Constitutive and inducible defense in Eucalyptus determines the feeding host of Gonipterus platensis, denoting specific plant-insect coevolution and a strategy for resistance improvement

Defoliation caused by Gonipterus platensis on Eucalyptus seriously impacts tree growth rate and forest production. The weevil's feeding preference has sometimes limited which species of Eucalyptus to plant, although the plant's metabolic features that govern such choice still need to be uncovered. We used metabolomics to reveal the chemical traits mediating this interaction, focusing on a model formed by two Eucalyptus species with markedly different susceptibility, E. globulus (susceptible), and E. nitens (resistant). Our results suggest that the insect's feeding preference strongly depends on the Eucalyptus species' constitutive metabolome, especially on the stilbenes and hydrolysable tannins accumulation. The susceptible E. globulus could not produce such classes of metabolite either constitutively or after herbivory, which indicated an apparent lack of critical enzymes for biosynthesis of these substances, such as stilbene synthase (STS) and gallate 1-beta-glucosyltransferase. On the other hand, it seems that no matter how toxic the systemic defense induced in E. globulus after herbivory could be to an insect, counteradaptations, apparently evolved by the weevil, may efficiently detoxify them. This may result from plant-insect coevolution, given their common geographical origin. Inter-specific hybridizations between E. nitens and E. globulus have adapted hybrid species better to low temperatures and frost conditions, consequently being propagated for plantations in temperate regions. Thus, this research lays the groundwork for selecting the best parent genotypes and obtained hybrids, aiming to warrant the transfer of key resistance traits to progenies as an attractive strategy for future breeding programs.