Pacific Northwest Fungi Volume 1, Number 12, Pages 1-27 Published December 5, 2006 Synopsis of genera of Erysiphales (powdery mildew fungi) occurring in the Pacific Northwest Dean A. Glawe Department of Plant Pathology, Washington State University, and College of Forest Resources, Box 352100, University of Washington, Seattle, WA 98195. Glawe, D. A. 2006. Synopsis of genera of Erysiphales (powdery mildew fungi) occurring in the Pacific Northwest. Pacific Northwest Fungi 1(12): 1-27. DOI: 10.2509/pnwf.2006.001.012 Corresponding author: Dean A. Glawe, [email protected] Accepted for publication December 1, 2006. Copyright © 2006 Pacific Northwest Fungi Project. All rights reserved. Abstract: The Erysiphales (powdery mildew fungi) are Ascomycetes of major economic significance. Recent taxonomic research, mostly in Asia and Europe, has produced major changes in genus concepts complicating identification of powdery mildew fungi and communication about the diseases they cause. This paper provides a summary of genus concepts applicable to powdery mildew fungi known in the Pacific Northwest, as well as dichotomous keys based on both anamorphic and teleomorphic features, and brief summaries of diagnostic features. Salient morphological features are illustrated with photographs made from recent collections from the region. The following genera are included: Arthrocladiella, Blumeria, Erysiphe, Golovinomyces, Leveillula, Neoerysiphe, Phyllactinia, Podosphaera, and Sawadaea. Consistent with modern systems of classification, Microsphaera, Uncinula, and Uncinuliella are subsumed within the modern concept of Erysiphe, and Sphaerotheca species are included in Podosphaera. 2 Glawe. Genera of Erysiphales in the Pacific Northwest.. Pacific Northwest Fungi 1(12): 1-27. Key Words: Erysiphales, powdery mildew, Arthrocladiella, Blumeria, Erysiphe, Golovinomyces, Leveillula, Microsphaera, Neoerysiphe, Phyllactinia, Podosphaera, Sawadaea, Sphaerotheca, Uncinula, Uncinuliella, biodiversity, fungal taxonomy, fungal morphology. Introduction subulate, or mycelioid. Chasmothecia with mycelioid appendages typically overwinter The Erysiphales (powdery mildew fungi) are on the substrate on which they formed. Ascomycetes obligately parasitic on Chasmothecia with other kinds of angiosperms (Braun, 1987). They are appendages typically dehisce from the site among the most economically important of origin and disperse to new locations plant pathogenic fungi and because of their before overwintering. Appendages can play significance there is a long history of roles in detaching chasmothecia from research on their taxonomy and biology. In substrates, providing aerodynamic qualities North America, taxonomic research on enhancing dispersal, or attaching them to Erysiphales has lagged behind other parts new substrates (Webster, 1979). After of the world (Braun et al., 2002). overwintering, asci protrude or are Consequently it can be difficult to determine discharged through ruptured chasmothecial the modern names to apply to Erysiphales walls to eject ascospores which then infect occurring on this continent. new host material (Salmon, 1907). This paper is intended to be a practical aid Ascospores germinate to form hyphae that to determining the genus names to apply to generally produce differentiated outgrowths Erysiphales in the North American Pacific termed appressoria. Appressoria in turn Northwest. The paper briefly summarizes form infection structures to penetrate walls and illustrates diagnostic features for of epidermal cells, forming haustoria within modern genera applicable to these fungi. them. In most taxa, hyphae primarily are Diagnostic features are illustrated with formed superficially on host tissue, although photographs made from recent collections in some, perhaps most notably species of of Pacific Northwest species. Phyllactinia and Leveillula, extensive amounts of hyphae grow within host tissue. Morphological features used in Conidiophores are formed from superficial distinguishing genera of Erysiphales mycelia, or in taxa with internal mycelia can arise inside host tissue and emerge through Determination of Erysiphales is based on a stomata to produce conidia. Multiple variety of morphological structures conidia are produced in succession from produced throughout their life cycles (Braun, each conidiophore. Two basic kinds of 1987; Braun et al., 2002). Erysiphales are conidiophores are recognized (Braun et al., pleomorphic fungi, with life cycles typically 2002): in one kind, conidia mature singly, involving both sexual (teleomorphic) and dehiscing upon maturation at which time a asexual (anamorphic) states. Erysiphales new conidium develops (Fig. 10); in the ascocarps, termed chasmothecia, usually other kind, a series of conidia mature more range from about 80 µmto 450 µm in gradually, resulting in a chain of conidia diameter and vary from nearly spherical to exhibiting increasing maturity distal to the more or less hemispherical, rarely turbinate. conidiogenous cell (Fig. 8). In the absence Chasmothecia form various kinds of of disturbance, conidia formed singly may appendages including ones that can be accrue in false chains (Fig. 29). In most acicular, dichotomously-branched, uncinate, taxa, conidia produced from a single Glawe. Genera of Erysiphales in the Pacific Northwest.. Pacific Northwest Fungi 1(12): 1-27. 3 conidiophore are morphologically similar. [Fig. 32], or with both macroconidia and However, in Leveillula two kinds of conidia microconidia [Figs. 65, 66]). Teleomorph are produced. The first-formed conidium, features include: number of asci contained sometimes termed the primary or lanceolate in a single ascocarp (one ascus [Fig. 56] or conidium, exhibits a narrowed apex. The multiple asci [Fig. 14]); and ascocarp other kind of conidium, termed the appendages.At the genus level significant secondary or cylindrical conidium, is formed distinctions are made between two groups following production of the primary conidium of taxa: those with both acicular and lacks the narrowed apex. In species of appendages and penicillate cells (Figs. 42- Sawadaea both macroconidia and 44) and those that produce mycelioid (Fig. microconidia are formed, distinguished on 11), dichotomously branched (Fig. 15), or the basis of relative size. An additional uncinate appendages (Fig. 17). In some conidial feature with taxonomic significance cases, such as Arthrocladiella, host is the fibrosin body. Fibrosin bodies are information can also be useful in refractive, cytoplasmic structures that occur determining the genus of powdery mildew. within conidia and exhibit varied shapes Arthrocladiella has been found only on the including comma’s, cones, or rods (Braun et solanaceous genus Lycium (Braun, 1987). al., 2002). However, most genera include species with varied host ranges. Life cycles may lack either the teleomorph or the anamorph, and this feature may vary Genus names used for Erysiphales within the same species. In regions with climates including cold winters the entire life The nomenclatural history of Erysiphales cycle, involving both teleomorphs and dates to 1753 when the first binomial for a anamorphs, commonly operates. In regions powdery mildew was published by Linnaeus with mild winters, such as the coastal (Braun, 1987). Far from being a mere Pacific Northwest, teleomorphs can be historical curiosity, early work continues to difficult to find, suggesting that they may be influential. Léveillé’s (1851) genus occur either infrequently or perhaps have concepts for Erysiphales marked a been lost (e.g., Glawe, 2003). At least one significant advance over previous species of Erysiphales, Parauncinula approaches and continue to influence septata (E. S. Salmon) S. Takam. & U. classification systems. Names applied to Braun, appears to form only the teleomorph North American species of Erysiphales (Takamatsu et al., 2005), but it has not been traditionally followed an approach that can found in the Pacific Northwest. be traced to work of Burrill (Burrill and Earle, 1887; Ellis and Everhart, 1892) and Salmon In practice, a rather small number of (1900). A conspicuous feature of those morphologic features distinguishable with taxonomic systems is the emphasis on light microscopy are sufficient to determine teleomorphic features to the point that genera of Erysiphales. With respect to anamorphic features are nearly ignored. species known to occur in the Pacific Interestingly enough, Burrill’s treatment of Northwest, examples of taxonomically Erysiphales in Ellis and Everhart’s (1892) useful features of the anamorph include North American Pyrenomycetes includes morphology of: appressoria (usually either little information on anamorphs, while the nipple-shaped [Fig. 1] or lobed [Fig. 9]); accompanying drawings by F. W. Anderson conidiophore foot cells (with inflated base clearly illustrate features such as whether [Fig. 7] or cylindrical base [Fig. 37]); conidia formed either singly or in chains— conidiophores (forming conidia singly [Fig. characteristics emphasized heavily in 10]or in chains [Fig. 53]); fibrosin bodies modern approaches. Anamorphic (present [Fig. 54] or absent [Fig. 4]) and characters in most named species remain to conidia (monomorphic [Fig. 3], or dimorphic be described (Braun et al., 2002). 4 Glawe. Genera of Erysiphales in the Pacific Northwest.. Pacific Northwest Fungi 1(12): 1-27. Shaw’s (1973a, b) compilation of fungi in Erysiphales: Erysiphe, Microsphaera, the Pacific Northwest reflected taxonomic Uncinula, Podosphaera, Sphaerotheca,