Species delimitation for Neonectria coccinea group including the causal agents of beech bark disease in Asia, Europe, and North America.
Neonectria coccinea has historically been known as a serious pathogen of beech trees in North America and Europe. Phylogenetic relationships of this species and its relatives have been determined. Neonectria faginata, previously referred to as Neo. coccinea var. faginata has been delimited from Neo. coccinea sensu stricto and Neo. punicea. Five additional lineages supported by relatively high phylogenetic values are allied with Neo. coccinea and its relatives. Until now, these lineages have not been recognized as species because no significant morphological differences among them were found. Although each phylogenetic species appeared to be unique in host specificity and geography, relatively few specimens of these species existed. We re-evaluated these species using newly obtained specimens and isolates from Asia, Europe, and North America. Based on sequences of multiple loci, specifically act, ITS, LSU, rpb1, tef1 and tub, our results indicate that these isolates represent four phylogenetic species, Neo. coccinea, Neo. faginata, Neo. microconidia, and Neo. punicea. In our phylogeny, each species is well supported by high BI PP, MP BP, and ML BP values. The single-locus analyses of ITS and LSU did not correlate with our species recognition criteria. Based on morphology, phylogeny, host specificity and geographical traits, these four species are conclusively delimited. Each of them is re-described and illustrated. Epitype specimens for Sphaeria coccinea and Neonectria coccinea var. faginata are designated. Because no type specimen of Neo. punicea was found, this name is neotypified. Within Neo. coccinea, Neo. microconidia, and Neo. punicea, some sublineages were supported by high phylogenetic values. In the future these may warrant recognition as distinct species.