Mycosphaerella

Mycosphaerella is a genus of ascomycota. With more than 10,000 species, it is the largest genus of plant pathogen fungi. The following introduction about the fungal genus Mycosphaerella is copied (with permission) from the dissertation of Dr. W. Quaedvlieg (named: Re-evaluating Mycosphaerella andallied genera), publicly available at http://dspace.library.uu.nl/handle/1874/308485 Species belonging to the fungal genus Mycosphaerella (1884) (Capnodiales, Dothideomycetes) have evolved as endophytes, saprotrophs and symbionts, but mostly Mycosphaerellaspecies are foliicolous plant pathogens which are the cause of significant economical losses inboth temperate and tropical crops worldwide. The generic concept of Mycosphaerella is based on the type species of the genus, M. punctiformis, which was introduced130 years ago in order to describe small loculoascomycetes with few distinct morphologicaltraits. Species belonging to Mycosphaerella were characterised as having pseudothecial ascomata that can be immersed or superficial, embedded in host tissue or erumpent, having ostiolar periphyses, but lacking interascal tissue at maturity. Ascospores are hyaline, but in somecases slightly pigmented and predominantly 1-septate, although taxa with 3-septate ascospores have been recorded. This description appears to be quite distinctive, but is in fact verybroad and actually lead to 120 years of confusion in which the generic name Mycosphaerellawas being used as a dumping ground for small loculoascomycetes with few distinct morphological traits. In the 19th and 20th centuries, thousands of species and infrasprecific taxa weredescribed in the genus Sphaerella, only to have the entire genus and about 1000 additionalspecies redescribed into the genus Mycosphaerella at the end of the 20th century. The identification of Mycosphaerella species by morphological means is extremely difficult asthese taxa produce very small fruiting structures with highly conserved morphologies, tendingto grow and sporulate poorly in culture and for over 120 years, identification wasbased on morphology alone. These identification difficulties are amplified by the fact that upto six different species can inhabit the same lesion as either a primary or secondary pathogen, making even host-specific species difficult to identify. Theintroduction of affordable sequencing technology during the first decade of the 21st centuryallowed for much more accurate species delimitation and phylogenetic elucidation, leading tothe conclusion that the broad taxonomic description of the genus Mycosphaerella and a lack ofclear morphological features led to many Mycosphaerella and mycosphaerella-like species being misidentified. Because the classic taxonomic description of Mycosphaerella is broad and includesso many mycosphaerella-like species, the traditional generic concept of Mycosphaerella willhereafter be referred to as Mycosphaerella sensu lato (s. lat.) in order to avoid confusion. Currently more than 3 000 species and close to 10 000 names are associated with Mycosphaerella s. lat., but work by Verkley et al. (2004) revealed that the genusMycosphaerella s. str. (based on M. punctiformis) was in fact limited to species with Ramulariaasexual morphs. Research by Braun (1990, 1998) showed that there are only about 500 Ramularia species known from literature, leaving the majority of mycosphaerella-like species thatwill need to be reclassified into taxonomically correct genera and families. Since the advent ofmass sequencing technology, 39 taxonomically correct genera have already been confirmedas belonging to the Mycosphaerellaceae via molecular means: (Amycosphaerella, Neopseudocercospora, Ramularia, Caryophylloseptoria, Neoseptoria, Ramulispora, Cercospora, Pallidocercospora, Ruptoseptoria, Cercosporella, Paracercospora, Scolecostigmina, Colletogloeum, Paramycosphaerella, Septoria, Cytostagonospora, Passalora*, Sonderhenia, Distocercospora, Periconiella, Sphaerulina, Dothistroma, Phaeophleospora, Stenella, Lecanosticta, Phloeospora, Stromatoseptoria, Microcyclosporella, Polyphialoseptoria, Trochophora, Neodeightoniella, Polythrincium, Xenomycosphaerella, Neomycosphaerella, Pseudocercospora, Zasmidium, Neopenidiella, Pseudocercosporella* and Zymoseptoria) Although at least 25 more genera with postulated Mycosphaerellaceae affinity have yet to be confirmed.The current generic and family concepts of both Mycosphaerella s. str., the Mycosphaerellaceae and the Teratosphaeriaceae have evolved indirectly from the work of Crous (1998), whoused culture and asexual morphological characteristics to show that Mycosphaerella s. lat.was in fact polyphyletic, suggesting that it should be subdivided into natural genera as definedby its asexual morphs. In contrast to these findings, the first sequence-based phylogenetic trees published for Mycosphaerella s. lat. (based mainly on ITS nrDNA sequence data), suggested that Mycosphaerella was monophyletic. However, as more sequence data of Mycosphaerella spp. became available (especially of loci such as the 28S nrDNA), the view of Mycosphaerella s. lat. as beingmonophyletic has gradually shifted and there is now ample evidence that Mycosphaerella inits broadest sense is polyphyletic. Since this discovery was made, the originalconserved generic concept of Mycosphaerella s. lat. has been replaced with the concept thatthe mycosphaerella-like morphology has evolved multiple times and that these taxa in factcluster in diverse families such as the Cladosporiaceae, Dissoconiaceae, Mycosphaerellaceae and Teratosphaeriaceae. As such, the name Mycosphaerella should be limited to species with Ramularia sexual forms, but the name Ramularia actually predates the name Mycosphaerella, so the name Ramularia has preference over Mycosphaerella, and will be placed on the list of protected names.