Date of Award
Doctor of Philosophy
Arnel Roy Hallauer
Mass selection for yield and prolificacy, using independent culling levels, was made in a Colombian maize (Zea mays L.) population, MB 21, which corresponds to an advanced crossing of ETO x USA 342 (West Indian Composite). The research was conducted in Palmira, Colombia for 10 years, using three environmental situations: selection at the A semester, the less favorable cropping season, selection at the B semester, the more favorable cropping season, and selection at both the A and B semesters;Changes in the three populations developed (MB 21 A, MB 21 B, and MB 21 AB), respect to the original population (MB 21), were evaluated in two seasons (A and B semesters), using Design I. The means of prolificacy and yield, and other correlated traits (ear height, days to silk, ear weight, and grain moisture at harvesting) increased with selection. Greater gains were achieved with selection in both semesters (AB). Selection at the less favorable environment (semester A), on the average, produced better results than the selection at the more favorable environment (semester B). Gains by year for prolificacy were 2.3, 2.0, and 3.8%, for MB 21 A, MB 21 B, and MB 21 AB, respectively. For yield those gains were 3.8, 3.4 and 5.3%;The additive genetic variance for prolificacy increased in each of the selected populations. For yield the additive genetic variance was greater in MB 21 AB, and smaller in MB 21 A and MB 21 B populations. The heritability on a plot basis for yield and prolificacy was reduced in the selected populations. Selection at the less favorable environment (semester A) reduced the additive genetic x environmental effects for yield, whereas selection at the more favorable environment (semester B) increased those effects. Expected gains were higher than realized changes, particularly in the testing A semester, which would indicate that the additive genetic variances were overestimated;The efficiencies of the indirect responses showed that the correlated response due to selection at the less favorable environment was at least equal to the direct response for selection at the best environment. It was suggested that additional gains from selection could be realized if off-season nurseries and stations were used in selection programs. Selection for yield was more efficient to increase the level of prolificacy than vice versa. Selection for the two traits, however, was more efficient than selection for yield only.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
José Ever Vargas-Sánchez
Vargas-Sánchez, José Ever, "Response to selection by yield and prolificacy at different environments in a tropical maize population " (1990). Retrospective Theses and Dissertations. 9415.