Predicted genetic gain and inbreeding depression with general inbreeding levels in selection candidates and offspring

Authors: Edwards, Jode

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2008
Publication Date: 11/1/2008
Citation: Edwards, J.W. 2008. Predicted Genetic Gain and Inbreeding Depression with General Inbreeding Levels in Selection Candidates and Offspring. Crop Science. 48:2086-2096.

Interpretive Summary: Hybrid seed corn production is a very costly process for the U.S. seed industy because hybrid seed corn is produced from pure-line corn cultivars called inbreds. Inbreds have susbtantially lower yields that other types of corn, and thus much land space is required to produce hybrid seed corn. Very efficient plant breeding methods have been developed for the improvement in yield of hybrid corn, very little is known about efficiently improving the yield of inbred lines used as parents of corn hybrids. The present study was undertaken to develop mathematical prediction models to predict the effect of various breeding methods on the improvement of productivity of inbred lines. Such equations will be used by plant breeders to compare different methods of breeding in order to choose the best method for improving the productivity of corn inbred lines. The equations developed can be applied to any crop species for which hybrid cultivars are grown. The primary customers of this research will be seed companies and seed producers. Consumers will also benefit from reduced cost of hybrid seeds.

Technical Abstract: Methods for predicting response in noninbred populations to recurrent selection methods for half-sib and self-progeny families has been very well developed in the literature. However, theory to predict improvement of inbred lines derived from a recombined population, as well the predicted change in inbreeding depression rate has not been developed. Prediction equations for general levels of inbreeding in both candidate families and response units was developed. All common methods of half-sib and self-progeny recurrent selection were predicted to change inbreeding depression rates in a population if the covariance parameters D1 and D2* were nonzero. The change in inbreeding depression rate was unaffected by additive genetic variance. The theory highlighted the difficulty in defining breeding value consistently across inbreeding levels.