Effects of Flooding-induced Changes in Bradyrhizobia Occupancy on the Growth of Adzuki Bean (Vigna angularis)

We herein exami-ned the effects of soil flooding treatments on the occupancy of adzuki bean-nodulated bradyrhizobia and how changes in its occupancy affects adzuki bean growth. Microcosms containing mixtures of four different strains were prepared and incubated under flooded and non-flooded conditions. These microcosms were then used to cultivate adzuki bean in culture pots. After assessing the growth parameters of the plants, nodules collected from the roots were analyzed to assess occupancy rates. Be31, which exhibited a similar restriction fragment length polymorphism (RFLP) pattern in the 16S-23S rRNA gene ITS region to Bradyrhizobium elkanii USDA 31, was dominant overall. However, its occupancy declined under flooded conditions, while the occupancy of Bd110, similar to Bradyrhizobium diazoefficiens USDA 110^T, increased. Furthermore, a non-metric multidimensional scaling anal-ysis showed that adzuki bean-nodulated bradyrhizobial communities were affected by changes in Bd110 and Be31 occupancies due to soil flooding. In terms of growth, shoot length and shoot dry weight generally increased in cultivars where Bd110 occupancy surpassed that of Be31 under flooding. A correlation anal-ysis revealed that Bd110 occupancy correlated with shoot dry weight. These results suggest that increased Bd110 occupancy through soil flooding enhanced adzuki bean growth. However, alternative methods need to be considered in order to more effectively regulate Be31 occupancy.