Abstract Detail

Mycological Section

Sakalidis, Monique [1], Feau, Nicolas [1], Dhillon, Braham [1], Hamelin, Richard C. [1].

A tree pathogen- presence, persistence and expansion in a domesticated world.

During tree domestication, hybrid tree species are created and broadly deployed. But commercial planting practices and strategic breeding for traits that are desirable for commercial production (fast growth, high fiber content) often inadvertently shape the evolution of pathogens that exist on these trees. In some cases this domestication of wild pathogens alongside their host generates new diseases that can have devastating consequences. The Dothideomycete fungus, Mycosphaerella populorum Thompson (anamorph: Sphaerulina musiva Peck) is an endemic fungus that occurs naturally on wild poplar in north-eastern and north-central North America where it causes innocuous leaf infections. Increased reports of this pathogen, including an ability to colonise and cause cankers in woody tissue coincided with the expansion of the poplar industry. This pathogen was most recently reported in hybrid poplar in British Columbia (BC) in 2006 and in Alberta (AB) in 2009. A recent comparison between this pathogen and its sister species M. populicola identified candidate pathogenicity genes that appear to be involved in canker formation on poplar. In order to manage disease spread, prevent further incursions and identify genes involved in plant attack we decoded the genomes of 83 strains of the pathogen. We found shared genes involved in adaptation across all populations and regional adaptation generating local geographic populations. These geographic populations also displayed significant difference in virulence profiles on different genotypes of Poplar trichocarpa. This indicates that we cannot necessarily predict the level of resistance of a poplar genotype by infection with a single fungal strain. It also suggests that M. populorum may have the capacity to evolve new virulence to overcome host resistance. The new populations recently identified in BC and AB revealed strikingly different genomic profiles. The BC population is one of the most genetically diverse populations identified, most likely due to the introduction of multiple genotypes from different sources. Contrasting with the BC population, the AB population has a strikingly low diversity and appears to have evolved clonally. Modelling using genomic profiles shows that the pathogen originated in the US, a centre of diversity and has repeatedly spread or been introduced into Canada. The most likely vector enabling these repeated introductions is symptomless poplar material exchanged for commercial plantations or breeding programs. To prevent further spread and assist in traceback analyses we have developed a “SNPchip” that can assign new reports to source populations.

1 - University of British Columbia, Department of Forest and Conservation Sciences, 2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada

Keywords:
Population Genomics
Fungi
Phenotype
Pathogenicity
poplar
canker
Septoria musiva
Mycosphaerella populorum 
Sphaerulina musiva .

Presentation Type: Oral Paper:Papers for Sections
Session: 64
Location: Salon 1/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 11:30 AM
Number: 64006
Abstract ID:1021
Candidate for Awards:None