Revision of Alternaria sections Pseudoulocladium and Ulocladioides: Assessment of species boundaries, determination of mating-type loci, and identification of Russian strains.

Abstract

Alternaria is a large genus within Pleosporaceae and consists of fungi that have up to recently been considered to be 15 separate genera, including Ulocladium. The majority of Ulocladium species after incorporation into Alternaria were placed in three sections: Ulocladioides, Pseudoulocladium, and Ulocladium. In this study, phylogeny of 26 reference strains of 22 species and 20 Russian Ulocladium-like isolates was recovered. The partial actin gene (act), Alternaria major allergen (alta1), calmodulin (cal), glyceraldehyde-3-phosphate dehydrogenase (gapdh), RNA polymerase II second largest subunit (rpb2), and translation elongation factor 1-α (tef1) were sequenced for Russian isolates. All these fungi were examined using multilocus phylogenetic analysis according to the genealogical concordance phylogenetic species recognition (GCPSR) principle and the coalescent-based model Poisson tree processes (PTP, mPTP) and evaluated for the presence of recombination. All strains were combined into two clades that corresponded to the Pseudoulocladium and Ulocladioides sections. The Pseudoulocladium clade included four reference strains and nine local isolates and considered to be a single species, whereas the Ulocladioides section comprises 11 species, instead of 17 names previously adopted. Nine species were abolished by joining four other species. Species A. atra and A. multiformis were combined into the single species A. atra. Five species, A. brassicae-pekinensis, A. consortialis, A. cucurbitae, A. obovoidea, and A. terricola, were united in the species A. consortialis. Alternaria heterospora and A. subcucurbitae were combined into one species, A. subcucurbitae. Alternaria aspera, A. chartarum, A. concatenata, and A. septospora were combined into a single species, A. chartarum. Also, amplification with two different primer sets was performed to define mating-type locus 1 (MAT1) idiomorph. All studied isolates were heterothallic, contradicting some prior studies. Twenty Russian Ulocladium-like isolates were assigned to five species of two sections, A. atra, A. cantlous, A. chartarum, A. consortialis, and A. subcucurbitae. Species A. cantlous and A. subcucurbitae were found in Russia for the first time.