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Summary
The most marked and nutritionally valuable effect of the opaque-2 and floury-2 mutants is that the concentrations of the essential amino acids lysine and tryptophan are considerably increased in the endosperm proteins of the maize. In addition, an increased methionine content is associated with the floury-2 mutant. While this finding is of great potential benefit in the nutrition of human beings and monogastric animals, the action of these mutant genes is also associated with less desirable agronomic characteristics such as lower yields, a poorer grain quality and, in the case of the opaque-2 mutant, a lower protein percentage. The data presented highlight some of the breeding problems encountered in the recovery of existing élite breeding material in a programme of conversion to the mutant genes (the emphasis being on the opaque-2 gene). Final analysis suggests that sufficient genetic variation exists in respect of most of the important agronomic and nutritional factors associated with high-lysine maize to attain its full potential by selection and breeding.