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 3 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.

Genome-wide mapping of QTL associated with heterosis in the RIL-based NCIII design

“…The two dimensional scanning methods, which consider both main and epistatic effects of pair QTL simultaneously with genetic background controlling, such as the mixed model approach of Wang et al [23] and inclusive composite interval mapping (ICIM) of Li et al [42], are alternative methods. However, the genetic design matrix should be reconstructed (Table 1) and the genetic parameter should be correctly explained [14][15][16]24,30,41]. Although the multiple interval mapping in Garcia et al [16] can estimate the augmented main and epistatic effects simultaneously, it differs from our method in two aspects.…”

“…Although the exploitation of heterosis in plant breeding is very successful, its genetic basis has been debated for more than 100 years and is still not completely resolved [12,19,30]. The genetic analysis of QTL can provide both molecular and practical understanding of this key phenomenon [8,15,19,28].…”

“…The additive QTL do not contribute to heterosis, while the non-additive QTL, including dominant, overdominant, and epistatic do contribute [12,15,19,22,24,25,28]. The second one is to use the measurements of heterosis as the data input to perform QTL analysis [13][14][15][24][25][26]30,43]. QTL effects for Z 1 and Z 2 in the RIL-based NCIII design provide estimates of the augmented effects a*, which measures the net contribution of the QTL to the parental difference, and d*, which measures the net contribution of the QTL to midparent heterosis [14].…”

“…QTL analysis was performed separately for the RIL, MPH of two backcross populations and the SUM (L 1 +L 2 ) and DIFF (L 1 −L 2 ) data of two backcross populations (L 1 and L 2 ). In the absence of epistasis, the analysis of RIL and SUM datasets identifies QTL with additive effect, whereas the analysis of MPH and DIFF datasets detects QTL with dominance effect [30]. Main-effect QTL was detected in each mapping population by composite interval mapping [27] and digenic interaction was identified in each mapping population by the mixed linear approach [23].…”

Metapopulation patterns of additive and nonadditive genetic variance in the sea bass (Dicentrarchus labrax)

“…Together with correlations between early survival, early growth, and observed proportions of females, this reflects a pleiotropic effect among traits, a pattern commonly assessed in cultured plants (e.g., Frascaroli et al., 2007; Fu et al., 2009). A positive genetic correlation between growth rate and a trend in expressing the female sex has been demonstrated earlier for the NAT population (Vandeputte et al., 2007), also supporting a pleiotropic effect on sex and growth in sea bass.…”