Evolutionary patterns of host type and chasmothecial appendage morphology in obligate plant parasites belonging to Cystotheceae (powdery mildew, Erysiphaceae)

Phylogeny and taxonomy of the genera of Erysiphaceae, part 7: Phyllactinieae

The seventh part of this series devoted to the phylogeny and taxonomy of powdery mildews presents the phylogeny and taxonomy of species assigned to the genera Leveillula, Phyllactinia, Pleochaeta, and Queirozia (Erysiphaceae tribe Phyllactinieae). Phylogenetic trees based on multiple loci (ITS+28S, CAM, GADPH, GS, IGS, RPB2, and TUB) are presented. All species with available sequence data are included. The present analyses aim at providing a reference for analyses of powdery mildews of tribe Phyllactinieae. A special focus is on the generic distinction at the base of tribe Phyllactinieae and between Leveillula and Phyllactinia. The inclusion of a larger number of phylogenetically basal Phyllactinia spp. and multiple loci allowed a better insight into the phylogeny of tribe Phyllactinieae and confirmed that Leveillula spp. are nested within the Phyllactinia clade. As a consequence, Leveillula is reduced to synonymy with Phyllactinia. Additionally, Queirozia was found to be nested within the Pleochaeta clade, and as such we have reduced Queirozia to synonymy with Pleochaeta. Multiple species have been sequenced for the first time, in particular multiple North American species. Erysiphe betulae, E. orbicularis, E. polychaeta, E. saxaouli, Phyllactinia antarctica, Ph. broussonetiae-kaempferi, Ph. hamamelidis, Ph. kakicola, Ph. pyri-serotinae, Ph. salmonii, Ph. zanthoxylicola, Uncinula lynchii, and U. shiraiana are epitypified. The new species Ph. amelanchieris, sp. nov. Ph. fraxini-pennsylvanicae, sp. nov. and Ph. oemleriae, sp. nov. are described, and the new combinations Phyllactinia buddlejae, Ph. cleomes, Ph. cylindrospora, Ph. farinosa, Ph. golovinii, Ph. guilanensis, Ph. jaczewskii, Ph. lactucae-seriolae, Ph. lactucarum, Ph. lanugiosa, Ph. lappae, Ph. mindii, Ph. oxalidicola, Ph. picridis, Ph. rubiae, Ph. saxaoulii, Ph. taurica, Ph. thevenotiae, Ph. ulmi (comb. et stat. nov.), Ph. verbasci, Ph. wissadulae, and Pleochaeta erysiphoides are introduced. Furthermore, Phyllactinia sect. Basiphyllactinia, sect. nov. Phyllactinia sect. Leveillula, comb. et stat. nov. and Pleochaeta sect. Ovulariopsis, comb. et stat. nov. are presented.

Evolutionary dependence of host type and chasmothecial appendage morphology in obligate plant parasites belonging to Erysipheae (powdery mildew, Erysiphaceae)

Evolutionary relationships between the morphological and ecological traits of fungi are poorly understood. The appendages of chasmothecia, which are sexual reproductive organs of Erysiphaceae, are considered to play a crucial role in the overwintering strategies of these fungi on host plants. Previous studies suggested that both the host type and appendage morphology evolved at the same nodes and transitioned from complex appendages on deciduous hosts to simple appendages on herb/evergreen hosts. However, the evolutionary dependence between host type and appendage morphology remains unproven owing to the limited species data used in analyses. To elucidate the evolutionary relationship between host type and appendage morphology, we used phylogenetic comparative methods (PCMs) to investigate the state transition, ancestral state, evolutionary dependence, and contingent evolution within Erysipheae, the largest and most diverse tribe in Erysiphaceae. Our PCMs, based on a comprehensive data set of Erysipheae, revealed that the most ancestral states were deciduous host types and complex appendages. From these ancestral states, convergent evolution toward the herb/evergreen host types and simple appendages occurred multiple times at the same nodes. For the first time in Erysiphaceae, we detected an evolutionary dependence between host type and appendage morphology. This is one of the few examples in which evolutionary dependence between host phenology and morphological traits in plant-parasitic fungi was demonstrated using PCMs. Appendage simplification on herb/evergreen hosts and complications on deciduous hosts can be reasonably explained by the functional advantages of each appendage type in different overwintering strategies. These expected appendage functions can explain approximately 90% of host type and appendage morphology combinations observed in the analyzed taxa. However, our results also highlighted the occurrence of evolutionary shifts that deviate from the expected advantages of each appendage morphology. These seemingly irrational shifts might be interpretable from the flexibility of overwintering strategies and quantification of appendage functions.