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Heterosis and Combining Ability of CIMMYT's Quality Protein Maize Germplasm: II. Subtropical

Int. Maize and Wheat Improvement Ctr. (CIMMYT), Lisboa 27, Apdo. Postal 6–641, 06600, México D.F., Mexico

^* Corresponding author.

Information on the combining ability and heterotic patterns of CIMMYT's maize (Zea mays L.) germ plasm is of great value to maize breeders worldwide, for hybrid development. The objective of this study was to determine the heterosis and combining ability of CIMMYT's subtropical quality protein maize (QPM) germplasm, and to identify suitable germplasm for hybrid development. Six QPM gene pools and four QPM populations were used to make a 10-parent diallei. Parents and the 45 crosses were tested in three environments in Mexico and three in the USA. Highly significant (P < 0.01) differences were observed among entries, parents, and crosses for grain yield, time to silk, plant height, and endosperm hardness in Mexican environments, and for grain yield, ear height, and time to silk in U.S. environments. General combining ability (GCA) effects were highly significant for all traits, while specific combining ability (SCA) effects were nonsignificant (P > 0.05). Population 68 QPM was the highestyielding parent (6.99 Mg ha^-1) in Mexican environments, and Pool 31 QPM was the highest yielding (4.65 Mg ha^-1) in U.S. environments. The highest-yielding crosses were Pool 32 QPM x Population 68 QPM (7.05 Mg ha^-1) in Mexican and Pool 29 QPM x Population 70 QPM (5.12 Mg ha^-1) in U.S. environments. Under Mexican environments, Population 68 QPM and Pool 32 QPM among whites and Population 69 QPM and Pool 34 QPM among yellows were the best general combiners for grain yield. For endosperm hardness, the best combiners were Pool 33 QPM, Population 69 QPM, and Pool 31 QPM, all of which have flint grain type. Under temperate U.S. conditions, the two early-maturity gene pools (Pool 27 QPM and Pool 29 QPM) and Population 70 QPM were the best combiners for grain yield. For subtropical conditions, Population 68 QPM, Pool 32 QPM, Population 69 QPM, and Pool 34 QPM hold potential for hybrid development. These are hard endosperm opaque-2 (o2) parents (except for Pool 34 QPM, a partially modified parent). For temperate breeding programs in the USA, Pool 27 QPM, Pool 29 QPM, and Population 70 QPM could be used as exotic germplasm sources for introgression into U.S. Corn Belt QPM materials and for developing hard endosperm QPM hybrids.

Received for publication May 13, 1992.

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