COMBINING ABILITY FOR YIELD AND PROTEIN-QUALITY AMONG MODIFIED-ENDOSPERM OPAQUE-2 TROPICAL MAIZE INBREDS

The opaque-2 mutation has been used in maize (Zea mays L.) breeding to develop cultivars with increased concentrations of lysine and tryptop han. Very little information is available, however, about combining ab ility for protein quality traits for modified/vitreous-endosperm opaqu e-2 maize (quality protein maize, or QPM), although such information i s essential for planning an effective hybrid development program. This research assessed the relative importance of general and specific com bining ability effects (GCA and SCA) for grain yield, protein concentr ation in grain, tryptophan concentration in grain, and tryptophan conc entration in protein for various tropical, late maturity, white graine d QPM lines. Four diallel trials, involving a total of 28 lines from f ive 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 yiel d, 48% for tryptophan concentration in grain, and 60% for tryptophan c oncentration in protein. Mean squares for GCA effects in across-locati on analyses were significant (P < 0.05) for grain yield, protein conce ntration in grain, and tryptophan con centration in protein for three of the four trials, and for tryptophan concentration in grain in two t rials. Mean squares for SCA effects were not significant except for gr ain yield in one diallel. Location x GCA interaction was generally sig nificant for all traits except tryptophan concentration in protein. Ou r results suggest that QPM hybrids with the highest values for protein quality traits will be crosses between lines with the highest GCA val ues. Concurrent improvement of yield and protein quality should be pos sible for this germplasm because phenotypic correlation coefficients w ere not significant for grain yield with concentration of protein in g rain, concentration of tryptophan in grain, and concentration of trypt ophan in protein.