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

Interspecific hybridization between three Eucalyptus species with horticult ural merit, E. macrocarpa, E. pyriformis and E. youngiana, was undertaken t o investigate the likelihood of success of such crosses. All combinations p roduced fertile seed, with interspecific crosses as successful as intraspec ific. There were no differences between male species in fertility but there were differences between female trees within a species. Discriminant analy sis of each cross indicated a high degree of interspecific hybridization fo r hybrid 166 seedlings, with all except two seedlings clustering separately from a mixture of selfed and outcrossed seedlings of either parent, when m easured for a range of leaf and stem characters at three different nodes. T he success of this programme in producing both large numbers of seed and la rge numbers of hybrids indicated that it is possible that these species cou ld hybridize naturally if they were growing in the same location. It also d emonstrated the potential of controlled pollination, between closely relate d species of similar floral morphology, and seedling-based hybrid recogniti on as a method to produce eucalypt hybrids for further evaluation for comme rcial horticulture.