Barriers to the production of interspecific hybrids in Eucalyptus
Potts, BM and Volker, PW and Dungey, HS, Barriers to the production of interspecific hybrids in Eucalyptus, Proceedings of the AFOCEL-IUFRO Symposium, 14th-8th September, Bordeaux, France, pp. 193-204. (1992) [Refereed Conference Paper]
A detailed knowledge of crossability patterns is essential for the effective use of a hybrid breeding strategy as
reproductive barriers may preclude many otherwise desirable species combinations from direct commercial
exploitation. The major eucalypt subgenera are reproductively isolated and, despite natural bybridisation being
relatively common, there is evidence for post-mating barriers of varying strength within subgenera. Many
hybrid combinations result in high levels of deleterious abnormalities which may be expressed at various stages
of the life cycle. Even in the case of hybridisation amongst the closely related species Eucalyptus globulus, E. nitens and E. bicostata, the level of deleterious abnormalities was significantly greater than outcross and inbred
controls. Abnormalities in hybrid families were clearly evident in the nursery whereas the deleterious effects of
inbreeding only became significant after 1 years' plantation growth. An optimum level of divergence associated
with inter-provenance crossing was apparent for cross success and early growth. The expression of deleterious
abnormalities in specific hybrid families was not predictable on the basis of the intraspecific performance of the
parents and appears to be due to a different genetic mechanism to that resulting in inbreeding depression. The
implications of such findings for hybrid breeding are addressed. In the case of the temperate species examined.
the successful use of hybrids will depend on the development of efficient methods of clonal propagation as the
operational production of Fl hybrid seed appears prohibitive.