Classical genetic and quantitative trait loci analyses of heterosis in a maize hybrid between two elite inbred lines

Abstract

The exploitation of heterosis is one of the most outstanding advancements in plant breeding, although its genetic basis is not well understood yet. This research was conducted on the materials arising from the maize single cross B73 x H99 to study heterosis by procedures of classical genetic and quantitative trait loci (QTL) analyses. Materials were the basic generations, the derived 142 recombinant inbred lines (RILs), and the three testcross populations obtained by crossing the 142 RILs to each parent and their F(1). For seedling weight (SW), number of kernels per plant (NK), and grain yield (GY), heterosis was >100% and the average degree of dominance was >1. Epistasis was significant for SW and NK but not for GY. Several QTL were identified and in most cases they were in the additive-dominance range for traits with low heterosis and mostly in the dominance-overdominance range for plant height (PH), SW, NK, and GY. Only a few QTL with digenic epistasis were identified. The importance of dominance effects was confirmed by highly significant correlations between heterozygosity level and phenotypic performance, especially for GY. Some chromosome regions presented overlaps of overdominant QTL for SW, PH, NK, and GY, suggesting pleiotropic effects on overall plant vigor.

Figure 1.—

Regression analysis of phenotypic performance per se for plant height and grain yield on percentage of heterozygous molecular marker loci in TC(B) and TC(H) populations.

Figure 2.—

Bin allocation of the 21 QTL for grain yield showing overdominant (solid segments), dominant (segments with stripes), and partially dominant or additive (dotted segments) effects. Segments along the chromosomes represent the bins. QTL detected for the other heterotic traits—SW, PH, and NK—and colocating with those for grain yield are indicated in boldface type if they are overdominant, roman type if dominant, and italic type if partially dominant or additive.