Since 1964 when Mertz, Bates and Nelson (3) reported that the opaque-2 gene almost doubled the lysine content over normal corn, many breeders have introduced opaque-2 into normal endosperm genotypes. The first opaque-2 hybrids resulting from these conversions were not overwhelmingly accepted by farmers due to undesirable soft-floury kernel characteristics and relatively low yields in comparison to their normal counterparts. To overcome the deficiencies of opaque-2 types breeders have focused their attention on selection for higher test weight and modified endosperm. The resulting modified endosperm types have more vitreous fractions that may range from slight mottling, through half-and-half mottling, to nearly fully normal. Not all modified opaque-2 endosperm types are as high in lysine as the full opaque, but modified types with nearly normal endosperm have been identified with lysine values nearly equal to the opaque-2 phenotype. Our experience suggests that modified types should be monitored for lysine content during the selection process. The main objective of this paper is not to cover in depth the economic virtues of high-lysine corn. However, it should be emphasized that whether or not farmers accept high-lysine corn will depend largely on whether it is more profitable than the corn they are now growing. Many factors will enter into the decision-making process, including yield, susceptibility to kernel rots and insects, and the price of protein supplements. During the past ten years, one of the main concerns of corn breeders has been to improve the kernel characteristics of opaque-2. New hybrids are now emerging from breeding programs that have, in part, overcome some of the deficiencies of opaque-2. Double recessives, such as the su2 gene, in combination with opaque-2 have been tried. Some of these combinations have hard, vitreous endosperms that are high-lysine but are also low in yield. Another possibility which we have been exploring is increasing lysine by cyclic selection in normal corn in the absence of endosperm mutants. This paper will report on the results we have thus far obtained from this approach. Surveys by investigators Aquirre et al. (1), Tello et al. (5), and
Paez et al. (4) indicated a considerable range in lysine content among different races and strains of maize. Their results suggest that cyclic procedures can be used to increase lysine in normal endosperm maize, providing the genetic and environmental effects could be separated.

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