Dothistroma septosporum (sexual stage: Mycosphaerella pini) is a foliar pathogen of many pine species throughout the world, causing serious economic losses. The incidence and severity of Dothistroma needle blight has increased dramatically in Canada and Europe since the mid 1990s, with climate change a major factor in the occurrence of these epidemics. The disease now causes widespread mortality and growth losses in natural native forests as well as in commercial plantations, with consequent implications for carbon sequestration. Understanding this foliar pathogen at the genome level is critical to developing new methods to manage the disease.
The study of forest pathogens has never been more urgent. Forests have undisputed economic and ecological importance, and some tree species, including pines, are potential rich sources of biomass for biofuel as well as being carbon sinks. Pines account for the majority of commercial forest products in many countries, including the southern USA (Pinus taeda), New Zealand, Australia, Chile (P. radiata), and South Africa (P. patula) and are an important component of native forests in many regions including North America, Asia, and Europe. Loblolly pine (Pinus taeda) EST sequencing is currently in progress at JGI. The availability of genome data from P. taeda as well as D. septosporum will provide unprecedented insights into how the Dothistroma pathogen interacts with its host. Furthermore, comparative analysis of the D. septosporum genome with genomes of related fungi in the Class Dothideomycetes will enable identification of common genes, such as effectors, involved in host-pathogen interactions, as well as genes that are unique to D. septosporum. It is anticipated that a genetic profile that distinguishes forest foliar pathogens from foliar pathogens of other crops can be determined.
Study of the D. septosporum genome will also provide insights into the biosynthesis of toxic fungal secondary metabolites. Dothistromin, a toxin produced by D. septosporum, is a close chemical relative of aflatoxins that contaminate some food crops and cause serious health concerns. Aflatoxin biosynthetic and regulatory genes are clustered in the genomes of the Aspergillus spp. fungi that produce them, and dothistromin research has already revealed intriguing similarities to the aflatoxin system. The availability of the D. septosporum genome will help us to answer long-standing questions about the evolution, regulation and biological roles of secondary metabolite gene clusters in fungi, ultimately leading to new methods of mitigating mycotoxin production.