ROOT AND SHOOT GROWTH UNDER FLOODED SOIL IN WILD GROUNDNUT (Glycine soja) AS A GENETIC RESOURCE OF WATERLOGGING TOLERANCE FOR SOYBEAN (Glycine max)

Water logging injury is a significant problem in soybean (G. max Merr.) production in Japan, because it is cultivated mostly in the converted paddy field. Wild groundnut (G. soja Sieb. et Zucc.), an ancestor of soybean, is growing around paddy field as a weed throughout the country. In order to evaluate waterlogging injury tolerance as a genetic resource for soybean, root and shoot growth in wild groundnut were investigated under the treatments by raised groundwater level upto soil surface for 21 days at the primary leaf and the flowering stages compared with soybean (cv. Ryuho). At the end of treatment of primary leaf stage, root length density (RLD) increased to 320%, and shoot dry matter weight per plant (DMW) decreased to 31% against no-treatment in wild groundnut, while influences on RLD and DMW were inconspicuous in soybean. It was considered that wild groundnut responded to excess water stress by increasing lateral root with root formation. At the end of treatment of flowering stage, RLD and DMW were not influenced in either species. However, the number of root nodules decreased greater in wild groundnut than in soybean, suggesting the difference in susceptibility to waterlogging injury at the flowering stage between these species. Reduction in leaf chlorophyll content by the treatment was observed continuously until maturity stage only in wild groundnut. At the maturing stage, grain yield in wild groundnut and pod number in soybean were measured to determine recovery from damages by the treatments. In wild groundnut, grain yield was equal to no treatment as well as pod number of soybean, and decreased to 15% by the treatments at the primary leaf and the flowering stages, respectively. However in soybean, pod number decreased to 54% by treatment at the flowering stage. Considering the severe damage in DMW at the end of treatment of primary leaf stage, wild groundnut showed higher ability to recover from the damage by the treatment than soybean. Consequently, it was suggested that waterlogging tolerance in wild groundnut might be related to the amount and the activity of root. Importance of root aerenchyma for waterlogging tolerance in soybean have been reported by many researchers. Therefore root development including aerenchyma formation under flooded condition should be investigated to utilize wild groundnut as a genetic resource of waterlogging tolerance for soybean.