Seiridium species on Acacia mearnsii in South Africa and Australia.
Aylward, J.*1,2, Roets, F.2, Wingfield, B. D.1, Wingfield, M. J.1
1 Department of Biochemistry, Genetics and Microbiology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Private Bag X20 Hatfield, 0028, South Africa
2 Department of Conservation Ecology and Entomology, Stellenbosch University, Private Bag X1 Matieland, 7602, South Africa
Seiridium is a genus of Sordariomycete fungi in the Order Xylariales, primarily known for its members that cause cypress canker on Cupressaceae trees. Most species have been reported from native gymnosperms or angiosperms in Australia, China, Europe and South Africa. A recent survey of Seiridium species in the culture collection (CMW) of the Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, revealed several unidentified Seiridium isolates collected approximately 40 years ago on Acacia mearnsii trees in eastern South Africa and southeastern Australia. The aim of this study was to identify these isolates and to assess their pathogenicity on A. mearnsii. Regions of the Btub, EF1a and RPB2 genes were sequenced to construct a maximum likelihood phylogeny, revealing three well-supported monophyletic clades. Two clades corresponded to South African and Australian origins, while the third included two South African isolates and an Australian species isolated from Eucalyptus cladocalyx. Whole-genome sequences were generated for isolates in each clade and comparisons were made to determine average pairwise nucleotide identity among all genomes. Based on whole-genome and phylogenetic analyses, we conclude that the isolates represent S. kartense that was originally described from E. cladocalyx on Kangaroo Island. The pathogenicity trial showed that four of the South African isolates were not pathogenic to A. mearnsii, with no obvious lesions developing around the sites of inoculation after seven weeks. The cultures considered in this study have been conserved for many decades, making possible this study and the first report of a Seiridium species on A. mearnsii. Importantly, it emphasises the relevance of living culture collections and the role that they can play in future studies and where new technologies emerge to study the biology of fungi.
Keywords: culture collection, cypress canker, genomes, pathogenicity, taxonomy
