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

Abstract

In the cooler temperate regions of the world, maize (Zea mays L.) is primarily cultivated for forage usage. In this study, we mapped and characterized quantitative trait loci (QTL) affecting testcross performance of important forage maize traits and investigated their consistency across environments and testers. Two elite flint inbred lines were crossed to generate 380 F2 individuals, 345 of which were genotyped at 89 RFLP (restriction fragment length polymorphism) marker loci. The 380 F3 lines obtained by selfing the F2 individuals and the parent lines were crossed to two diverse dent inbred testers. Each series of testcrosses (TC) was evaluated in field trials with two replicates in five environments. Five traits were analyzed: dry matter yield (DMY), dry matter concentration (DMC), plant height (PHT), starch concentration (STC), and starch yield (STY). Genotypic ( ) and genotype × environment variances were highly significant for all traits in both TC series. Heritabilities ranged from 0.64 to 0.88 except for STY (0.46, 0.47). Genotypic correlations between testers were high (>0.80) for all traits. QTL analyses were performed by composite interval mapping. Between seven (STY) and 16 (PHT) QTL were detected in each testcross series, explaining between 52 and 71% of all in a simultaneous fit. Few QTL displayed significant interactions with environments. Results were highly consistent across testers for DMC and PHT, but not for DMY, STC, and STY. Although a comparison of TC generation means indicated significant epistasis for DMY and PHT, significant interactions between QTL were detected in two cases only. If a genomic region simultaneously affected two characters, the increasing alleles for the individual traits originated in most cases from the same parent for positively correlated traits and from different parents for negatively correlated traits.