XVI International Botanical Congess

Hybridization between divergent lineages has long been assumed to produce unfavorable interactions between the parental genomes. These deleterious interactions have further been assumed to result in hybrid offspring with decreased levels of viability and/or fertility, thereby promoting post-mating reproductive isolation. More recently, evidence has emerged that interactions between divergent genomes may not always be deleterious. It now seems likely that crosses between divergent lineages can lead to the production of both fit and unfit hybrid genotypes. We investigated the role of nuclear and cytonuclear epistatis interactions in determining the outcome of crosses between two species of Louisiana iris. Overall, these crosses produced a significant deficit of intermediate hybrid genotypes accompanied by an excess of parental-like genotypes, suggesting that hybridization may indeed produce unfavorable genetic interactions. However, analyses of single and multi-locus segregation patterns revealed a variety of both negative and positive interactions at the nuclear and cytonuclear levels. These results suggest that the traditional view of uniformly deleterious interactions between divergent genomes is an oversimplification.