Response to selection, combining ability and heritability of coleoptile length in winter wheat

Selection of winter wheat cultivars with long coleoptiles is an important component of improving emergence, weed suppression and grain yield in low rainfall regions of the world. Seven winter wheat cultivars were hybridized in a Griffing’s half-diallel mating design, method 2 (reciprocals excluded, parents included), model 1 (fixed), and the progeny analyzed for coleoptile length in the F₁ through F₄ for response to selection, general combining ability (GCA), specific combining ability (SCA) and heritability. Highly significant differences existed for GCA among progeny in each generation. SCA was highly significant in the F₁, F₂ and F₄, although SCA estimates were inconsistent among generations in each progeny population. The SCA/GCA ratio was 0.15, 0.11, 0.06 and 0.04 in the F₁ through the F₄, respectively, indicating that additive effects increased with homozygosity. Broad-sense heritability for coleoptile length was estimated at 0.86, 0.76, 0.60 and 0.78 for the F₁ through the F₄, respectively. Realized heritabilities ranged from −0.16 to 0.85 with a mean of 0.32 in the F₃ and ranged from −0.68 to 0.68 with a mean of 0.13 in the F₄. Spearman’s rank correlation coefficients (R_S) were significant for all generation comparisons except the F₁:F₂, indicating that changes in rank for coleoptile length were insignificant. Cultivars with long coleoptiles and high GCA were the best parents for improving coleoptile length. Sustained selection over generations for coleoptile length was more effective than one generation of selection for genotypes both with and without reduced height genes.