Cronartium rust (Pucciniales, Cronartiaceae): species delineation, diversity and host alternation

Cronartium species (Basidiomycota, Pucciniales, Melampsorineae) infect two or five-needle pines, resulting in considerable economic losses and ecological damage. Many species are considered of quarantine importance, however, precise identification is challenging due to the poorly resolved generic boundaries of Cronartium and other members in Melampsorineae, as well as species limits within the genus Cronartium. In this study, species delimitation was carried out based on morphological examination and multi-locus phylogenetic assessment using sequences of rDNA SSU-ITS-LSU regions and CO3 gene. Twenty-six species including seven new species (C. castaneae, C. mongolicum, C. murrayanae, C. myricae, C. peridiatum, C. qinlingense, C. ribistaedae), and one new combination (C. floridanum) are recognized. Cronartium arizonicum, C. comandrae, C. comptoniae, C. occidentale, and C. pyriforme are epitypified to stabilize the use of names for taxonomy and quarantine significance. In addition, 18 species were revealed for their previously unknown life cycles.