Abstract
Yeasts of the now unused asexually typified genus Pseudozyma belong to the smut fungi (Ustilaginales) and are mostly believed to be apathogenic asexual yeasts derived from smut fungi that have lost pathogenicity on plants. However, phylogenetic studies have shown that most Pseudozyma species are phylogenetically close to smut fungi parasitic to plants, suggesting that some of the species might represent adventitious isolations of the yeast morph of otherwise plant pathogenic smut fungi. However, there are some species, such as Moesziomyces aphidis (syn. Pseudozyma aphidis) that are isolated throughout the world and sometimes are also found in clinical samples and do not have a known plant pathogenic sexual morph. In this study, it is revealed by phylogenetic investigations that isolates of the biocontrol agent Moesziomyces aphidis are interspersed with M. bullatus sexual lineages, suggesting conspecificity. This raises doubts regarding the apathogenic nature of asexual morphs previously placed in Pseudozyma, but suggests that there might also be pathogenic sexual morph counterparts for those species known only from asexual morphs. The finding that several additional species currently only known from their yeast morphs are embedded within the genus Moesziomyces, suggests that the yeast morph might play a more dominant role in this genus as compared to other genera of Ustilaginaceae. In addition, phylogenetic reconstructions demonstrated that Moesziomyces bullatus has a narrow host range and that some previously described but not widely used species names should be applied for Moesziomyces on other host genera than Echinochloa.
Highlights
Ustilaginales is the largest order within the smut fungi (Ustilaginomycetes), including species forming a blackish to brownish powdery spore mass in different organs of monocotyledonous, and exceptionally dicotyledonous plants (Vánky 2012, Begerow et al 7KH RUGHU LQFOXGHV QLQH IDPLOLHV HQFRPSDVVLQJ JHQHUD 7KH Anthracoideaceae with the occurrence on Cyperaceae and Juncaceae, and Ustilaginaceae, with few exceptions parasitic to the Poaceae, DUH WKH ODUJHVW IDPLOLHV ZLWKLQ WKH RUGHU 7KH ODWWHU FRQWDLQV the three largest smut genera, Anthracocystis, Sporisorium, and Ustilago 7KH GLIIHUHQFH EHWZHHQ WKHVH WKUHH FORVHO\ UHODWHG JHQHUD LV WKH DOPRVW FRPSOHWH ODFN RI D SODQWGHULYHG columella within sori formed by Ustilago species (Vánky 0F7DJJDUW et al 2012)
A phylogenetic hypothesis for the sampled Moesziomyces species and the cultivated yeast asexual morphs is given LQ )LJ 7KH UHVXOWV RI WKH 0LQLPXP
1,14 of Pseudozyma aphidis and the majority of M. bullatus isolates with the clade containing the type of P. rugulosa
Summary
Ustilaginales is the largest order within the smut fungi (Ustilaginomycetes), including species forming a blackish to brownish powdery spore mass in different organs of monocotyledonous, and exceptionally dicotyledonous plants (Vánky 2012, Begerow et al 7KH RUGHU LQFOXGHV QLQH IDPLOLHV HQFRPSDVVLQJ JHQHUD 7KH Anthracoideaceae with the occurrence on Cyperaceae and Juncaceae, and Ustilaginaceae, with few exceptions parasitic to the Poaceae, DUH WKH ODUJHVW IDPLOLHV ZLWKLQ WKH RUGHU 7KH ODWWHU FRQWDLQV the three largest smut genera, Anthracocystis, Sporisorium, and Ustilago 7KH GLIIHUHQFH EHWZHHQ WKHVH WKUHH FORVHO\ UHODWHG JHQHUD LV WKH DOPRVW FRPSOHWH ODFN RI D SODQWGHULYHG columella within sori formed by Ustilago species (Vánky 0F7DJJDUW et al 2012). Smut fungi of the Ustilaginales usually feature both an asexual yeast morph and a sexual morph infecting host plants in a biotrophic manner. In rare cases yeasts of the Ustilaginales could EH IRXQG WR EH DIIHFWLQJ KXPDQV 0F1HLO 3DOD]]L 7HR 7D\ 7KH HDUOLHVW FDVH RI DQ LQYDVLYH LQIHFWLRQ with an Ustilago species, possibly U. maydis, was reported in 1946 (Moore et al 1946). Spores of the Ustilaginales potentially cause pneumonias, allergic reactions, or asthma (Valverde et al 1995)
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