Genetic analysis in recombinant inbred lines of early dent forage maize. II - QTL mapping for cell wall constituents and cell wall digestibility from per se value and top cross experiments
Roussel, V.; Gibelin, C.; Fontaine, A.S.; Barriere, Y.
Maydica 47(1): 9-20
Quantitative trait loci (QTL) affecting feeding value traits in forage maize were evidenced and mapped in a recombinant inbred line (RIL) progeny from the cross between two early dent lines (F288 and F271) with contrasting cell wall digestibility. Traits studied were cell wall content and composition, whole plant digestibility and cell wall digestibility. Field experiments were conducted in Lusignan and Orne, France during 1998-2000; in Rennes during 1998; and in Lusignan, Le Pin and Mons during 1999-2000 to evaluate a set of 131 RILs per se and after top crossing with the early flint line F286. Heterosis was considered as the difference between the hybrid (RIL x F286) value and average value of the parents (RIL and F286 per se). The genotypic effects were highly significant and always greater than genotype x environment interactions. Transgressive lines were observed for digestibility traits only towards higher values in RILs, and only towards lower values in top cross. A map was achieved with 108 SSR markers, chosen to cover the entire genome. However, large monomorphic areas were found because the two parental lines were both related to line Co125. Putative QTL were identified through composite interval mapping, and are given for LOD values higher than 2.0. Additive x additive epistatic effects were investigated. QTL observed in RILs per se were logically more numerous than QTL found in top cross, but some QTL found in top cross were not found in RILs per se. QTL involved in heterosis for cell wall content or digestibility were also observed. Five major clusters of QTL were observed for digestibility and lignification traits. In descending order for their LOD values or percentage of explained phenotypic variation, the clustered QTLs were located in bins 6.06, 3.05, 2.08, 6.01 and 9.02. QTL for NDF, Hcell/NDF and Cell/NDF were also located in bins 2.08 and 6.06. QTL that are greatly involved in heterotic effects, both for digestibility traits and lignin content, were observed in bins 5.05 and 8.05. Significant simultaneous improvement of top cross yield, earliness, protein content and digestibility was proven to be possible by MAS based on the high yielding RIL no 143 and five other RILs, sources of favourable alleles for the respective traits under breeding.