Evaluation of heterotic patterns in developing maize hybrids for middle-altitude regions of Mexico.

This research was carried out to evaluate and characterize several heterotic patterns as a breeding strategy for developing hybrids for the Bajio region in Mexico. It was based on the performance of the crosses made, in the estimation of the type of gene action within each heterotic pattern, and the proportion of high yielding hybrids for intermediate or middle-altitude regions of Mexico. The genetic material evaluated included three heterotic groups: Tropical x Bajio (TxB); Dwarf x Normal (DxN), and Early x Late (ExL), with 20 hybrids each one and two commercial controls recommended for the region. Hybrids were developed using a nested mating design, where each of five males was crossed with four females. Hybrids were considered as full-sibs, and then, utilized for the genetic characterization of the groups or heterotic patterns. Data were recorded for ear yield at 15,5% moisture content, days to anthesis, days to silking and plant height. Hybrid evaluation was conducted in two representative locations of middle-altitude (1100 to 1900 masl) regions during the spring-summer season of 1995 at Celaya, Gto.and Sandia el Grande, N.L. Results showed that the ExL pattern produced hybrids having the best agronomic traits and the highest genetic variance. Due to the intrinsic asynchrony difficulties it was concluded that the DxL pattern was the best strategy for developing hybrids for the middlealtitude regions of Mexico.