Mycosphaerella Alocasiae

''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 W. Quaedvlieg (named: Re-evaluating ''Mycosphaerella'' and allied genera).

Species belonging to the fungal genus ''Mycosphaerella'' (1884) (''Capnodiales'', ''Dothideomycetes'') have evolved as endophytes, saprotrophs and symbionts, but mostly ''Mycosphaerella'' species are foliicolous plant pathogens which are the cause of significant economical losses in both temperate and tropical crops worldwide. The generic concept of Mycosphaerella is based on the type species of the genus, ''M. punctiformis'', which was introduced \130 years ago in order to describe small loculoascomycetes with few distinct morphological traits. 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 some cases 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 very broad and actually lead to 120 years of confusion in which the generic name ''Mycosphaerella'' was 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 were described in the genus ''Sphaerella'', only to have the entire genus and about 1000 additional species redescribed into the genus ''Mycosphaerella'' at the end of the 20th century.

The identification of ''Mycosphaerella'' species by morphological means is extremely difficult as these taxa produce very small fruiting structures with highly conserved morphologies, tending to grow and sporulate poorly in culture and for over 120 years, identification was based on morphology alone. These identification difficulties are amplified by the fact that up to six different species can inhabit the same lesion as either a primary or secondary pathogen, making even host-specific species difficult to identify. The introduction of affordable sequencing technology during the first decade of the 21st century
allowed for much more accurate species delimitation and phylogenetic elucidation, leading to the conclusion that the broad taxonomic description of the genus ''Mycosphaerella'' and a lack of clear morphological features led to many ''Mycosphaerella'' and mycosphaerella-like species being misidentified. Because the classic taxonomic description of ''Mycosphaerella'' is broad and includes so many mycosphaerella-like species, the traditional generic concept of ''Mycosphaerella'' will hereafter 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 genus ''Mycosphaerella'' s. str. (based on ''M. punctiformis'') was in fact limited to species with ''Ramularia'' asexual 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 that will need to be reclassified into taxonomically correct genera and families. Since the advent of mass sequencing technology, 39 taxonomically correct genera have already been confirmed as 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'')
* The genera ''Passalora'' and ''Pseudocercosporella'' are known to be paraphyletic and will be treated separately in the near future.

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), who used 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 defined
by 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 being monophyletic has gradually shifted and there is now ample evidence that ''Mycosphaerella'' in its broadest sense is polyphyletic. Since this discovery was made, the original conserved generic concept of ''Mycosphaerella'' s. lat. has been replaced with the concept that the mycosphaerella-like morphology has evolved multiple times and that these taxa in fact cluster 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.

Mating type

Three closely related ''Mycosphaerella'' species, '' M. fijiensis'', '' M. musicola'' and '' M. eumusae'' cause a destructive disease of bananas. Each of these three species is heterothallic, that is, matings can only occur between individuals of different mating type. Although the mating type DNA sequences of the three species appear to have arisen from a common ancestral sequence, there also has been considerable evolutionary divergence between them.Arzanlou M, Crous PW, Zwiers LH. Evolutionary dynamics of mating-type loci of Mycosphaerella spp. occurring on banana. Eukaryot Cell. 2010 Jan;9(1):164-72. doi: 10.1128/EC.00194-09. Epub 2009 Nov 13. PMID:19915079

References

{{Taxonbar, from=Q3869075

Mycosphaerellaceae genera