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Applying population genomics to understand the genomic basis of speciation, pathogenicity and host specialization in Ceratocystis fimbriata sensu lato

Tuan Duong: Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria

<div><em>Ceratocystis fimbriata sensu stricto</em> was first descibed in 1890 as the causal agent of sweet potato black rot in the USA. More recently, several cryptic species related to <em>C. fimbrirata s.s.</em> have been described as major pathogens of various tree crops including acacia, eucalypts, mango and pomegranate in Asia, Africa and South America. Studies using phylogenetic analyses, population genetic markers and mating have shown that these species are closely related and in some cases inter-fertile. Consequently, their species boundaries are a source of disagreement and collectively, we treat them as members of <em>C. fimbriata sensu lato</em>. Several studies have revealed that some of these species are host specific. However, nothing is known regarding the genetic basis of their host specificity or pathogenicity. We sequenced the genomes of a relatively large number of <em>C. fimbriata s.l.</em> isolates collected from five different hosts on which these fungi are pathogenic. Population genomic analyses revealed that isolates were clustered based on hosts from which they were isolated. Additionally, genomes of these fungi displayed the “two-speed” genome signatures, similar to those known in other plant pathogenic fungi and oomycetes. We are currently identifying and characterizing genes residing in genomic regions with accelerated evolution. The results will provide insights into the genetics of host specialization and speciation in these important species of <em>Ceratocystis</em> <em>s.l</em>.</div>