Protecting forest crops from disease: can comparative genomics provide management solution?

Commercial forest crops have lifespans measured in decades, but are equally susceptible to diseases as conventional short-lived food crops. An emerging problem is that the incidence of some foliar diseases is increasing due to climate change. For example, epidemics of Dothistroma needle blight (DNB) of pines in Europe and Canada are associated with increased rainfall. New methods of disease management are needed but difficulties inherent in working with this forest pathosystem have slowed progress. A breakthrough occurred recently when the genome of the DNB causal agent, Dothistroma septosporum, was sequenced by the Joint Genome Institute. Availability of the genome facilitated research that showed D. septosporum to be a hemi-biotroph rather than a necrotroph as previously supposed. Furthermore, the genome of D. septosporum is remarkably similar to that of the biotrophic tomato pathogen Cladosporium fulvum. Comparative analysis of genomes from these species revealed differences in genes for secondary metabolite biosynthesis and carbohydrate degradation that may help to determine host specificity. Genes common to the two species are also of interest. D. septosporum has putative effector genes that appear to be functional orthologs of the well-studied C. fulvum Avr and Ecp genes. Although resistant races are not well defined in pine populations, some pine species have R genes that function in a gene-for-gene manner in a rust pathosystem. This raises the possibility that candidate D. septosporum effectors, along with other similar gene products identified from the genome, may be used to screen for DNB resistance in pine accessions.