Genetic studies on the wild and cultivated soybeans

1. The fertility of the F1 plants and their progenies from the crosses of the wild and cultivated soybeans is as normal as that in the inter-varietal crosses. It indicates that a close phylogenetic relationship exists between these two species of plants. 2. Hybrid vigor was observed in the F1 hybrids, especially from the standpoint of number of branches and number of seeds per plants. 3. The mode of inheritance of such characters as stem color, flower color, pod color, seedcoat color, hilum color, pubescence color, pod bearing habit, bloom on seedcoat, and appressed pubescence are found to be the same as that of inter-varietal crosses made by previous investigators. 4. The sharp-tipped pubescence here reported as a new character is found to be dominant over the blunt-tipped one, and is controlled by a single pair of factors. 5. The hard seedcoat of the wild soybean is dominant to the soft seedcoat of the cultivated soybean in the F1 and a wide range of variation is observed in the F2. Since the soft-seeded F2 plants all bred true to the type in the F3, therefore, a single gene difference may be ascribed. 6. The height of plants as well as the size and shape of seeds are found to be quantitative in inheritance. The mean plant height and the shape index of seeds of the F1 hybrid plants all approached the smaller parent, while the frequency distribution of the above three characters are all found to be positively skew. 7. The yellow pod color (1) is linked with the determinated growth habit (dt), with a crossover value of 36.28%. The gene pairs 11 or dtdt are found to be independent of the first three linkage groups, while the relation between this gene pair and the fourth group on account of the lack of suitable tester has not yet been determined. 8. A crossover value of 37.91% has been obtained for the two linked characters gray pubescence and soft seedcoat. The soft seedcoat (h) is considered as a new gene to be added in the group 1, but its order in the chromosomal map has not been definitely placed. 9. Gray pubescence is found to be completely linked with both the grown hilum and defective seedcoat. 10. The genetic constitutions of the wild and cultivated soybeans are tentatively proposed as follows: A. Wild: WW TT B1B1 DtDt LL R1R1R2R2 GG ii B1B1B2B2B3B3 aa HH B. Cultivated: ww tt b1b1 dt dt 11 r1r1r2r2 gg ihih B1B1B2B2b3b3 AA hh 11. The mode of inheritance of various characters involved in this cross are summarized in Table 17.