Interspecific hybridization between three closely related ornamental Eucalyptus species: E. macrocarpa, E. youngiana and E. pyriformis

Abstract

Interspecific hybridization between three Eucalyptus species with horticultural merit, E. macrocarpa, E. pyriformis and E. youngiana, was undertaken to investigate the likelihood of success of such crosses. All combinations produced fertile seed, with interspecific crosses as successful as intraspecific. There were no differences between male species in fertility but there were differences between female trees within a species. Discriminant analysis of each cross indicated a high degree of interspecific hybridization for hybrid 166 seedlings, with all except two seedlings clustering separately from a mixture of selfed and outcrossed seedlings of either parent, when measured for a range of leaf and stem characters at three different nodes. The success of this programme in producing both large numbers of seed and large numbers of hybrids indicated that it is possible that these species could hybridize naturally if they were growing in the same location. It also demonstrated the potential of controlled pollination, between closely related species of similar floral morphology, and seedling-based hybrid recognition as a method to produce eucalypt hybrids for further evaluation for commercial horticulture.