MYCOSPHAERELLA LEAF DISEASE - GENETIC-VARIATION IN DAMAGE TO EUCALYPTUS NITENS, EUCALYPTUS-GLOBULUS, AND THEIR F1-HYBRID

Severity of Mycosphaerella leaf disease was assessed on the adult and juvenile foliage of both controlled crossed and open-pollinated famili es of Eucalyptus globulus ssp. globulus Labill., Eucalyptus nitens (De ane & Maiden) Maiden, Eucalyptus globulus ssp. bicostata (Maiden, Blak ely & J. Simm.) Kirkpatr., and their F-1 hybrids in a trial in northwe st Tasmania, Australia. Within ssp, globulus, disease was more severe on one provenance, Taranna, than another, King Island. For interproven ance hybrids, differences between parents were inherited in an additiv e manner, whereas interspecific hybrids were generally more susceptibl e than predicted intraspecific midparent values and occasionally, were more susceptible than the more susceptible parent. Within populations , the narrow-sense heritabilities for Mycosphaerella disease severity were low to moderate (0.004-0.506), but were consistently higher for a dult than for juvenile foliage despite disease severity being higher o n juvenile foliage. Parental breeding values and heritabilities estima ted from open-pollinated progeny were similar to estimates obtained fr om controlled crosses involving the same parents. Complex genetic inte ractions were detected between growth, vegetative phase change, and di sease severity. It is possible that selection for rapid growth in an e nvironment without disease may result in indirect selection for suscep tibility.