzae conidia on fresh rice leaves, and no symptoms of disease were observed. K. oryziphila NP19 is a root-associated and plant growth-promoting bacterium capable of colonizing rice plants and inhibiting rice blast fungal pathogens in the economical KDML105 rice variety. Therefore, this strain can be used as a bioinoculant to control rice blast disease in contaminated soils.