Genetic structure of the Japanese soybean population

The genetic structure of the Japanese soybean population was evaluated base d on the variation at 16 isozyme and seed protein loci for 781 landraces an d pure line selections. A relatively high diversity was found in the Japane se population, compared with 158 Korean accessions and 94 Chinese accession s that were tested for comparison. The average gene diversity in the Japane se population was 0.248, being comparable to the estimate obtained for the Chinese population (0.249) but higher than that for the Korean population ( 0.209). There were a number of alleles that differentiated the Japanese pop ulation from either of the Korean or Chinese populations or both. The prese nce of the alleles which are characteristic of the Japanese population sugg ests that the Japanese population is not solely a part of the population of China, which is considered as the place of origin of soybean. Only 11% of the total variation was attributable to the differences among seven regiona l groups, which occurred mainly between Hokkaido or Okinawa and the other r egions. A test of two-locus associations revealed that the variation was it self highly structured despite the high level of variation at each of the p olymorphic loci. In addition, Aco1, Aco4, Dia1, Enp and Idh1 varied with ma turity or seed size. The Japanese soybean population may consist of differe nt cultivar groups that had been established independently as the result of adaptation to different environmental conditions and/or diversification of food culture. The origins of the cultivar groups are discussed.