1Tokyo University of Agriculture and Technology
Rice is the most widely consumed as staple food for the world’s human population, especially in Asia. South Vietnam is one of the largest rice production areas and rice export has contributed to Vietnamese economics. The rice plants represent a habitat for diverse microorganisms, which colonize the aerial parts (phyllosphere) and the root spaces (rhizosphere). Methylobacterium species are found frequently to inhabit in phyllosphere of plant and able to utilize the methanol emitted from plant tissues as carbon and energy sources. Several Methylobacterium species are known to have positive effects on plant growth. The aims of this study are (1) to understand genetic diversity of Methylobacterium associated with rice in Vietnam, (2) to characterize Methylobacterium isolates by stress tolerance tests and molecular analysis of several genes and (3) to screen the isolates with high plant-growth-promoting ability, particularly for rice.
Pink-pigmented methanol-utilizing bacteria, which are unique to Methylobacterium, were isolated from rice plants collected in 6 regions of South Vietnam. Based on 16S rRNA gene sequences, we found that Methylobacterium were predominantly located on the leaves and seeds. Phylogenetic analysis identified these 90 Methylobacterium isolates as M. radiotolerans, M. komagatae, M. platani, M. rhodium and M. salsuginis.
These isolates were tested for stress tolerance such as NaCl stress, low and high pH stress and low and high temperature. The presence of several genes related to plant growth promotion and methylotroph was analyzed by PCR-based method.
To examine the plant-growth-promoting ability, Methylobacterium isolates were inoculated to lettuce and rice. We found that several strains increased the length of leaves as well as plant weight. These results showed that Methylobacterium strains isolated in this study have a potential to become a biofertilizer for rice and other crops.