YIELD, YIELD COMPONENTS AND HETEROSIS OF MAIZE GERMPLASM ADAPTED TO HIGHLANDS

Varieties of maize (Zea mays L.) introduced from other latitudes are a source of favorable alleles useful in plant breeding, but before being used they must be adapted to the climatic conditions of the target environments. The objective of this study was to evaluate the yield and its components in representative populations of tropical and subtropical maize races adapted by recurrent mass selection to the Mexican highlands, as well as the heterosis of their interracial crosses to identify genotypes useful for maize breeding in those environments. Nine adapted maize populations, eight crosses of two populations, one cross of three populations, advanced generations of the crosses and four commercial checks were evaluated. Genotypes were tested in three environments under a randomized complete blocks design with three replications. Grain yield and its components were recorded. Analysis of variance, comparison of means (Tukey, P <= 0.05), correlation analysis were performed and the heterosis was estimated in relation to the mid- parent. There were significant differences (P <= 0.01) between genotypes for all the traits; the adapted materials yielded from 3.89 to 11.71 t ha(-1) and the checks from 8.06 to 11.56 t ha(-1). The yield correlated with the prolificacy index (r = 0.67), ear length (r = 0.64), ear diameter (r = 0.65) and number of grains per row (r = 0.64). The average heterosis for yield and its components ranged from -5.30 to 6.53 %, with 5.68 % for yield, where the F-1 P9 x P8 cross showed the highest heterosis (26.19 %). Adapted populations and their crosses showed a performance similar to that of commercial checks; thus, they can be used by themselves or as participants for breeding local maize of highlands.