QTL Mapping in Testcrosses of European Flint Lines of Maize: II. Comparison of Different Testers for Forage Quality Traits

Abstract

Improving forage quality is a major goal in maize breeding for cooler climates. In this study, we mapped and characterized quantitative trait loci (QTL) affecting testcross (TC) performance of important forage maize quality traits and investigated their consistency across testers. Two elite flint inbred lines were crossed to generale 380 F2 individuals, 345 of which were genotyped at 89 RFLP marker loci. The 380 F3 lines produced by selfing the F2 individuals were testcrossed to two dent inbred testers. Each TC series was evaluated in field trials with two replications in five environments. The following six traits were analyzed: in vitro digestible organic matter (IVDOM), acid detergent fiber (ADF), metabolizable energy concentration (MEC), and protein concentration (CPC), all determined by near infra‐red reflectance spectroscopy (NIRS), as well as metabolizable energy yield (MEY) and protein yield (CPY). Genotypic variances (σ̂2g) mostly significant for these traits in both TC series. Heritabilities ranged from 0.24 to 0.69 and were low for IVDOM, ADF, and MEC. Genotypic correlations between testers exceeded 0.64 for each trait. Between four (CPY) and ten (CPC) QTL were detected in each TC experiment by composite interval mapping, explaining between 48.4% and 85.3% of σ̂2g in a simultaneous fit. QTL results were consistent across testers for CPC and CPY, but not for IVDOM, ADF, MEC, and MEY. Few of the detected QTL displayed significant digenic epistatic interactions. The digestibility traits IVDOM, ADF, and MEC were tightly correlated (|r̂g| > 0.88) with each other and displayed intermediate genotypic correlations (r̂g) with plant height and starch concentration, but low r̂g values with dry matter yield or dry matter concentration. In most cases, the magnitude of r̂g corresponded well with the number of common QTL regions affecting both traits.