Methionine Concentration in Soybean Protein from Populations selected for Increased Percent Protein 1

When a component of grain, such as protein or oil, is changed quantitatively through plant breeding, it is important that the quality of that component be maintained. The current study was conducted to determine if protein quality, as measured by methionine concentration, had changed as a result of recurrent selection for increased protein in four soybean [ Glycine max (L.) Merr.] populations. Selected cycles from four populations were grown in replicated field experiments in 1975 and 1976. Two populations, designated IA and IB, were grown in one environment; the other two, designated IIA and IIB, were grown in another environment. In 1978, populations IA and IIA were tested together in a replicated field experiment in two environments. Percent protein of the seed and methionine concentration of the protein were determined in all experiments. Differences in methionine concentration among selected cycles of the four populations tested in 1975 and 1976 were generally small. Therefore, selection for high percent protein in the soybean populations did not result in large changes in methionine levels in the protein. Population IA protein had a lower mean concentration of methionine than population IIA. When populations IA and IIA were tested together in two environments in 1978, differences in methionine percentage of the protein among cycles of selection were nonsignificant, as before. However, the average methionine concentration of the two were similar and location by cycle interactions were highly significant. These results suggest that the differences in methionine concentration, previously observed between populations I and II, were a result of environmental influences. The lack of relationship between protein percent and methionine concentration of protein demonstrates that methionine is not likely to decrease as a result of selection for higher protein, at least not in early cycles of selection