Selection Strategy in Breeding of Self-fertilizing Crops. :II. On the Use of Selection among F₂ Populations by the Presence and Absence of Promising Phenotypes

Abstract

Breeders seldom have enough time and labour to estimate the amount and nature of the genetic variation of segregating populations. Cross combinations therefore are assessed by the presence and absence of the promising phenotypes which appear to meet the breeding objective concerned. The application of this type of cross selection in F₂ is investigated to the conclusion that the breeding efficiency for a given breeding cost is increased by this selection ; F₂ populations should be entirely discarded if no promising" phenotype is found regarding qualitative characters and some continuous characters which are easily assessed and as heritable as regularly show significant correlations between F₂ plants and F₃ progenies. This holds even with a relatively small population size as 500-1, OOO and in the presence of a negative but not very close genetic association between these characters and the ones which also are concerned with the breeding objective but not assessed in F₂' With a large F₂ population, the selection among and within crosses is useful even when the characters are negatively and closely associated. The direct measurement of yield in F₂ as still proposed by some workers is not expected to be rewarding.