Linkage Disequilibrium with Linkage Analysis of Multiline Crosses Reveals Different Multiallelic QTL for Hybrid Performance in the Flint and Dent Heterotic Groups of Maize

Abstract

Multiparental designs combined with dense genotyping of parents have been proposed as a way to increase the diversity and resolution of quantitative trait loci (QTL) mapping studies, using methods combining linkage disequilibrium information with linkage analysis (LDLA). Two new nested association mapping designs adapted to European conditions were derived from the complementary dent and flint heterotic groups of maize (Zea mays L.). Ten biparental dent families (N = 841) and 11 biparental flint families (N = 811) were genotyped with 56,110 single nucleotide polymorphism markers and evaluated as test crosses with the central line of the reciprocal design for biomass yield, plant height, and precocity. Alleles at candidate QTL were defined as (i) parental alleles, (ii) haplotypic identity by descent, and (iii) single-marker groupings. Between five and 16 QTL were detected depending on the model, trait, and genetic group considered. In the flint design, a major QTL (R 2 = 27%) with pleiotropic effects was detected on chromosome 10, whereas other QTL displayed milder effects (R 2 , 10%). On average, the LDLA models detected more QTL but generally explained lower percentages of variance, consistent with the fact that most QTL display complex allelic series. Only 15% of the QTL were common to the two designs. A joint analysis of the two designs detected between 15 and 21 QTL for the five traits. Of these, between 27 for silking date and 41% for tasseling date were significant in both groups. Favorable allelic effects detected in both groups open perspectives for improving biomass production. MOST traits of agronomic interest present a continuous variation resulting from the sum of the effects of various quantitative trait loci (QTL). Mapping these QTL is a first step toward elucidating their molecular nature and offers important application perspectives for marker-assisted breeding. QTL mapping started in plants with segregating families derived from the cross of two inbred lines (Lander and Botstein 1989). However, such biparental designs address only a small portion of the diversity available (a maximum of two alleles can segregate at a given QTL) and the accuracy of QTL positions is usually poor. To overcome these limitations, Rebai and Goffinet (1993) and Charcosset et al. (1994) proposed models for joint QTL detection in several biparental families connected to each other by the use of common parental lines. When the number of parents is less than the number of families, connections can be taken into account to reduce the number of allelic effects to be estimated in the detection model. This increases power and accuracy of detection when QTL behave additively (see Blanc et al. 2006). However, such a model makes the assumption that each parental line carries a different allele, which limits its benefit when the number of parental lines is high relative to the number of families, a situation commonly encountered in breeding programs. Recent advances in sequencing and genotyping technologies make it possi...

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