Genome size estimates for six rust (Pucciniales) species

Rust fungi (Basidiomycota, Pucciniales), one of the largest groups of phytopathogenic organisms, are characterised by host specialisation, biotrophy, complex life cycles and enlarged genomes. In this work we have used flow cytometry to determine the genome size of six rust species, Melampsora pulcherrima, Puccinia behenis, P. cichorii, P. pimpinellae, P. vincae and Uromyces dianthi, the causal agents of rust on Mercurialis annua, Silene latifolia, Cichorium intybus, Pimpinella villosa, Vinca major and Dianthus caryophyllus, respectively. With results ranging between 182.1 and 566.4 Mbp/1C, this study has contributed to the knowledge of genome sizes in the order Pucciniales, reinforcing this group as the one with the largest average genome size among fungi, with 335.6 Mbp/1C. By comparing genome sizes and their variability across the fungal kingdom, this study has contributed for understanding the patterns of genome size distribution along the fungal phylogeny, suggesting links between biological specificities and genome sizes. In particular, genome sizes of rust fungi vary greatly within genera, but also differ sharply from other non- Pucciniales orders in the Pucciniomycotina, suggesting that genome size variation may be an active element shaping the evolution of rust fungi.