Breeding and Genetics SOME CURRENT ISSUES IN POPULATION GENETICS IN RELATION T O SUGARCANE BREEDING A

Four topics in modern population biology, namely, genetic architecture, stability, diversity and allozyme flexibility, are discussed in relation to sugarcane breeding. It is argued that research on the following points is likely to improve sugarcane breeding: 1) Repeated cycles of intercrossing and selection of different modes can be specifically designed to elucidate the genetic architecture of economic traits. 2) To assess the merit of a particular entry (either a monoor a multi-genotypic variety), a tripartite measure of its performance over varying environments should be used. This measure is the overall mean, the coefficient of regression on environmental favourability and the deviation from regression. 3) From a set of genotypes, the subset which survives a period of mixed cultivation and selection is liable to outyield the original set because economic merit and competitive ability are likely to be positively related. Furthermore, the surviving genotypes are more likely to be able to grow together as a mixed stand because mutual selection has been given a chance to operate. 4) Genetic variation in enzymes offers not only genic markers for studying the effects of population processes, but also possible components of fitness.