COMBINING ABILITY AND HETEROSIS IN EARLY DEVELOPMENTAL STAGES OF MAIZE

An early establishment of maize (Zea mays L.) in the field is important to assure good yield at the end of the cycle, especially in the highlands of Mexico where planting is performed using the soil moisture from the previous season. To estimate the general combining ability (GCA) and heterosis at early stages of maize development, 15 progenitor landraces, their 105 crosses generated under a diallel array in conformity with a Griffing II design, and some additional native genotypes from the area of distribution of the Chalqueno race in the Mexican highlands, were evaluated. Planting was carried out under greenhouse conditions at a 15 cm depth using river sand as a substrate. The experimental design was a 12 X 12 square simple lattice with three replications. Traits recorded were speed and percentage of emergence, plant height, mesocotyl length and total biomass. There were differences (P <= 0.01) among groups and among populations within groups in the five traits. The populations Dgo-189, Gto-208, Gto-142, Col-03-64, Col-6784, FHCH-129F(10), Jal-335 and Tlax-151 presented the highest GCA values for emergence speed and total biomass. The highest heterosis was obtained with populations FHCH-129F(10), Col-03-64, Mex-633 and VS-22, when combined with Gto-208, Dgo-189, Jal-335, Tlax-151 and Oax-814. Crosses Jal-335 x Zac-66, Gto-142 x Zac-66 and Oax-814 x Gto-208 were outstanding also. Prominent crosses and populations were associated with opposite geographic sites, thus indicating that genetic divergence was associated with geographic divergence. The early vigor of new maize genotypes for Mexican highlands could be improved by involving some of the outstanding populations and crosses into the maize breeding programs.