Mycosphaerella leaf disease: genetic variation in damage to Eucalyptus nitens, Eucalyptus globulus, and their F1 hybrid

Severity of Mycosphaere/la leaf disease was assessed on the adult and juvenile foliage ofboth controlled crossed and open-pollinated families ofEucalyptus globulus ssp. globulus Labill., Eucalyptus nitens (Deane & Maiden) Maiden, Eucalyptus globulus ssp. bicostata (Maiden, Blakely & 1. Simm.) Kirkpatr., and their F1 hybrids in a trial in northwest Tasmania, Australia. Within ssp_ globulus, disease was more severe on one provenance, Taranna, than another, King Island. For interprovenance hybrids, differences between parents were inherited in an additive manner, whereas interspecific hybrids were generally more susceptible 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 adult than for juvenile foliage despite disease severity being higher on juvenile foliage. Parental breeding values and heritabilities estimated from open-pollinated progeny were similar to estimates obtained from controlled crosses involving the same parents. Complex genetic interactions were detected between growth, vegetative phase change, and disease severity. It is possible that selection for rapid growth in an environment without disease may result in indirect selection for susceptibility.