Relative performance of testers to identify elite lines of corn (Zea mays L.)

Testcross evaluation is used to determine the relative potential of corn (Zea mays L.) lines in a hybrid breeding program. Choice of tester is important for efficient selection among lines for their potential in hybrids. Testcrosses among 21 lines and seven testers were evaluated at seven environments in Guatemala. The experimental design was a randomized complete block with a split-plot arrangement, where lines were assigned to whole plots and testers to subplots. The objectives of the study were to obtain information for choice of testers and to identify the more convenient tester to use in early testing for a hybrid program in which three-way and double-cross hybrids are commonly used. Data for yield and agronomic traits were recorded, but the combined analysis for yield (t/ha) was the main trait of interest. Differences among lines and among testers across environments were highly significant (P ≤ 0.01). Highly significant differences for the testers x lines interaction indicated that the testers ranked the lines differently. Coefficient of concordance (W) and Pearson correlations (r) suggested that the ranking of lines across testers was relatively consistent. Testcrosses with a single cross had the greatest average yield (6.48 t/ha). Based on the variance among testcrosses, estimates of general combining ability, correlation with the other testers, and acceptable performance itself, the single cross tester was suggested as the tester for the hybrid breeding program in Guatemala. Lines with good general combining ability for different hybrid combinations were identified. Three-way testcrosses superior to the best check (ICTA HB-85) were identified for further evaluation as potential new hybrids for release. Significant correlations between yield and diseases (Southern corn rust caused by Puccinia polysora Underw. and Northern corn leaf blight caused by Exserohilum turcicum Pass. = Helminthosporium turcicum Pass.) reflected the importance of emphasizing selection for disease resistance during line development.

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