Correlations and QTL Correspondence between Line Per Se and Testcross Performance for Agronomic Traits in Four Populations of European Maize

Abstract

The magnitude of the genotypic correlation between line per se performance (LP) and testcross performance (TP) is crucial for optimum testing schemes in hybrid breeding as well as simultaneous improvement of commercial hybrids and their inbred parents. The objectives of this study were to (i) obtain estimates of the correlation, and (ii) determine quantitative trait loci (QTL) correspondence between LP and TP within four populations (F 3 to F 6 lines) derived from intrapool crosses of European flint maize (Zea mays L.). The number of lines evaluated for both LP and TP ranged from 65 to 280 across the four populations. The LP and TP with a dent inbred tester were evaluated for grain yield, grain moisture, kernel weight, protein concentration, and plant height in four to five environments. Composite interval mapping (CIM) using a joint restriction fragment length polymorphism (RFLP) linkage map of all populations was conducted separately for LP and TP in each population, with sample sizes ranging from 71 to 344. Genotypic correlations between LP and TP, ? g (LP, TP), were low to intermediate for grain yield (0.28-0.56) across populations and intermediate to high for the other traits (0.52-0.87). The magnitude of ?g (LP, TP) across populations for grain yield was neither associated with the ratio between the genotypic variances for LP and TP nor with the evidence for dominance in LP or epistasis in LP or TP. Genotypic correlations between observed TP and its prediction based on QTL positions and effects for LP were smaller than corresponding values of ? g (LP, TP) for all traits. Except for grain yield, more than half of the QTL were in common to LP and TP in the largest population A × B'. Thus, it seems feasible to apply marker-assisted selection for TP based on QTL detected for LP, for traits with a large proportion of the genotypic variance accounted for by QTL.