Phylogeny and taxonomy of Golovinomyces orontii revisited

Abstract

Golovinomyces orontii is a common plurivorous powdery mildew species with wide host range and worldwide distribution, usually occurring as asexual morph. Ascomata (chasmothecia) are rarely formed on most hosts. Phylogenetic analyses based on rDNA ITS and 28S rDNA data of a wide range of powdery mildew collections of G. orontii s. lat. suggested a high degree of genetic heterogeneity of this species, which is undoubtedly not monophyletic. This study revealed that sequences retrieved from numerous collections referred to as G. orontii (s. lat.) split into three distinct main clusters, previously classified as groups 1 to 3. These groups have been genetically and morphologically analyzed, circumscribed, and named. One cluster (group 2), including a sequence retrieved from powdery mildew on the type host of Erysiphe orontii, Misopates orontium, constitutes G. orontii s. str. G. tabaci comb. nov. ( E. tabaci) is introduced for the second cluster in group 1 that is genetically and morphologically clearly distinct from G. orontii s. str. The third assemblage of sequences (group 3) comprises powdery mildews on hosts of the composite tribe Cichorieae, including Cichorium and Lactuca spp., and a wide range of hosts belonging to various other plant families for which the name G. bolayi sp. nov. is proposed. Euoidium longipes and Euoidium lycopersici, two additional powdery mildew species on solanaceous hosts, are briefly discussed and, based on previous phylogenetic analyses, reallocated to Golovinomyces. Oidium lactucae-debilis on Ixeris japonica in Asia is tentatively reduced to synonymy with G. sonchicola, i.e., it does not pertain to the G. orontii s. lat. complex. G. orontii s. lat. on Vinca spp. (Apocynaceae), mostly known as asexual morph, represents a separate species only distantly related to G. orontii s. str., which is described herein as Golovinomyces vincae sp. nov. Some re-examined collections on Vinca major from Germany misidentified as G. orontii turned out to belong to Ramularia vincae and represent first records of this species for Germany. Golovinomyces spadiceus is a further plurivorous Golovinomyces species discussed in this work, which, however, does not belong to the G. orontii complex.