Additive genetic variance and covariance between relatives in wheat crosses with variable parental ploidy levels

Synthetic hexaploid wheat was developed and used in breeding to introduce new genetic diversity into bread wheat, through interspecific hybridization of T. tauschii (diploid) and durum wheat T. turgidum (tetraploid) to produce synthetic derivatives. Therefore, one may infer that the genetic variances of native wild populations vs. improved wheat may be different due differential origin and evolutionary history. We investigate this idea by partitioning the additive variance of grain yield with respect to breed origin using data from a synthetic derivative. Such information is needed to predict breeding values of synthetic derivatives and their parental populations. A mixed model with a heterogeneous covariance structure for breeding values was employed to estimate variance components using a program written by us. Data originated in a multi-year multi-location field trial of synthetic derivatives from the International Maize and Wheat Improvement Center (CIMMYT). Bayesian estimates of additive variances of grain yield from each population were similar for T. turgidum (0.0225) and T. tauschii (0.0208), but they were strikingly different from the one of T. aestivum (0.0131). Segregation variances were higher than zero, indicating differences in gene frequencies between pure breeds. Broad-sense heritability of the 25% synthetic derivative breed group was estimated to be equal to 0,66. Overall, our results support the suitability of models with heterogeneous additive genetic variances to predict breeding values in wheat crosses with variable ploidy levels.