Genomics of the Heterobasidion-Spruce Interaction as a Tool to Understanding Host Resistance

Root and butt rot of conifers caused by Heterobasidion is one of the most important tree diseases in the Northern hemisphere. Despite the high impact of Heterobasidion, ability to control the disease in forests with a long history of management is very li mited. Traits associated with resistance to pathogen growth appear to be highly heritable, and could be exploited in selection and breeding programmes. However, neither the molecular control nor the biochemical basis for this resistance is known in Picea species. This project will utilise state-of-the art genomics methods to elucidate gene regulation in Sitka spruce (Picea sitchensis) challenged with Heterobasidion annosum, in relation to lesion development and extension growth of the pathogen in bark and sapwood tissues. Responses of four mature Sitka spruce clones differing in susceptibility/resistance will be assessed after wounding and artificial inoculation with H. annosum at 0, 3, and 43 days after treatment. Bark and sapwood tissues surrounding the wounding and inoculation points will be used to pinpoint key constitutive and induced differences between resistant and susceptible host genotypes. Preliminary results of bark metabolomics have identified changes in the metabolome in spruce bark challeng ed with H. annosum. Key genes in metabolic pathways identified as upregulated in metabolomics will be examined in detail using gene expression analyses based on quantitative PCR. This project will increase our knowledge of the physiological processes inv olved in resistance of spruce to infection by Heterobasidion, enabling accurate and rapid identification of host genotypes showing greater resistance to the pathogen. Such resistant clones will be of very high value in breeding programmes, in forests havi ng high incidence of Heterobasidion and in the extensive afforestations now planned on agricultural land taken out of food production.