Response to selection by yield and prolificacy at different environments in a tropical maize population

Three maize (Zea mays L.) selected populations, HB 21 A, MB 21 B, and MB 21 AB, were obtained after ten years of a selection program in which the original population, MB 21, was divided to be selected at three different environments. These environments were constituted using the two cropping seasons that are available in the Cauca Valley, a tropical Colombian region, where the research was conducted. Two of the environments corresponded to two cropping seasons: semester A, the less favorable environment for cropping: semester B, the more favorable environment for cropping; and the third included selection conducted in both the A and B semesters. Hence the AB population was selected for 20 cycles, whereas the A and B populations were selected for 10 cycles. Two traits, yield and prolificacy, were selected simultaneously, using independent culling levels. Changes in the phenotypic and genotypic properties of the three selected populations (A, B, AB) relative to the original MB 21 were evaluated through Design I (Comstocfc and Robinson, 1948) on each of the four populations. Testing of the progenies was conducted at one A and at one B semesters. Genetic parameters of yield and prolificacy, and some other traits, were estimated. Selection gains were estimated as the differences between selected and original populations. Most of phenotypic and genotypic changes caused by selection were intermediate for MB 21 A and MB 21 B and greatest for MB 21 AB. The observed gains for prolificacy were 2.31% (MB 21 A); 1.97% (MB 21 B), and