Selection for prolificacy in maize (Zea mays L.) populations

Author(s)

Andréa Pizaia

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2000-04-04
• Advisor: Jose Branco de Miranda Filho

Abstract

Prolificacy or the presence of two or more ears per plant is one of the main components of yield in maize. It provides high yield stability and higher efficiency in the utilization of nutrients by increasing the sink potential in the plant. The objective of this work was to evaluate the efficiency of two methods of intrapopulation recurrent selection for prolificacy and their relations with grain yield in six open-pollinated populations: PIRANÃO VD2B, PIRANÃO VF1B, PIRANÃO VF1B-P, IT A-PR, PICHILINGUE, and ESALQ-PR1; and add an study on the genetic characteristics of prolificacy. Populations were submitted to the methods designated as: a) S1 Selection, based on the development of S1 progenies by selfing the second ears of prolific plants; and b) IG Selection, based on the development of full-sib progenies through biparental crosses using the second ears of prolific plants. In the S1 Selection method, the selected progenies used for recombination were derived from phenotypic selection based on ear index of individual plants. In the IG Selection method the selected progenies used for recombination were selected on the basis of progeny means from experiments with replications following phenotypic selection of individual plants used in the biparental crosses. Two cycles of selection were completed and in each cycle progenies were evaluated in experiments with replications and data were used for estimating genetic parameters including the expected genetic gain. In the S1 Selection method the inbreeding effect shadowed the true expression of quantitative traits under evaluation but, in spite of that, overall results allowed to conclude that both methods were effective for increasing prolificacy in the populations under study. However, there was evidences that IG Selection is more effective for increasing prolificacy in populations with low initial expression for that trait because use full-sib progenies means and phenotypic selection. Population PIRANÃO VD2B, showed negative gain for prolificacy under S1 Selection. In the first cycle of selection the observed gains were 10,6% for IG Selection and -1,7% for S1 Selection, on the average of populations. Estimates of heritability and genetic variance for prolificacy were higher in the experiments of S1 progenies as compared to full-sib progenies; the reverse was observed for yield. The correlated response on yield after selection for prolificacy under IG Selection was 6,27% on the average. In the second cycle the average gains were 5,28% and 9,62% in IG Selection and S1 Selection, respectively. Inbreeding depression was lower for prolificacy than for yield in agreement with other reports that dominance effects are lower for prolificacy than for yield. (AU)