Hybrid performance and species crossability relationships in willows (Salix)

Abstract

Interspecific hybridization between Salix amygdaloides Anderss., S. bebbiana Sarg., S. discolor Muhl., S. eriocephala Michx., S. exigua Nutt., S. lucida Muhl., S. pellita Anderss., and S. petiolaris Smith revealed several forms of postzygotic inviability including seed incompatibility, seedling inviability, inferior growth performance, and reduced fertility in the F1 hybrid progeny. The proportion of inviable and inferior progeny varied with the species combination and the specific combining ability of genotypes within each species combination. Family mean growth performance was lower in most interspecific hybrids, but several hybrid combinations produced progeny superior to the average performance of intraspecific crosses involving the same parent species. Interspecific hybrid families were also characterized by high proportions of nonflowering individuals. Viable F1 interspecific hybrids generally suffered reduced male and female fertility, but most female F1 hybrids produced viable open pollinated seed. The relatively high fertility and viability demonstrated by some interspecific hybrids indicates that natural interspecific gene flow between several species of subgenus Vetrix is possible. Crossability relationships based on F1 hybrid viability suggest that Salix exigua is more closely related to species of subgenus Vetrix than to those of subgenus Salix.