Resistance of subspecies of Eucalyptus camaldulensis to galling by Leptocybe invasa: Could quinic acid derivatives be responsible for leaf abscission and reduced galling?

<p dir="ltr">Variability in galling caused by Leptocybe invasa Fisher & La Salle has been reported in several species and hybrids of Eucalyptus. Genetic diversity within Eucalyptus camaldulensis Dehnh. could confer resistance to L. invasa via variation in plant specialized metabolites or plant responses detrimental to insect herbivores. Moreover, optimal defence theory proposes that plants will invest more constitutive resistance in parts that are vulnerable to herbivore attack, such as immature leaves and apical buds, which are prone to galling. </p><p dir="ltr">We investigated constitutive resistance of subspecies and genotypes of E. camaldulensis to L. invasa while controlling for differences among growing conditions characteristic of their autochthonous Australian habitats using common nursery and garden arboreta plantings. Data on galling intensity, gall size, leaf phenolics and leaf physical attributes were used to investigate differences in susceptibility. We show that E. camaldulensis exhibits both constitutive and induced resistance to L. invasa. Intraspecific variability in galling was pronounced and correlated with concentrations of quinic acid derivatives and hypersensitive abscission of leaves. Whether these metabolites directly affect the survival of eggs or larvae remains to be determined. Hypersensitive leaf abscission in subspecies of E. camaldulensis in response to injury by a galling insect has not been reported previously and warrants investigation.</p>