Grain discoloration (GD) of rice (Oryza sativa) is a disease complex that occurs on rice panicles as a result of infection by various fungi. Bacillus megaterium, a bacterial antagonist that is effective against sheath blight of rice, was cultured using either nutrient broth, potato dextrose broth or a common household flavour enhancer. Preliminary data from a single experiment suggested that all three cultures supported growth of the bacterium. Spraying diluted bacterial nutrient-broth culture onto rice (var. RD 31) three times (41, 84 and 96 days after transplanting) reduced the mean severity of GD as a result of the field trials from three consecutive growing seasons. The spray did not affect the percentage germination of the rice seeds after they had been stored for three months in the laboratory at room temperature (26ºC—32ºC).
Bacillus megaterium is a beneficial bacterium that is used as a biological control agent (BCA) against the fungi Rhizoctonia solani, Fusarium sacchari and Curvularia lunata, which attack rice plants. However, the cost of preparing the bacterium using standard nutrient broth is prohibitively expensive on a large scale. Therefore, a low-cost product (seasoning cube, a common ingredient for cooking) was examined as an alternative nutrient medium. Bacillus megaterium was cultured in either nutrient broth or in dissolved seasoning cube. These cultures were evaluated for their effect on the growth of rice seedlings in the laboratory and to suppress grain discoloration of rice in small-scale field trials. Bacillus megaterium cultured with a seasoning cube was as effective as standard nutrient broth for the growth of rice seedlings in the laboratory. It also suppressed grain discoloration disease of rice in small-scale field trials. Use of a seasoning cube is suitable for culturing B. megaterium and should be recommended to farmers.
Indole-3-acetic acid (IAA) is one of the most physiologically active auxins produced by rhizobacteria and is potentially applied for agriculture. Two endophytic bacteria, VR2 and MG9, isolated from the root of Chrysopogon zizanioides (L.) collected at Cha-Am, and the leaf of Bruguiera cylindrica (L.) Blume collected from a mangrove forest at Ban Laem, Phetchaburi Province, Thailand, were taxonomic characterised based on their phenotypic characteristics and 16S rRNA gene analysis. Strain VR2 was closely related to Enterobacter hormaechei CIP 103441T (99.6% similarity), while strain MG9 was closely related to Bacillus aryabhattai B8W22T (99.9% similarity). Consequently, they were identified as Enterobacter hormaechei and Bacillus aryabhattai, respectively. The IAA production of VR2 and MG9 strains are determined and applied to rice seeds for their root and shoot germination. Strains VR2 and MG9 greatly produced a yield of IAA, 246.00 and 195.55 µg/mL in 1,000 µg/mL of L-tryptophan at pH 6 for 48 h. They showed no significant differences in IAA to root and shoot development. However, the bacterial IAA exhibited potential nearby synthetic IAA, which had a significant effect compared to the control. IAA produced from these two strains might preferably trim down the use of synthetic IAA and could contribute to sustainable agriculture.
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