Complex hybridity in Isotoma petraea. IV. Heterosis in interpopulational hybrids

Abstract

Discriminant analysis of four structurally homozygous populations of Isotoma petraea showed that they are significantly different with respect to phenotypes produced in a standardized environment and hence they are genetically different. These populations are relatively homozygous for different arrays of genes and their interpopulational hybrids exhibit a euheterotic increase in aerial dry weight. The individual natural populations may be considered as depressed inbred lineages of the relationally balanced base population of I. Petraea. The degree of heterosis observed in their interpopulational hybrids is mainly influenced by the degree of inbreeding that is characteristic of of each population. Negative heterosis was observed in interpopulational crosses among complex heterozygotes. The complex heterozygotes are genetically heterozygous, and a precise relational balance exists between the complexes associated in the native complex heterozygotes; this coadaptation does not extend from population to population.