Open-Pollinated and Synthetic Cultivars from Population Improvement

Abstract

Population improvement leading to open-pollinated or synthetic cultivars is a natural choice of breeding programme for out-breeding seed propagated crops. Construction of a foundation population is discussed. Predicted responses to mass selection and to half-sib, full-sib and S1 family selection are derived. Linkage disequilibrium, epistasis and the difference between immediate and equilibrium response are taken into account. Selection indices for more than one trait are introduced. Practical examples are drawn from maize, fodder kale, perennial ryegrass, alfalfa and clover. The results of the Illinois Long Term Selection Experiment in maize are presented and discussed in terms of selection limits and loss of desirable alleles by genetic drift. The theory and practice of constructing synthetic cultivars from improved populations is presented, including prediction of the best synthetic from the general combining abilities and S1 performance of the potential parents. Some autotetraploid theory is introduced for population improvement and synthetic cultivar production.