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The opaque‐2 mutation has been used in maize (Zea mays L.) breeding to develop cultivars with increased concentrations of lysine and tryptophan. Very little information is available, however, about combining ability for protein quality traits for modified/vitreous‐endosperm opaque‐2 maize (quality protein maize, or QPM), although such information is essential for planning an effective hybrid development program. This research assessed the relative importance of general and specific combining ability effects (GCA and SCA) for grain yield, protein concentration in grain, tryptophan concentration in grain, and tryptophan concentration in protein for various tropical, late maturity, white grained QPM lines. Four diallel trials, involving a total of 28 lines from five populations, were evaluated from 1988 to 1990, each at two to five locations during 1 yr. The best QPM hybrid in each trial exceeded the best normal‐endosperm maize check by an average of 14% for grain yield, 48% for tryptophan concentration in grain, and 60~ for tryptophan concentration in protein. Mean squares for GCA effects in across‐location analyses were significant (P < 0.05) for grain yield, protein concentration in grain, and tryptophan concentration in protein for three of the four trials, and for tryptophan concentration in grain in two trials. Mean squares for SCA effects were not significant except for grain yield in one diallel. Location × GCA interaction was generally significant for all traits except tryptophan concentration in protein. Our results suggest that QPM hybrids with the highest values for protein quality traits will be crosses between lines with the highest GCA values. Concurrent improvement of yield and protein quality should be possible for this germplasm because phenotypic correlation coefficients were not significant for grain yield with concentration of protein in grain, concentration of tryptophan in grain, and concentration of tryptophan in protein.

e.g., young children, pregnant or lactating women, and the ill, in countries where maize is a staple food and Quality protein maize (Zea mays L.) (QPM) can help alleviate often a significant source of protein.human malnutrition and reduce costs of animal feed because it contains the opaque-2 mutation, which results in increased lysine and tryp-QPM contains the opaque-2 mutation, which alters tophan concentrations and a higher biological value as a food than protein composition of the maize endosperm, resulting normal maize. To be commercially successful, however, QPM cultivars in increased concentrations of lysine and tryptophan must be agronomically competitive with normal-endosperm alterna- (Mertz et al., 1964). Because of the 60 to 100% increase tives while consistently achieving expected protein quality and endoin concentration of these two essential amino acids, insperm modification (i.e., translucent or near-normal phenotype) stancreased digestibility, and increased nitrogen uptake reladards. To assess stability of grain yield, protein content and quality, tive to normal-endosperm maize, the biological value and endosperm modification of QPM cultivars, we evaluated 18 single-(amount of N that is retained in the body) of QPM is cross, 18 three-way, and 18 double-cross hybrids, and eight openabout 80%, whereas that of normal maize is 40 to 57% pollinated cultivars (OPCs) grown at 13 tropical locations on four (Bressani, 1992). QPM has about 90% the biological continents. Hybrids averaged 13% higher grain yield than OPCs (5.97 and 5.17 Mg ha Ϫ1 ), whereas protein concentration in grain was 2% value of cow milk (National Research Council, 1988). greater for the OPC relative to hybrid cultivars (94.6 and 92.4 g kg Ϫ1 ).There is considerable debate, mostly centered around Endosperm modification score and tryptophan concentration in prothe issue of whether malnutrition is most often caused tein were similar for all cultivar types. Genotype ϫ environment interby calorie or protein deficiency, about the potential im- actions and sums of squares for deviations from linear regression (S 2 d )pact of QPM on alleviating human malnutrition. There for grain yield and protein concentration in grain were largest (indicatis ample evidence, however, that consumption of QPM ing least stability) for single-cross hybrids, followed by three-way, may help alleviate human malnutrition problems in re- double-cross, and open-pollinated cultivars (OPCs), successively. Thegions with maize-based diets (Bressani, 1992; Clark, reverse trend was observed for endosperm modification score, sug-1978; Mertz, 1992; National Research Council, 1988). gesting that more homogeneous cultivars had greater stability for thisAn alternative use of QPM is in feed rations for swine, trait. Additive main effects and multiplicative interactions (AMMI) analysis indicated that genotype ϫ environment interaction effectspoultry, or fish, where conventional sources of lysine, for grain yield and endosperm modification score were different for generally soybean m...

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Quality protein maize (Zea mays L.) (QPM) has protein of high nutritional value conferred by the opaque‐2 (o2) gene and vitreous endosperm because of numerous modifier genes. Superior protein quality is only expressed when endosperm tissue is homozygous recessive (o2o2). During QPM research and development, it is common to evaluate trials in which QPM genotypes randomly interpollinate. We do not know if protein quality determinations for entries in such trials are valid measures of what would be expressed in a pure stand. In this study, we used nine QPM and three o2 (unmodified, soft endosperm) cultivars as females for six pollen treatments to measure the effect of pollen source on protein concentration of grain, tryptophan concentration in grain, tryptophan concentration in protein, and endosperm modification (translucency) in three environments. The pollen treatments were four QPM hybrids, one normal‐endosperm maize cultivar, and self‐pollination. Pollen of normal‐endosperm maize reduced tryptophan in grain by 37% and tryptophan in protein by 38% but improved endosperm modification of QPM females by 36% relative to pollen of QPM males. Pollen of normal‐endosperm maize and QPM did not differ in effect on protein concentration of grain. Protein quality traits did not differ for QPM cultivars pollinated by self or by other QPM males. Kernels were slightly more vitreous, however, for females pollinated by other QPM males than for those that were self‐pollinated. Effects of females were significant (P < 0.01) and the interaction of males × females not significant for QPM entries for all traits. We conclude that it is valid to evaluate QPM germplasm in trials where entries randomly interpollinate, provided that pollen of normal‐endosperm maize is excluded.