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GWAS-based analysis of quantitative traits in Ceratocystis albifundus

Magriet van der Nest: Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria

<div><em>Ceratocystis albifundus</em> is an important pathogen of commercially propagated <em>Acacia mearnsii</em> and <em>Protea cynaroides</em> in South Africa. It also infects wounds on a wide range of native African tree species without causing disease. Previous work has shown that <em>C. albifundus</em> exhibits quantitative traits (i.e. growth rate, laccase activity and virulence) likely involved in its ability to infect and cause disease on its plant hosts. In this study, we identified polymorphisms and genes associated with these quantitative traits by employing a genome-wide association study (GWAS). For this purpose, 36 genetically diverse <em>C. albifundus</em> isolates, originating from a wide range of host species and geographic regions, were used. The isolates were phenotyped using growth rate measurements on potato dextrose agar medium, alpha-napthol-based laccase assays, and pathogenicity tests on <em>A. mearnsii</em> seedlings. To determine their genotypes, isolates were subjected to low-coverage genome sequencing using Ion Torrent technology. These sequences were mapped to a reference genome, which was generated with the PacBio and Illumina sequencing platforms. Correlation analysis between genotypes and the respective phenotypes allowed identification of genomic regions that are significantly associated with the three quantitative traits examined<em>.</em> Future characterization of these genomic regions will reveal their role in growth rate, laccase activity, virulence and the overall biology of <em>C. albifundus</em>.</div>