DIVERGENT MASS SELECTION FOR TIME TO ANTHESIS IN A MAIZE (ZEA MAYS L.) POPULATION (BREEDING, RECURRENT, GENETIC)

The objective of this study was to determine the correlated and direct responses to divergent mass selection for days-to-anthesis (DTA) in a Mexican land-variety belonging to the race Chalqueno. Ten cycles of selection and evaluations were conducted at Chapingo. The tenth (final cycle) also was evaluated at College Station. A combined analysis involving data collected from six evaluations of Chapingo, was done.;There was a positive correlated response to days-to-silking, for plant height, ear height and grain moisture at harvest time in both late and early selections: but there was a negative correlated response for grain yield in both directions in the evaluations at Chapingo.;The basic reasons for these results are: (1) late selections were too late for the growing season as the extremely low temperature reduced the efficiency of the "source" to fill the "sink"; and (2) early selections had an increased grain yield because grain filling period occurred under a more favorable environment.;The response of DTA to selection in both directions was significant in all evaluations from 1976 to 1982. However, there was asymmetry in response, lateness direction being about three times that of earliness direction. The total response in DTA over six evaluations in Chapingo was: 42.5% at a rate of 4.04% (+OR-) 0.21 per cycle in the lateness direction and - 11.7% at a rate of -1.38% (+OR-) 0.21 per cycle in the earliness direction. In addition, DTA of F(,1) crosses (between later by earlier selections) was found to be exactly intermediate between parents. The high linear response to selection in both directions and the intermediate F(,1) values, suggested an average additive effect of the genes controlling DTA. Realized heritability for DTA was 0.25 (+OR-) 0.03 in the laterness direction and 0.19 (+OR-) 0.02 in the earliness direction and 0.24 (+OR-) 0.02 for divergence (later - earlier) values. Both accumulated GDD and photoperiod were major determinants in DTA response in all evaluations.