Association Mapping of Beech Bark Disease in American Beech

The American Beech tree (Fagus grandifolia Ehrh.), native to eastern North America, has significant ecological importance and provides high quality hardwood for wood products. This species is currently susceptible to beech bark disease (BBD) and it is facing considerable rates of mortality in North America. The disease occurs from an interaction between woolly beech scale insect (Cryptococcus fagisuga) and one of two species of the fungus Nectria (N. coccinea or N. galligena).

The project aims to determine genetic architecture of disease resistance and describe patterns of genetic and phenotypic variation. The question of interest in our study would be are the alleles or genotypes at a genetic marker associated with disease status? We will use statistical methods such as unconditional logistic regression or Fisher’s exact test to access associations between SNPs and phenotypes. Here we will apply approach to associate variation of 512 unrelated individuals with ~18K high confidence SNPs.

The final EST sequence database originated from two transcriptome assemblies (http://ecosystems.psu.edu/research/centers/schatz/research) was used as SNPs source for genotyping in association study. To gain insight into the molecular mechanisms underlying disease resistance in F. grandifolia, RNA samples were sequenced by using Roche 454 short reads sequencing platform when RNA was isolated from both disease-resistance and disease-susceptible.

As the major outcome of this study, we expect to identify candidate genes for resistance that contain polymorphisms reported to be associated with Beech Bark Disease (BBD).

Key words: association genetics, American beech tree, disease resistance