QTL mapping in testcrosses of flint lines of maize:: III.: Comparison across populations for forage traits

We mapped and characterized quantitative trait loci (QTL) affecting testcross performance of important forage maize (Zea mays L.) traits and investigated their consistency across different populations. Four independent populations comprising 380 F-3 lines (AXB(c)), 113 F-5 lines (AxB(v)), 131 F-4 lines (AxC(v)), and 140 F-4 Lines (CxD(v)) were produced from four elite flint inbreds (A, B, C, D) and genotyped at 89, 151, 104, and 122 RFLP marker loci, respectively. All lines were testcrossed to the same dent inbred tester and evaluated in field trials with two replications in five environments. Six traits were analyzed: dry matter yield (DMY), dry matter concentration (DMC), plant height (PHT), in vitro digestible organic matter (IVDOM), starch concentration (STC), and protein concentration (CPC) of for age. Genotypic variances (delta(g)(2)) were mostly significant for these traits in all populations and heritabilities generally exceeded 0.50. Between 2 and 14 QTL were detected in individual populations by composite interval mapping, which explained between 17.6 and 65.7% of the total phenotypic variance (ir:). Few of the detected QTL. displayed significant digenic epistatic or QTL x environment interactions. Consistency of QTL positions across all four populations was greater for DMC, STC, and PHT than for DMY, IVDOM, and CPC. Across all traits' QTL, results were largely consistent among AxB(c) and AxB(c), but not among AxB(c) and AxC(v) or AxB(c) and CxD(v). When QTL positions and substitution effects for DMY obtained in AxB(v), explaining 43% of delta(p)(2), were employed for prediction of QTL positions and substitution effects in the other three populations they explained 24% of sigma(p)(2) in AxB(v), 11% of sigma(p)(2) in AxC(v), and 0% of sigma(p)(2) in CxD(v). QTL results were poorly consistent among crosses, within the flint heterotic pool, suggesting that prior to marker-assisted selection, QTL mapping must be performed separately for each population.