Submitted to: Mycological Progress
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/3/2013
Publication Date: 6/22/2013
Citation: Lawrence, D., Pryor, B., Dugan, F.M., Pryor, B. 2013. Characterization of Alternaria isolates from the infectoria species-group and a new taxon from Arrhenatherum, Pseudoalternaria arrhenatheria sp. nov. Mycological Progress. DOI: 10.1007/s11557-013-0910-x. Interpretive Summary: The Alternaria infectoria species-group is one of several groups of species in the fungal genus Alternaria. The conidia (asexual spores) of this group are morphologically very similar to those in other species-groups, such as the Alternaria alternata species-group. However, species-groups designated on the basis of morphology are not always congruent with species-groups defined on the basis of phylogeny. However, the infectoria species-group is coherent (and separated from other species-groups) by the branching patterns of its conidiophores (spore-producing hyphal branches), by phylogeny, and on the basis of production of secondary compounds (e.g., mycotoxins). Alternaria is a genus containing many important plant pathogens and is of importance for allergenicity and sometimes in clinical settings. This study facilitates identification of species (named or otherwise) within the infectoria species-group and illustrates the phylogenetic separation of the infectoria species-group from other species placed in Alternaria.
Technical Abstract: The infectoria species-group within the genus Alternaria was originally conceived by Simmons in 1993 and was based upon common morphological characteristics that included the development of conidial chains with primary, secondary, and tertiary branching resulting in substantial three-dimensional complexity. These characters can overlap to varying degrees with numerous taxa in another Alternaria group, the alternata species-group, making species-group differentiation difficult. However, members of the infectoria species-group are also distinguished from other small-spored Alternaria species based upon colony characteristics that typically include white or nearly white floccose colonies on DRYES medium and clumps of sporulation islands on low sugar media such as V8 agar and weak PDA. In addition, the infectoria species-group contains the only known representatives of Alternaria that are known to produce teleomorphs, whereas the members of the alternata species-group are strictly asexual. In this study, an assemblage of isolates recovered from varied hosts within a single geographic region, the west coast of the United States, were examined based upon additional morphological characters and compared to previously described members of the infectoria species-group. Members of the infectoria species-group typically produce arachnoid vegetative hyphae with multiple primary conidiophores, whereas other small-spored Alternaria species produce primary conidiophores predominately directly from the agar surface. Additionally, molecular phylogenetic analyses resolved the infectoria species-group (teleomorph Lewia) as distinctly nested amongst other sexual taxa in Allewia (Embellisia anamorph) and Macrospora (Nimbya anamorph) and phylogenetically distant to asexual lineages of Alternaria. A new genus is proposed, Pseudoalternaria gen. nov.; a new taxon is described, Pseudoalternaria arrhenatheria sp. nov.; and a second taxon is reclassified, Pseudoalternaria rosae nov. comb. This work also suggests that all remaining anamorphic taxa in the infectoria species-group be placed within the new genus Pseudoalternaria.