The inheritance of leaf abscission and other characters in soybeans

The inheritance of 10 qualitative characters in soybeans was studied and reported on. A number of these characters have been studied previously and the mode of inheritance confirmed in the present work. A new hypothesis for the explanation of pubescence color has been presented. Several characters were reported on for the first time in this work; these include leaf abscission, pseudo-mosaic plant type, and three chlorophyll-deficient types. Normal leaf abscission was found to differ from delayed leaf abscission by one gene. The symbols Ab, ab were assigned to this allelomorphic pair. This character was not found to be linked with any of the nine characters with which it was studied. A mosaic-like mutant designated as "pseudo-mosaic" was described and found to be inherited as a simple recessive to the normal type plant. The symbols Pm, pm were assigned to this allelomorphic pair. No linkage studies were made with this type. Three chlorophyll-deficient types, designated as y8, y9, and y10, were described and each found to be inherited as a simple recessive to the normal green type. The y9 type showed no linkage with the three characters with which it was tested. The other two types were not tested for linkage. Pubescence color was studied in a number of crosses from which some interesting and unusual ratios were obtained. These studies provided considerable evidence that several genes are responsible for pubescence color. In order to explain the results of present studies as well as results of previous investigators the hypothesis was advanced that duplicate genes T1 and T2 produce tawny pubescence; R2 is linked with T1 and T2 inhibits tawny pubescence in the presence of r2. On the basis of this hypothesis the genetic constitution of the true breeding gray types is r2T1 r2T1 T2T2, r2t1 r2t1 T2T2, r2t1 r2t1 t2t2, and R2t1 R2t1 t2t2 and the genetic constitution of the true breeding tawny types is R2T1 R2T1 T2T2, R2T1 R2T1t2t2, R2t1 R2t1 T2T2, and r2T1 r2T1 t2t2. The breeding behavior of these types in all possible combinations is presented through F3. Data from two crosses are presented on the inheritance of seedcoat colors, seedcoat patterns, hilum colors, and defective seedcoat, and their inheritance discussed in view of the hypothesis for the explanation of pubescence color. Green seedcoat is dominant to yellow seedcoat and inherited in a simple Mendelian fashion. Self-black seedcoat is dominant to self-imperfect black and self-buff, and self-imperfect black is dominant to buff. These gave a ratio of 12:3:1 of the respective colors. Black and brown hilum colors are inherited in a similar manner. Restriction of color to the hilum is dominant to self-color in a ratio of 3:1. These data are in agreement with the work of previous investigators but the genetic constitution is changed somewhat for seedcoat and hilum colors because of the application of the hypothesis for pubescence color and its effect on seedcoat and hilum color. Defective seedcoat was found to be completely linked with gray pubescence, but inhibited by i(i) in the crosses studied and expressed only in the presence of i in all cases except with black-seeded gray-pubescent types such as Kingwa. A ratio of 15 normal to 1 defective was obtained which is in accord with previous work. The genes responsible for the occurrence of black-seeded gray-pubescent types seem to affect the expression of defective seedcoat since these types do not have defective seedcoats. A satisfactory explanation to account for the production of black-seeded gray-pubescent types and also the failure to recover this type in expected numbers in F2 when it is used as one of the parents in crosses was not reached. Data presented on the inheritance of flower color, stem color, plant type, and leaf type are in agreement with the findings of previous investigators.