Predicting progeny means and variances of winter wheat crosses from phenotypic values of their parents

The efficiency of breeding programs could be increased by predicting the prospects of crosses for line development before producing and testing lines derived from them. In this study, we examined the performance of F_4:n (n = 7 or 8) lines randomly derived from 30 winter wheat (Triticum aestivum L.) crosses produced by a factorial mating of five high yielding with six high baking quality cultivars. Our objectives were to (i) contrast the midparent value m̂_ij with ĉ_ij for each cross and apply tests for the presence of epistasis, (ii) compare the estimates of the variance between means of crosses (σ_c²) with the average segregation variance within crosses σ_g² (iii) determine the variation in σ_gij² among crosses, (iv) evaluate the use of various parameters for predicting C_ij, σ_gij², and U_ij, and (v) briefly describe quantitative-genetic theory for interpretation of our experimental findings. Twenty-two lines per cross and the respective parents were evaluated in four environments for seven agronomic and quality traits. Additionally, 44 F_2:4 lines per cross were tested in hills in two environments. On the basis of first-degree statistics, parental means were good predictors of cross means, yet significant epistatic effects were observed for most traits. In agreement with quantitative-genetic expectations, the genetic variance between σ_c² was of the same size as the variance between parental means and the average σ_g² of F_4:n lines within crosses for all traits but sedimentation. Here, the two parental groups differed significantly in their mean, and σ_g² was significantly larger than σ_c². Estimation of the segregation variance (σ_gij²) for individual crosses is not recommended because they (i) have a large standard error, (ii) can be assessed reliably only in advanced selfing generations, and (iii) are expected to have a minor influence on differences in the usefulness among crosses. Among all predictors investigated, only the parental means can be recommended for predicting the usefulness of crosses.