Abstract

Heterosis contributes a big proportion to hybrid performance in maize, especially for grain yield. It is attractive to explore the underlying genetic architecture of hybrid performance and heterosis. Considering its complexity, different from former mapping method, we developed a series of linear mixed models incorporating multiple polygenic covariance structures to quantify the contribution of each genetic component (additive, dominance, additive-by-additive, additive-by-dominance, and dominance-by-dominance) to hybrid performance and midparent heterosis variation and to identify significant additive and non-additive (dominance and epistatic) quantitative trait loci (QTL). Here, we developed a North Carolina II population by crossing 339 recombinant inbred lines with two elite lines (Chang7-2 and Mo17), resulting in two populations of hybrids signed as Chang7-2 × recombinant inbred lines and Mo17 × recombinant inbred lines, respectively. The results of a path analysis showed that kernel number per row and hundred grain weight contributed the most to the variation of grain yield. The heritability of midparent heterosis for 10 investigated traits ranged from 0.27 to 0.81. For the 10 traits, 21 main (additive and dominance) QTL for hybrid performance and 17 dominance QTL for midparent heterosis were identified in the pooled hybrid populations with two overlapping QTL. Several of the identified QTL showed pleiotropic effects. Significant epistatic QTL were also identified and were shown to play an important role in ear height variation. Genomic selection was used to assess the influence of QTL on prediction accuracy and to explore the strategy of heterosis utilization in maize breeding. Results showed that treating significant single nucleotide polymorphisms as fixed effects in the linear mixed model could improve the prediction accuracy under prediction schemes 2 and 3. In conclusion, the different analyses all substantiated the different genetic architecture of hybrid performance and midparent heterosis in maize. Dominance contributes the highest proportion to heterosis, especially for grain yield, however, epistasis contributes the highest proportion to hybrid performance of grain yield.

Highlights

  • Heterosis is the phenomenon that a hybrid outperforms its two parents (Birchler et al, 2006; Lippman and Zamir, 2007)

  • We developed a North Carolina Design II (NCII) population of maize by crossing a set of 339 recombinant inbred lines (RILs) with two elite inbred lines, resulting in two populations of hybrids

  • A RIL population consisting of 365 F11 lines was developed by crossing inbred lines Qi319 as the male parent and Ye478 as the female parent originating from two different heterotic groups of maize (Zhou et al, 2016)

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Summary

Introduction

Heterosis is the phenomenon that a hybrid outperforms its two parents (Birchler et al, 2006; Lippman and Zamir, 2007). Many studies were performed to test these hypotheses, but the results often varied, depending on the populations and the traits studied, suggesting that heterosis is a complex genetic phenomenon. One commonly used design to study heterosis is the North Carolina Design III (NCIII) or Triple Testcross Design which allows to estimate the contribution of additive, dominance, and epistasis effects to heterosis (Melchinger et al, 2007b; Garcia et al, 2008). The analysis of hybrid maize data from another NCIII design showed that dominance loci contributed the most to heterosis in maize, while the additiveby-additive effects contributed the most to the heterosis of rice (Garcia et al, 2008)

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