Genetic resistance of Eucalyptus globulus to autumn gum moth defoliation and the role of cuticular waxes

This study investigated the association between resistance of Eucalyptus globulus Labill. to autumn gum moth (Mnesempala privata GuenevÉvÖe) defoliation and cuticular wax compounds. In a field trial consisting of clonally replicated F2 families of E. globulus, situated in Tasmania, Australia, significant genetic variation in resistance was detected in two of three F2 families. The broad-sense heritability for defoliation within families ranged from 0.24 to 0.33. The 15 most resistant and the 15 most susceptible genotypes within each variable family were compared for their relative levels of 26 cuticular wax compounds. While no significant correlation between resistance and total wax yield estimates was found, significant differences were detected between resistant and susceptible classes in the relative quantities of several aliphatic phenylethyl and benzyl wax esters within both families. This association does not appear to be a response induced by defoliation. The broad-sense heritabilities of the variation in these compounds were high (0.82-0.94). Our findings suggest that these wax compounds are a mechanism of genetic resistance to autumn gum moth in E. globulus.