Yuichi Saeki

By Yuichi Saeki

Part of the book: Soybean

By Yuichi Saeki and Sokichi Shiro

Part of the book: Advances in Biology and Ecology of Nitrogen Fixation

By Maria Luisa Tabing Mason and Yuichi Saeki

The research about the indigenous soybean bradyrhizobia in the Philippines is scarce, and this greatly influences the improvement of soybean production in the country. Thus, soil samples were collected from 11 locations in the country and were used to isolate the indigenous bradyrhizobia in the soil. Through the use of polymerase chain reaction—restriction fragment length polymorphism (PCR-RFLP) and sequence analysis of the 16S rRNA gene, 16S-23S rRNA gene internal transcribed spacer (ITS) region and rpoB housekeeping gene, the most abundant and dominant indigenous bradyrhizobia in the country were identified. Then, the representative isolates of the most dominant species per location were used to test their symbiotic efficiency and N-fixation ability with the local soybean cultivars. The results showed that among all the tested indigenous strains, the B. elkanii IS-2 is the most effective and efficient microsymbiont of the Philippines’ local soybean cultivars. This report was able to provide necessary information on the distribution of soybean bradyrhizobia in the Philippines and characterized the symbiotic performance of the indigenous strains.

Part of the book: Nitrogen Fixation

By Sokichi Shiro and Yuichi Saeki

Some soybean varieties harbor the Rj genes, which regulate nodulation by preventing infection and nodulation by specific rhizobial strains. Soybean genotypes carrying several Rj genes may enhance the occupancy of useful bradyrhizobia, which exhibit potent nitrogen fixation ability and exhibit nodulation compatible with the Rj genotype of soybean. Therefore, we bred soybean lines presenting the Rj2Rj3Rj4 genotype by crossing the Japanese cultivars “Bonminori” (Rj2Rj3) and “Fukuyutaka” (Rj4) and studied the effects of Rj gene accumulation on productivity. To investigate yield components, three Rj gene-accumulated soybean lines (B × F − E, B × F − M, and B × F − L) and three soybean cultivars (“Enrei,” “Sachiyutaka,” and “Fukuyutaka”) were cultivated in 2016 and 2017. Pod and seed number and yield were the highest in B × F − M. The occupancy rate of isolates in cluster of Bradyrhizobium diazoefficiens USDA 110T carrying the hydrogen uptake genes tended to be lower in the Rj2Rj3Rj4 soybean lines than in “Sachiyutaka” and “Fukuyutaka.” Additionally, the occupancy rate of this cluster was positively correlated with yield. Therefore, promoting infection by bradyrhizobial strains carrying the hydrogen uptake genes may improve soybean productivity. Moreover, the Rj2Rj3Rj4 genotype of soybean may be inoculated with B. diazoefficiens USDA 110T, which is not restricted by the Rj2 gene, to further enhance soybean productivity.

Part of the book: Soybean