ADAPTATION OF TROPICAL AND SUBTROPICAL MEXICAN RACES OF MAIZE TO TEMPERATE CLIMATE THROUGH VISUAL MASS SELECTION. YIELD, PLANT HEIGHT AND EARLINESS

Abstract

Maize breeding in the high valleys of Mexico destined to obtain improved open-pollinated varieties and hybrids has been limited to the use of the Conico and Chalqueño races. Introduction and a posterior adaptation of exotic germplasm is a valuable alternative to increase the genetic variability in a maize breeding program. Mass selection is an efficient method to improve high heritability characters, as well as grain yield. Ten tropical and subtropical maize races were visually mass selected for adaptation at Montecillo, State of México where temperate climate conditions prevail. The visual aspect of the plant and the ear were used as criteria for mass selection. The original variety, three visually mass selection composites (Cycle 3, Cycle 6 and Cycle 8 or 9) of each race, and five local varieties were evaluated at two locations during two years. The regression analysis applied to the four enviromentss showed significative changes in the three characters evaluated. Significant increases ranged from 2.6 to 24.7 % for ear yield per plant, while the number of days to tasseling decreased from 0.5 to 1.2 % in eight of ten races. Plant height changed in two directions: an increase in the range of 0.9 to 2.01 % in three races and a decrease in the range of 0.6 to 0.9 % in other three races, and there was no change in the remaining races. Visual mass selection was effective to adapt the ten exotic races to temperate climate conditions. The change in number of days to tasseling and plant
height due to selection occurred progressively so that magnitude of these traits equalled those of the local varieties. The most advanced
cycle of selection in the majority of the races surpassed significatively the ear yield of some local varieties.