Taxonomy and Phylogeny of the Genus Mycosphaerella and Its Anamorphs

Fungal Diversity Reviews, Critiques and New Ideas Taxonomy and phylogeny of the genus Mycosphaerella and its anamorphs Crous, P.W. CBS-KNAW Fungal Biodiversity Centre, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands Crous, P.W. (2009). Taxonomy and phylogeny of the genus Mycosphaerella and its anamorphs. Fungal Diversity 38: 1- 24. Historically plant pathogenic species of Mycosphaerella have been regarded as host-specific, though this hypothesys has proven difficult to test largely due to the inavailability of fungal cultures. During the course of the past 20 years a concerted effort has been made to collect these fungi, and devise methods to cultivate them. Based on subsequent DNA sequence analyses the majority of these species were revealed to be host-specific, though some were not, suggesting that no general rule can be applied. Furthermore, analysis of recent molecular data revealed Mycosphaerella to be poly- and paraphyletic. Teleomorph morphology was shown to be too narrowly defined in some cases, and again too widely in others. Mycosphaerella and Teratosphaeria as presently circumscribed represent numerous different genera, many of which can be recognised based on the morphology of their 30 odd associated anamorph genera. Although Mycosphaerella is generally accepted to represent one of the largest genera of ascomycetous fungi, these data suggest that this is incorrect, and that Mycosphaerella should be restricted to taxa linked to Ramularia anamorphs. Furthermore, other anamorph form genera with Mycosphaerella-like teleomorphs appear to represent genera in their own right. Key words: Anamorphs, Capnodiales, Mycosphaerella, polyphyletic, Teratosphaeria, systematics Article Information Received 9 June 2009 Accepted 6 July 2009 Published online 1 October 2009 *Corresponding author: Crous, P.W.; e-mail: [email protected]. Introduction although some are associated with stem cankers (Cortinas et al., 2006), fruit lesions Species of Mycosphaerella have adapted (Pretorius et al., 2003) or blemishes, spots and in various ways to different ecosystems, and specks (Batzer et al., 2008). Damage is usually vary from being saprobic, plant pathogenic to due to defoliation, which reduces the photo- hyperparasitic (de Hoog et al., 1991; Goodwin synthetic capacity of the crop, leading to et al., 2001; Jackson et al., 2004; Arzanlou et growth loss. Some species, such as M. citri, al., 2007b). Mycosphaerella spp. are among the affect both leaves and fruits. Others such as M. most common and destructive plant pathogens fijiensis, infect banana leaves, thereby reducing known, causing considerable economic losses the photosynthetic capacity of the crop, and on a wide variety of host plants worldwide, also induce physiological changes resulting in including economically important crops such premature ripening of fruit (Carlier et al., 2000; as banana, cereals, sugar beet, strawberry, Marin et al., 2003). soybean, citrus, eucalypts, acacia, pines and The first generic description for Myco- many others (Farr et al., 1995; Crous and sphaerella (1884) was that of Sphaerella Braun, 2003). Plant pathogenic Myco- (1882). Saccardo placed all species of Sphaeria sphaerella species are mainly foliicolous, with presumably 1-septate, hyaline ascospores 1 in Sphaerella. The genus Sphaerella was, (Braun et al., 2003; Crous et al., 2007a; however, already in use for green algae, and Schubert et al., 2007a,b; Zalar et al., 2007), for thus all these taxa had to be placed in which the family Davidiellaceae was Mycosphaerella (Aptroot, 2006), which is established (Schoch et al., 2006). based on M. punctiformis (Verkley et al., 2004). Section Caterva: cylindrical asci and Despite the hyaline, 1-septate ascospores irregularly arranged, thin-walled, often reported in the type by Persoon (1794), most medium-sized ascospores, that are rarely authors at the beginning of the 19th century constricted at the septum and inequilateral, worked without microscopes, and thus what with more or less pointed ends. Asteromella they described as a Sphaeria or Sphaerella spermatial forms are typical. Representative species, literally meant a ‘spherical’ fruiting species: the common polyphagous M. subra- body (Aptroot, 2006). Soon it became standard dians. to also describe collections from different hosts Section Longispora: cylindrical asci with as new species, which later led to many taxa aggregated, thin-walled, long and slender being reduced to synonymy (Von Arx, 1949; ascospores that are rarely constricted at the Barr, 1972; Tomilin, 1979; Corlett, 1991; septum and mostly equilateral, long but slender Aptroot, 2006). In the recent revision of ascospores, characteristically with rounded Mycosphaerella names, Aptroot (2006) treated upper and pointed lower ends. Anamorphs: close to 10,000 taxa, recognising around 3,000 Phloeospora or Septoria s. lat. Representative species. species: M. eryngii (with short spores), M. In her treatment of North American taxa, latebrosa and M. populi (with longer spores). Barr (1972) recognised two subgenera, Eu- The phylogenetic position of Sphaerulina, Mycosphaerella and Didymellina (including which differs by having additional ascospore the section Cymadothea), and 10 sections. The septa, still needs to be resolved. sub-genera were separated on the basis of the Section Fusispora: pyriform asci and shape of their asci and anamorphs, and the irregularly arranged, thin-walled ascospores sections based on ascospore shape, and/or that are rarely constricted at the septum and parasitic or saprobic habit. Von Arx (1983) mostly equilateral, fusiform, pointed asco- found the subdivision unsatisfactory, because spores. Anamorphs have not been proven. the characters were inordinately divergent. Representative species: the common M. lineolata on Poaceae. The sections of Barr were refined by Crous Section Plaga: (incl. Section Macula) et al. (2000) as follows incorporates endophytic species sporulating on leaf spots, many of which are described as Section Mycosphaerella: cylindrical asci plant pathogens. This section is characterised and mostly uniseriate, thin-walled, often small by obovoid to ellipsoidal or cylindrical asci, ascospores that are constricted at the septum small to medium sized ascopores, fusiform to and inequilateral, with rounded upper ends. obovoid with rounded ends. Many species have Anamorphs: typically Ramularia with Astero- been described in this section, the majority of mella spermatial states. Representative species: which originate from warm-temperate and the common polyphagous M. punctiformis. tropical areas. Anamorphs include Kirramyces, Section Tassiana: pyriform asci and Passalora, Phaeophleospora, Pseudocerco- irregularly arranged, thick-walled ascospores spora, Pseudocercosporella, Sonderhenia and that are often large and constricted at the Stenella. Several representative species are septum and nearly equilateral, relatively broad listed by Crous (1998) on Eucalyptus. with rounded ends, containing irregular lumina. Section Cymadothea: This section is Anamorph: Cladosporium s. str. Representa- now accepted as the genus Polytrincium tive species: the common polyphagous species (Cymadothea teleomorph) (Simon et al., 2009). Davidiella tassiana. Further research supported Cymadothea has superficial ascomata situated the decision of David (1997) to place on a stroma of pseudoparenchymatal cells, and Heteroconium anamorphs in Cladosporium, ascospores that can become pale brown with while section Tassiana was elevated to generic age. The Polytrincium anamorph is quite level as Davidiella (Cladosporium anamorphs) 2 Fungal Diversity unique, forming fascicles with conidiogenous separate genera within Mycosphaerella, though loci arranged along the one side of the initial DNA phylogenies based on ITS conidiogenous cells, with slightly darkened sequence data refuted this (Crous et al., 2000; scars. Representative species: the genus is Goodwin et al., 2001; but see below). Although monotypic, with P. trifolii occurring on Sutton and Hennebert (1994) suggested that Trifolium. different anamorph conidiogenous events and Von Arx (1949) proposed separating conidiomatal types could prove useful in species with separate ascomata immersed grouping species at some subgeneric level, the within the host tissue, and those with ascomata presence of synanamorphs (Crous et al., occurring in pseudoparenchymatous stromata. 2007a,c), and general plasticity observed in This idea certainly has merit, but too few taxa conidiogenesis and conidiomatal structure in the latter category have been subjected to when studied in culture, suggests that these DNA analyses to fully test this proposal. The characters should be used with caution. original hypothesis of separating species with Barr (1996) placed two species occurring pigmented ascospores into Phaeosphaerella, on pine needles in a new genus, Eruptio while retaining those with hyaline ascospores (Lecanosticta and Dothistroma anamorphs) in Mycosphaerella, should also be rein- based on their elongate, erumpent ascostromata vestigated. This separation was also followed that open via schizogenously formed ostioles. by Tomilin (1979). However, Müller and von The taxa presently accommodated in Eruptio Arx (1962) found that the type species of are, however, not congeneric, and this genus Phaeosphaerella, P. maculosa was identical to will have to be evaluated further in future Venturia macularis. A new generic name studies. would thus have to be introduced for species Although Sphaerulina was established to

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