Distinction of Alternaria Sect. Pseudoalternaria Strains among Other Alternaria Fungi from Cereals.

Species of the genus Alternaria are ubiquitous and frequently isolated from various plants, including crops. There are two phylogenetically and morphologically close Alternaria sections: the relatively well-known Infectoriae and the rarely mentioned Pseudoalternaria. Currently, the latter includes at least seven species that are less studied and sometimes misidentified. To perform precise identification, two primers (APsF and APsR) were designed and a sect. Pseudoalternaria-specific PCR method was developed. Thirty-five Russian A. infectoria-like strains were then examined. Five strains were found to be the members of the sect. Pseudoalternaria. Additionally, specificity of the previously developed primer set (Ain3F and Ain4R) was checked. It was found to be highly specific for sect. Infectoriae and did not amplify sect. Pseudoalternaria DNA. Identification of strains of the sect. Pseudoalternaria was supported and refined by phylogenetic reconstruction based on analysis of two loci, the glyceraldehyde-3-phosphate dehydrogenase gene (gpd), and the plasma membrane ATPase gene (ATP). These fungi belonged to Alternaria kordkuyana and A. rosae, which were the first detection of those taxa for the Eastern Europe. Alternaria kordkuyana was isolated from cereal seeds and eleuthero leaves. Alternaria rosae was obtained from oat seed. All strains of sect. Pseudoalternaria were not able to produce alternariol mycotoxin, as well as the majority of A. sect. Infectoriae strains.

Diaporthe species infecting sunflower (Helianthus annuus) in Russia, with the description of two new species.

Phomopsis stem canker is economically important sunflower disease that caused by multiple Diaporthe species. Recent investigations resulted in the resolution that there are at least 13 Diaporthe species that can infect sunflower. A comprehensive analysis of the biodiversity and geographic distribution of Diaporthe species in Russia, particularly those that infect sunflower, has not been undertaken. For this study, 16 Diaporthe isolates were obtained from samples of stem canker and visually healthy seeds of Helianthus annuus from northwestern, central European, southern European Russia, North Caucasus, and the Urals in 2016-2019. The aim of this study was to identify these Diaporthe isolates based on morphology and sequence analyses of the nuclear ribosomal internal transcribed spacer (ITS) region, partial calmodulin (cal), DNA-lyase (apn2), histone H3 (his3), translation elongation factor-1α gene (tef1), and ß-tubulin (tub2) genes. The phylogenetic reconstruction revealed well-supported monophyletic clades corresponding to six Diaporthe species: D. eres, D. gulyae, D. helianthi, and D. phaseolorum. Two new species were described: Diaporthe monetii sp. nov. and Diaporthe vangoghii sp. nov. The isolates of D. gulyae and D. phaseolorum collected represent the first records of these species in Russia.

Analysis of Host-Specific Differentiation of Puccinia striiformis in the South and North-West of the European Part of Russia.

Yellow (stripe) rust, caused by Puccinia striiformis Westend. (Pst), is a major disease of cereals worldwide. We studied Pst virulence phenotypes on Triticum aestivum, Triticum durum, and triticale in three geographically distant regions of the European part of Russia (Dagestan and Krasnodar in North Caucasus, and Northwest) with different climate and environmental conditions. Based on the set of twenty differential lines, a relatively high level of population diversity was determined with 67 different Pst pathotypes identified among 141 isolates. Only seven pathotypes were shared by at least two hosts or occurred in the different regions. No significant differentiation was found between regional Pst collections of pathotypes either from T. aestivum or from T. durum. A set of Pst pathotypes from triticale was subdivided into two groups. One of them was indistinguishable from most durum and common wheat pathotypes, whereas the second group differed greatly from all other pathotypes. All sampled Pst isolates were avirulent on lines with Yr5, Yr10, Yr15, and Yr24 genes. Significant variation in virulence frequency among all Pst collections was observed on lines containing Yr1, Yr3, Yr17, Yr27, and YrSp genes and cvs Strubes Dickkopf, Carstens V, and Nord Desprez. Relationships between Russian regional collections of Pst from wheat did not conform to those for P. triticina.

Natural Occurrence of Alternaria Fungi and Associated Mycotoxins in Small-Grain Cereals from The Urals and West Siberia Regions of Russia.

Alternaria fungi dominate the grain microbiota in many regions of the world; therefore, the detection of species that are able to produce mycotoxins has received much attention. A total of 178 grain samples of wheat, barley and oat obtained from the Urals and West Siberia regions of Russia in 2017-2019 were included in the study. Grain contamination with Alternaria fungi belonging to sections Alternaria and Infectoriae was analysed using qPCR with specific primers. The occurrence of four mycotoxins produced by Alternaria, AOH, AME, TEN, and TeA, was defined by HPLC-MS/MS. Alternaria DNA was found in all analysed grain samples. The prevalence of DNA of Alternaria sect. Alternaria fungi (range 53 × 10-4-21,731 × 10-4 pg/ng) over the DNA of Alternaria sect. Infectoriae (range 11 × 10-4‒4237 × 10-4 pg/ng) in the grain samples was revealed. Sixty-two percent of grain samples were contaminated by at least two Alternaria mycotoxins. The combination of TEN and TeA was found most often. Eight percent of grain samples were contaminated by all four mycotoxins, and only 3% of samples were free from the analysed secondary toxic metabolites. The amounts varied in a range of 2-53 µg/kg for AOH, 3-56 µg/kg for AME, 3-131 µg/kg for TEN and 9-15,000 µg/kg for TeA. To our knowledge, a new global maximum level of natural contamination of wheat grain with TeA was detected. A positive correlation between the amount of DNA from Alternaria sect. Alternaria and TeA was observed. The significant effects of cereal species and geographic origin of samples on the amounts of DNA and mycotoxins of Alternaria spp. in grain were revealed. Barley was the most heavily contaminated with fungi belonging to both sections. The content of AOH in oat grain was, on average, higher than that found in wheat and barley. The content of TEN in the grain of barley was lower than that in wheat and similar to that in oat. The content of TeA did not depend on the cereal crop. The effect of weather conditions (summer temperature and rainfall) on the final fungal and mycotoxin contamination of grain was discussed. The frequent co-occurrence of different Alternaria fungi and their mycotoxins in grain indicates the need for further studies investigating this issue.

The sections of Alternaria: formalizing species-group concepts.

The systematics of Alternaria and allied genera traditionally has been based on the characteristics of conidia and the sporulation apparatus. This emphasis on morphology in the reconstruction of organismal relationships has resulted in taxonomic uncertainty and flux for a number of taxa in Alternaria and the related genera Stemphylium, Embellisia, Nimbya and Ulocladium. The present study used a molecular phylogenetic approach for systematic resolution and incorporated extensive taxon sampling (n = 176 species) representing 10 genera and analyses of 10 protein-coding loci. Phylogenetic analyses based on five of these genes revealed eight distinct asexual lineages of Alternaria that cluster as the sister group to the asexual paraphyletic genus Ulocladium, while taxa with known teleomorphs currently circumscribed as Alternaria (the infectoria species-group) cluster among genera that also have representatives with known teleomorphs. This work proposes to elevate the eight well supported asexual lineages of Alternaria to the taxonomic rank of section. Evolutionary relationships among Alternaria and closely related genera are discussed.