Genetic dissection of ear-related traits using immortalized F2 population in maize

Ear-related traits are often selection targets for maize improvement. This study used an immortalized F(IF) population to elucidate the genetic basis of ear-related traits. Twelve ear-related traits(namely, row number(RN), kernel number per row(KNPR), ear length(EL), ear diameter(ED), ten-kernel thickness(TKT), ear weight(EW), cob diameter(CD),kernel length(KL), kernel width(KW), grain weight per ear(GW), 100-kernel weight(HKW), and grain yield per plot(GY)),were collected from the IFpopulation. The ear-related traits were comprised of 265 crosses derived from 516 individuals of the recombinant inbred lines(RILs) under two separated environments in 2017 and 2018, respectively. Quantitative trait loci(QTLs) analyses identified 165 ear traits related QTLs, which explained phenotypic variation ranging from 0.1 to 12.66%. Among the 165 QTLs, 19 underlying nine ear-related traits(CD, ED, GY, RN, TKT, HKW, KL, GW, and KNPR)were identified across multiple environments and recognized as reliable QTLs. Furthermore, 44.85% of the total QTLs showed an overdominance effect, and 12.72% showed a dominance effect. Additionally, we found 35 genomic regions exhibiting pleiotropic effects across the whole maize genome, and 17 heterotic loci(HLs) for RN, EL, ED and EW were identified. The results provide insights into genetic components of ear-related traits and enhance the understanding of the genetic basis of heterosis in maize.

Genetic Components of Heterosis for Seedling Traits in an Elite Rice Hybrid Analyzed Using an Immortalized F2 Population

Utilization of heterosis has greatly contributed to rice productivity in China and many Asian countries. Superior hybrids usually show heterosis at two stages： canopy development at vegetative stage and panicle development at reproductive stage resulting in heterosis in yield. Although the genetic basis of heterosis in rice has been extensively investigated, all the previous studies focused on yield traits at maturity stage. In this study, we analyzed the genetic basis of heterosis at seedling stage making use of an ＂immortalized F2＂ population composed of 105 hybrids produced by intercrossing recombinant inbred lines （RILs） from a cross between Zhenshan 97 and Minghui 63, the parents of Shanyou 63, which is an elite hybrid widely grown in China. Eight seedling traits, seedling height, tiller number, leaf number, root number, maximum root length, root dry weight, shoot dry weight and total dry weight, were investigated using hydroponic culture. We analyzed single-locus and digenic genetic effects at the whole genome level using an ultrahigh-density SNP bin map obtained by population re-sequencing. The analysis revealed large numbers of heterotic effects for seedling traits including dominance, over- dominance and digenic dominance （epistasis） in both positive and negative directions. Overdominance effects were prevalent for all the traits, and digenic dominance effects also accounted for a large portion of the genetic effects. The results suggested that cumulative small advantages of the single-locus effects and two-locus interactions, most of which could not be detected statistically, could explain the genetic basis of seedling heterosis of the F1 hybrid.