Efficacy of antagonistic bacteria for controlling fungal rice (Oryza sativa L.) pathogens.

A total of 59 bacterial isolates were isolated from the rhizosphere soil of rice in Tha-rang sub-district, Ban-Lham district, Phetchaburi province. The preliminary study was conducted using a dual culture assay to investigate the efficacy of antagonistic bacteria to control rice fungal diseases, which include Curvularia spp., Fusarium spp. and Rhizoctonia spp. The result showed that 5 isolates: BL-44, BL-48, BL-55, BL-56 and BL-59 have an efficiency to control the fungal pathogens. The BL-59 isolate revealed a maximal percentage of mycelial growth inhibition against Curvularia spp. (65.67%) and Fusarium spp. (54.74%) and BL-44 isolate showed a maximal mycelial growth inhibition percentage (PIRG) against Rhizoctonia spp. (74.29%) (P<0.05) using PDA medium. Whereas, the inhibitory activity of BL-59, which performed on TSA medium had highly PIRG values of 93.33, 82.84 and 31.03% against Curvularia spp., Fusarium spp. and Rhizoctonia spp. tested on TSA medium, respectively. The volatile assay revealed that BL-44 isolate showed the highest antifungal efficacy against Curvularia spp. (82.26%) and Fusarium spp. (67.86%), whereas BL-48 and BL-56 isolates showed the highest antifungal efficacy against Rhizoctonia spp. by 73.33 and 76.67%, respectively (P<0.05). Microscopic observation of the hyphal morphology of fungal diseases revealed the severely damaged hyphae, including deformation, loss of apical growth, and lysis. Furthermore, these bacterial isolates produced volatile compounds that inhibited mycelial growth and reduced pigment production. In addition, BL-44 and BL-56 isolates demonstrated temperature endurance from 20 to 50ºC. BL-48 and BL-59 demonstrated tolerate salinity levels ranging from 4 to 7% NaCl. BL-48, BL-56 and BL-59 isolates were identified as Enterobacter roggenkampii, Enterobacter cloacae and Bacillus subtilis subsp. spizizenii based on 16S rRNA analysis. As a result, the antagonistic bacteria isolated from this study can be used as an alternative choice to control rice diseases caused by fungal pathogens.