Identification of Quantitative Trait Loci Using a Small Sample of Topcrossed and F4 Progeny from Maize

Abstract

Plant breeders have an interest in the identification of genomic regions associated with the expression of quantitative traits because they recognize that such information could be used to improve realized heritability and reduce time per cycle of selection. The development of molecular marker technologies may provide tools to accomplish these goals. Maize (Zea mays L.) breeders develop new inbred parents of hybrids through top‐crossed and per se evaluation of numerous quantitative traits in segregating progeny from planned breeding crosses. This study was conducted to determine if regions of the genome associated with variability of agronomicaily important traits could be identified by a small, but typical, sample of top‐crossed and F2:4 progeny from the cross B73×MO17. We identified genomic regions in 24 agronomic traits, using interval mapping and simultaneous estimation of multiple quantitative trait locus models. The estimated numbers of quantitative trait loci (QTL) identified per trait were about three five. Many of the identified QTL were the same for correlated traits. Interestingly, yield QTL were not in the same regions previously reported for B73×MO17. This comparison contains a number of potential confounding factors: source of parental inbreds, type of progeny, different genotype × environment interaction effects, and different small samples of progeny from the cross. Consideration of these factors and the power of the tests to identify QTL suggests that the sampling of progeny is the most likely explanation for the differences.

Direct mapping of density response in a population of B73 × Mo17 recombinant inbred lines of maize (Zea Mays L.)

“…for heat units to anthesis in Beavis et al (1994) mapped to regions covered by our QTL for days to anthesis on chromosomes 1 and 8, and the effect of the B73 allele at these two QTL were consistent between studies. In addition, Beavis et al (1994) reported five QTL for grain yield (on a per unit surface area basis), three of which mapped to regions associated with barrenness, ear per plant, and yield per plant in our study.…”

“…In addition, Beavis et al (1994) reported five QTL for grain yield (on a per unit surface area basis), three of which mapped to regions associated with barrenness, ear per plant, and yield per plant in our study. The QTL for grain The ( þ ) indicates that the B73 allele at this QTL increased the value of the trait, (À) indicates that the B73 allele at this QTL reduced the value of the trait.…”

“…QTL for grain yield on chromosomes 2 and 9 in Beavis et al (1994) mapped to regions covered by a QTL for barrenness and a QTL for ears per plant in our study Figure 3. In both studies, the favorable alleles were Mo17 and B73 alleles, respectively.…”

“…Density response in maize M Gonzalo et al yield on chromosome 1 in Beavis et al (1994) mapped to a position spanned by the coverage region for the QTL for yield per plant (Figure 3), and in both cases, the B73 allele reduced yield. QTL for grain yield on chromosomes 2 and 9 in Beavis et al (1994) mapped to regions covered by a QTL for barrenness and a QTL for ears per plant in our study Figure 3.…”

“…The loci identified here can be compared by map position to loci earlier identified in B73 Â Mo17 mapping populations. F4 lines from this cross were studied by Beavis et al (1994). Two of the QTL Effects of replacing B73 alleles by Mo17 alleles for markers with significant marker by marker and/or marker by marker by density interactions estimated by fitting the best multiple marker model in the B73 Â Mo17 recombinant inbred line (RIL) population.…”