Selection Strategy in Breeding of Self-fertilizing Crops : I.Theoretical Considerations on the Efficiency of Single Plant Selection in Early Segregating Generations

Abstract

The condition for effective single plant selection in early generation is defined.Numerical computations show that the condition is satisfied not only for qualitative characters but also for the continuous characters which are assessed as easily as and are as heritable as heading date and some characters related to plant height and plant type. Early selection is remarkably advantageous for the characters where promising genotypes are highly selectable compared to unpromising ones. This holds even in the presence of a negative but not very close genetic association between these characters and others which are not assessed in early generations. Comparison is made between the two selection systems; the early selection system where plants with promising phenotypes for heritable characters are selected in F2 generation using a sufficiently large population, and the delayed selection system as the bulk breeding method in Japan, where early populations are generation-advanced, neither plant nor cross selection being carried out until F4 or later generations. It is shown that a larger chance of success with a given breeding cost (including time and labour) is achieved by a breeding system incorporating early selection.