Key to the major groups of plant parasitic microfungi in Europe

(Schlüssel für die Großgruppen pflanzenparasitischer Kleinpilze in Europa)

by M. Scholler & G. Hagedorn

This is a preliminary key to the major groups of parasitic fungi in Europe. It is not designed to be used world-wide, where additional taxa may occur with other characteristics. The groups recognized here are not necessarily phylogenetic taxa and do not follow the newest taxonomical knowledge. Rather they are groups as commonly recognized by plant pathologists. The arrangement follows the publication of Brandenburger 1985, which forms a major part of the current GLOPP data. We added, however, the order Exobasidiales which is not represented in Brandenburger's book.

This key only contains features which can be observed by the naked eye or by using a hand lens or light microscope. Some mycological experience, however, will be required to correctly identify the major groups. We plan to supplement this complete key with a document containing short descriptions and illustrations that help you to recognize the most important pathogen groups. Further, we already provide a first draft of a literature list that may be useful to continue the identification within each major group of plant parasitic microfungi.

1.		Obligate intracellular parasites, often in roots	Plasmodiophoromycota
1.	*	Extracellular parasites (obligate or facultative)	2
2.		Mycelium mainly aseptate (rarely with secondary septa) and/or mycelium scarcely developed	3
2.	*	Mycelium well developed and septate	9
3.		Mycelium scarcely developed, fungus mostly pigmented, orange to red, motile spores with one flagellum only, and often thick-walled resting spores. Commonly parasites of water or wetland plants.	Chytridiomycota
3.	*	Mycelium colorless to slightly grayish, violet or light brown, spores formed in sporangia releasing spores with two flagellae (motile) or without flagellae (not motile), formation of thick-walled resting spores within host tissue, obligate or facultative parasites.	Oomycota, 6
4.		No formation of sexual (meiotic) spores, although asexual (mitotic) exogenous spores are produced by most species. Mycelium pigmented or colorless	form division Deuteromycota 9 (= anamorphic fungi)
4.	*	Formation of sexual spores (meiospores), often in fruit-bodies. Often forming asexual spores (mitospores) as well	5
5.		Meiospores (ascospores) endogenous, formed in asci	Ascomycota, 12
5.	*	Meiospores (basidiospores) exogenous, borne on septate phragmobasidia or non-septate holobasidia	Basidiomycota, 22

Subkey Oomycota

6.		Sporangiophores branched (in the genus Basidiophora branches are reduced to several short "sterigmata" on top) or in chains, with or without motile spores, on stems and leaves of dicots	(Peronosporales) 7
6.	*	Sporangiophores unbranched or sparsely differentiated and not in chains	8
7.		Obligate parasites on land plants (especially Brassicaceae), sporangiophores in chains, forming white sori	Albuginaceae: Albugo ("white rusts")
7.	*	Obligate parasites on land plants, sporangiophores branched and not in chains, often on the underside of leaves	Peronosporaceae ("downy mildews")
8.		Hyphae ca. 20 µm diam., increasing with age (up to 150 µm), on aquatic plants	Saprolegniaceae ("water molds")
8.	*	Hyphae ca. 6-10 µm diam.	Pythiaceae

Subkey Deuteromycota (anamorphic fungi, Fungi Imperfecti)

9.		No formation of spores	form division Agonomycetales, Mycelia sterilia
9.	*	Formation of colorless or pigmented exogenous spores (conidia)	10
10.		Conidia not in fruit-bodies; conidia produced directly on the mycelium, on separate conidiogenous cells, or on distinct conidiophores that may be separate, in clusters, or in tightly packed groups	form class Hyphomycetes
10.	*	Conidia formed in well-defined asexual fruit-bodies, often facultative parasites	(form class Coelomycetes) 11
11.		Conidia typically produced in saucer-shaped fruit-bodies covered by the host epidermis (acervuli)	Melanconiales
11.	*	Conidia typically produced in more or less roundish, flask-shaped fruit-bodies (pycnidia)	Sphaeropsidales

Subkey Ascomycota

12.		Formation of true mycelium and (budding) pseudomycelium, no ascomata, ascospores fusiform with appendix	Hemiascomycetes: Endomycetales (Nematospora)
12.	*	Not with this combination of features	13
13.		Ascomata not developed, ascospores budding	14
13.	*	Ascomata developed, ascospores germinating with a germ tube, not budding	15
14.		Forming thick-walled ascogenous resting spores subepidermal, usually gall-forming, often on Apiaceae (Parsley family)	Hemiascomycetes: Protomycetales
14.	*	No formation of thick-walled resting spores, forming a layer of asci on substrate surface (leaves, fruits). Often forming conspicuous galls or witches brooms	Hemiascomycetes: Taphrinales
15.		Formation of conspicuous white mycelium with unbranched conidiophores, often on the upper leaf surface, ascomata small (less than 500 µm), black, globose and cleistothecia-like (without any opening, but with asci arranged in a hymenium), ascomata with appendices	Pyrenomycetes: Erysiphales ("powdery mildews")
15.	*	Anamorph and ascomata not as above	16
16.		Asci bitunicate, ascomata variable in shape, initials form a stroma with internal loculi in which the asci are formed, ascomata dark brown	(Loculascomycetes) 17
16.	*	Ascomata different, asci unitunicate or, when bitunicate, forming more or less cup-shaped fruitbodies (apothecia)	18
17.		Ascomata without premature opening	Dothideinae
17.	*	Ascomata with premature opening	Pseudosphaeriineae
18.		Asci inoperculate, with apical pore, forming no apothecia	19
18.	*	Asci operculate or inoperculate, forming apothecia	(Discomycetes) 20
19.		Mycelium black, hyphae thick-walled with hyphopodia and setae, fruit-bodies black, globose, without ostiolum	Pyrenomycetes: Meliolales (Meliola)
19.	*	Ascomata typical perithecia with a pore-, papilla- or neck-like opening (ostiolum)	Pyrenomycetes: Sphaeriales
20.		Asci operculate or splitting above an apical ring, forming apothecia	Pezizales
20.	*	Asci inoperculate, with apical pore, forming apothecia	21
21.		Hymenium in a superficial apothecium, not immersed in plant tissue	Helotiales
21.	*	Hymenium of apothecium developed in host tissue, becoming exposed by splitting of a dark covering layer	Phacidiales (= Rhytismatales)

Subkey Basidiomycota

22.		Septate dikaryotic mycelium without clamp connections, formation of phragmobasidia only, basidiospores germinating with germ tube forming hyphae, forming small fruiting structures, ranging from yellow-orange to rust-red to darkbrown in color mainly on stems and leaves, on herbaceous and woody vascular plants and on ferns. Spores variable in shape. Thin-walled spores usually one-celled borne in chains or on stalks, thick-walled spores one-to multi-celled (but mostly two-celled) and often stalked. Most species with more than one sorus and spore type, respectively.	Uredinales ("rust fungi")
22.	*	Dikaryotic mycelium with clamp connections, basidiospores budding, monokaryotic yeast stage saprotrophic	23
23.		Sori often locally in specific plant structures like flowers, anthers, seeds, roots, stem nodes, leaf margins, etc., in brown to black masses. Some species form (mainly pale) spores in the plant matrix causing pale to white spots, formation of phragmo- and holobasidia, mainly on herbaceous angiosperms, not on ferns	Ustilaginales ("smut fungi")
23.	*	Formation of a usually whitish layer of "naked" holobasidia on leaf surface, forming galls, infected leaves often turning red, on Ericaceae (Heath family)	Exobasidiales