Current status of quality improvement in maize

A review on quality improvement of maize (Zea mays L.) was made to summarize the accomplishements of the past and the perspectives in the future. Various endosperm mutants affecting carbohydrate, starch and protein of maize kernels and brown midrib mutant genes affecting nutritional quality of corn plants as well as selection methods effectively used to increase protein and oil contents in maize kernels were the major contents of this study. Endosperm mutants of maize were extensively investigated to understand the basic biochemical procedures on carbohydrate and starch synthesis as well as to improve starch and sweet corn quality. A group of mutants (bt, bt2, sh, sh2 and sh4) are deficient in enzymes necessay for the conversion of sucrose to the substrate for the starch synthesis, while another group of mutants (ae, du, su and wx) possibly results from loesions in the enzymatic reactions forming starch. Single, double, or triple mutants are successively utilized to produce sweet corn varieties with better quality. Amylose or amylopectin contents of corn starch could be modified rather easily with appropriate combination of ae, du, su, suz, and wx genes. However, the modification is restricted by the social or industrial demand rather than genetic or technical requirement. Quantitative increase and qualitative improvement of protein in maize kernels have been studies more extensively than any other cereal crops. Selection experiment to select maize with higher protein was estabilished in 1986 at the Illinois Agriucltural Experiment Station and proved to be successful over 76 generations in selecting for both increased and decreased protein content. However, this work did not produce the anticipated commercially applicable results. The discovery of the effects of the opaque-2 and floury-2 genes on the modificaion of protein in maize kernels initiated extensive studies on nutritional qualtity of other cereals as well as of maize. The increased contents of lysine and tryptophan associated with these genes greatly enhanced nutritional value of maize for both human diet and animal feed