Parental Selection of Hybrid Breeding Based On Maternal and Paternal Inheritance of Traits in Rapeseed (<i>Brassica napus</i> L.)

<div><p>Parental selection is crucial for hybrid breeding, but the methods available for such a selection are not very effective. In this study, a 6×6 incomplete diallel cross was designed using 12 rapeseed germplasms, and a total of 36 hybrids together with their parental lines were planted in 4 environments. Four yield-related traits and seed oil content (OC) were evaluated. Genetic distance (GD) was estimated with 359 simple sequence repeats (SSRs) markers. Heterosis levels, general combining ability (GCA) and specific combining ability (SCA) were evaluated. GD was found to have a significant correlation with better-parent heterosis (BPH) of thousand seed weight (TSW), SCA of seeds per silique (SS), TSW, and seed yield per plant (SY), while SCA showed a statistically significant correlation with heterosis levels of all traits at 1% significance level. Statistically significant correlations were also observed between GCA of maternal or paternal parents and heterosis levels of different traits except for SS. Interestingly, maternal (TSW, SS, and OC) and paternal (siliques per plant (SP) and SY) inheritance of traits was detected using contribution ratio of maternal and paternal GCA variance as well as correlations between GCA and heterosis levels. Phenotype and heterosis levels of all the traits except TSW of hybrids were significantly correlated with the average performance of parents. The correlations between SS and SP, SP and OC, and SY and OC were statistically significant in hybrids but not in parents. Potential applications of parental selection in hybrid breeding were discussed.</p></div

Double factors variance analysis of traits.

<p>G: genotype; E: environment; G×E: interaction of genotype and environment; DF: degree of freedom.</p><p>SS: seeds per silique; SP: siliques per plant; SY: seed yield per plant; TSW: thousand seed weight; OC: oil content in seeds; MPH: middle parent heterosis; BPH: better parent heterosis. The same abbreviations were used below.</p><p>** Significant at P = 0.01</p

Variance analysis of traits (By QGA station).

<p>A: additive effect; D: dominant effect; AA: interaction of additive and additive effect; AE: interaction between additive and environment effect; DE: interaction between dominant and environment effect; AAE: interaction of epistasis of additive and additive effect and environment effect.</p><p>** Significant at P = 0.01.</p

Phenotypic correlations between traits in hybrids and parents.

<p>The numbers in the upper or lower triangle are correlation coefficients between traits in hybrids, or between traits in parental lines.</p><p>* Significant at p = 0.05; ** significant at p = 0.01; n = 144.</p

Genetic distance between parental lines used for 6×6 incomplete diallel crosses.

<p>P1 to P6: maternal parents; P7 to P12: paternal parents.</p><p>P1, P2, P3, P7, and P8: cultivars (P1: ZS5; P2: ZS7; P3: ZS10; P7: ZS9; P8: HS5). P4 to P6, and P9 to P12: inbred lines.</p><p>See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0103165#pone.0103165.s001" target="_blank">Table S1</a> for detailed characteristics of the parental lines.</p

Heterosis level of incomplete diallel crosses.

<p>Heterosis level of incomplete diallel crosses.</p

Genetic parameters of heritability and combining ability.

<p>V_G: variance of general combining ability (GCA); V_S: variance of specific combining ability (SCA); V_gf: contribution ratio of the female GCA variance to the total variance; V_gm: contribution ratio of the male GCA variance to the total variance; V_gfm: contribution ratio of the SCA variance to the total variance; h²_b: broad sense heritability; h²_n: narrow sense heritability.</p

Correlation coefficients between GD, heterosis levels, and combining abilities of each trait.

<p>GD: genetic distance; GCA_f: GCA of female parents; GCA_m: GCA of male parents.</p><p>* Significant at p = 0.05; ** significant at p = 0.01.</p

Correlation coefficients of each trait between hybrid and its parental lines.

<p>** Significant at p = 0.01.</p

Correlation coefficients between heterosis level and average performance of parents.

<p>** Significant at p = 0.01; n = 36.</p