Secondary metabolite profiles of small-spored Alternaria support the new phylogenetic organization of the genus

Positive selection and functional diversification of transcription factor Cmr1 homologs in Alternaria

Transcription factor Cmr1 (Colletotrichum melanin regulation 1) and its homologs in several plant fungal pathogens are the regulators of the 1,8-dihydroxynaphthalene (DHN)-melanin biosynthesis pathway and have evolved functional diversification in morphology and pathogenicity. The fungal genus Alternaria comprises the group of "black fungi" that are rich in DHN-melanin in the primary cell wall and septa of the conidia. Some Alternaria species cause many economically important plant diseases worldwide. However, the evolution and function of Cmr1 homologs in Alternaria remain poorly understood. Here, we identified a total of forty-two Cmr1 homologs from forty-two Alternaria spp. and all contained one additional diverse fungal specific transcription factor motif. Phylogenetic analysis indicated the division of these homologs into five major clades and three branches. Dated phylogeny showed the A and D clades diverged latest and earliest, respectively. Molecular evolutionary analyses revealed that three amino acid sites of Cmr1 homologs in Alternaria were the targets of positive selection. Asmr1, the homolog of Cmr1 in the potato early blight pathogen, Alternaria solani was amplified and displayed the sequence conservation at the amino acid level in different A. solani isolates. Asmr1 was further confirmed to have the transcriptional activation activity and was upregulated during the early stage of potato infection. Deletion of asmr1 led to the decreased melanin content and pathogenicity, deformed conidial morphology, and responses to cell wall and fungicide stresses in A. solani. These results suggest positive selection and functional divergence have played a role in the evolution of Cmr1 homologs in Alternaria. KEY POINTS: • Cmr1 homologs were under positive selection in Alternaria species • Asmr1 is a functional transcription factor, involved in spore development, melanin biosynthesis, pathogenicity, and responses to cell wall and fungicide stresses in A. solani • Cmr1 might be used as a potential taxonomic marker of the genus Alternaria.

Alternaria sections Infectoriae and Pseudoalternaria: New genomic resources, phylogenomic analyses, and biodiversity

Species in Alternaria sections Infectoriae and Pseudoalternaria are commonly isolated from agricultural crops and a variety of other plant hosts. With the increasing appreciation that species from these two sections are often the dominant taxa recovered from important cereal crops, the need for improved understanding of their biodiversity and taxonomy has grown. Given that morphological characteristics and existing molecular markers are not sufficient for distinguishing among species, we expanded the genomic resources for these sections to support research in biosystematics and species diagnostics. Whole genome assemblies for 22 strains were generated, including the first genomes from section Infectoriae or Pseudoalternaria strains sampled from Canada, which significantly increases the number of publicly released genomes, particularly for section Pseudoalternaria. We performed comprehensive phylogenomic analyses of all available genomes (n = 39) and present the first robust phylogeny for these taxa. The segregation of the two sections was strongly supported by genomewide data, and multiple lineages were detected within each section. We then provide an overview of the biosystematics of these groups by analyzing two standard molecular markers from the largest sample of section Infectoriae and Pseudoalternaria strains studied to date. The patterns of relative diversity suggest that, in many cases, multiple species described based on minor morphological differences may actually represent different strains of the same species. A list of candidate loci for development into new informative molecular markers, which are diagnostic for sections and lineages, was created from analyses of phylogenetic signals from individual genes across the entire genome.

SRAP markers as an alternative tool for Alternaria classification

Alternaria is one of the main fungal contaminants of cereal grains worldwide with the potential to produce mycotoxins hazardous to human and animal health. Many studies have been carried out to characterize Alternaria sp.-grp. using traditional morphology or polyphasic approach, but a good correlation between morphological sp.-grp., molecular, and chemotaxonomic groups has not always been achieved. For this reason, this study aimed to investigate the usefulness of a cheaper alternative tool, SRAP markers, in identifying Alternaria sp.-grps. obtained from Argentinean barley grains and to compare it with preliminary characterization using morphological traits, phylogeny, and metabolite profiles. Fifty-three Alternaria isolates from barley grains of the main producing regions of Argentina were analyzed with four combinations of SRAP markers. The UPGMA dendrogram, based on the Simple Matching similarity coefficient, revealed three distinct groups. SRAP markers allowed the separation of Alternaria from Infectoriae sections in agreement with the results of a polyphasic approach previously made. Besides, isolates of A. arborescens sp.-grp. were clustered in a separate group from isolates of A. tenuissima and A. alternata sp.-grp., which were grouped in the same cluster. SRAP markers are a recommended tool for classifying Alternaria isolates because of its simplicity, reliability, and cost-effectiveness compared to other molecular markers.

Untargeted metabolomic analyses support the main phylogenetic groups of the common plant-associated Alternaria fungi isolated from grapevine (Vitis vinifera)

Alternaria, a cosmopolitan fungal genus is a dominant member of the grapevine (Vitis vinifera) microbiome. Several Alternaria species are known to produce a variety of secondary metabolites, which are particularly relevant to plant protection and food safety in field crops. According to previous findings, the majority of Alternaria species inhabiting grapevine belong to Alternaria sect. Alternaria. However, the phylogenetic diversity and secondary metabolite production of the distinct Alternaria species has remained unclear. In this study, our aim was to examine the genetic and metabolic diversity of endophytic Alternaria isolates associated with the above-ground tissues of the grapevine. Altogether, 270 Alternaria isolates were collected from asymptomatic leaves and grape clusters of different grapevine varieties in the Eger wine region of Hungary. After analyses of the nuclear ribosomal DNA internal transcribed spacer (ITS) and RNA polymerase second largest subunit (rpb2) sequences, 170 isolates were chosen for further analyses. Sequences of the Alternaria major allergen gene (Alt a 1), endopolygalacturonase (endoPG), OPA10-2, and KOG1058 were also included in the phylogenetic analyses. Identification of secondary metabolites and metabolite profiling of the isolates were performed using high-performance liquid chromatography (HPLC)-high-resolution tandem mass spectrometry (HR-MS/MS). The multilocus phylogeny results revealed two distinct groups in grapevine, namely A. alternata and the A. arborescens species complex (AASC). Eight main metabolites were identified in all collected Alternaria isolates, regardless of their affiliation to the species and lineages. Multivariate analyses of untargeted metabolites found no clear separations; however, a partial least squares-discriminant analysis model was able to successfully discriminate between the metabolic datasets from isolates belonging to the AASC and A. alternata. By conducting univariate analysis based on the discriminant ability of the metabolites, we also identified several features exhibiting large and significant variation between A. alternata and the AASC. The separation of these groups may suggest functional differences, which may also play a role in the functioning of the plant microbiome.

Species diversity and molecular characterization of Alternaria section Alternaria isolates collected mainly from cereal crops in Canada

Alternaria is often one on the most abundant fungal genera recovered from a wide array of plant hosts and environmental substrates. Many species within the sub-generic Alternaria section Alternaria are common plant pathogens that cause pre-harvest losses due to reduced productivity and post-harvest losses due to spoilage and contamination with mycotoxins. As certain species of Alternaria may have distinct mycotoxin profiles, and very broad host ranges, understanding the distribution of species by geography and host is critical for disease prediction, toxicological risk assessment, and guiding regulatory decisions. In two previous reports, we performed phylogenomic analyses to identify highly informative molecular markers for Alternaria section Alternaria, and validated their diagnostic ability. Here, we perform molecular characterization of 558 section Alternaria strains, collected from 64 host genera in 12 countries, using two of these section-specific loci (ASA-10 and ASA-19) along with the RNA polymerase II second largest subunit (rpb2) gene. The majority of strains (57.4%) originated from various cereal crops in Canada, which formed the main focus of our study. Phylogenetic analyses were used to classify strains into section Alternaria species/lineages, demonstrating that the most common species on Canadian cereal crops are Alternaria alternata and A. arborescens. Further population genetic analyses were consistent with A. alternata being a widely distributed species with relatively low levels of geographic isolation (i.e., Canadian isolates did not form distinct clades when compared to other regions). Our expanded sampling of A. arborescens has greatly increased the known diversity of this group, with A. arborescens isolates forming at least three distinct phylogenetic lineages. Proportionally, A. arborescens is more prevalent in Eastern Canada than in Western Canada. Sequence analyses, putative hybrids, and mating-type distributions provided some evidence for recombination events, both within and between species. There was little evidence for associations between hosts and genetic haplotypes of A. alternata or A. arborescens.

Comprehensive review on patulin and Alternaria toxins in fruit and derived products

Mycotoxins are toxic secondary metabolites produced by certain fungi, which can contaminate various food commodities, including fruits and their derived products. Patulin and Alternaria toxins are among the most commonly encountered mycotoxins in fruit and their derived products. In this review, the sources, toxicity, and regulations related to these mycotoxins, as well as their detection and mitigation strategies are widely discussed. Patulin is a mycotoxin produced mainly by the fungal genera Penicillium, Aspergillus, and Byssochlamys. Alternaria toxins, produced by fungi in the Alternaria genus, are another common group of mycotoxins found in fruits and fruit products. The most prevalent Alternaria toxins are alternariol (AOH) and alternariol monomethyl ether (AME). These mycotoxins are of concern due to their potential negative effects on human health. Ingesting fruits contaminated with these mycotoxins can cause acute and chronic health problems. Detection of patulin and Alternaria toxins in fruit and their derived products can be challenging due to their low concentrations and the complexity of the food matrices. Common analytical methods, good agricultural practices, and contamination monitoring of these mycotoxins are important for safe consumption of fruits and derived products. And Future research will continue to explore new methods for detecting and managing these mycotoxins, with the ultimate goal of ensuring the safety and quality of fruits and derived product supply.

Untargeted metabolomics screening reveals unique secondary metabolite production from Alternaria section Alternaria

Alternaria section Alternaria is comprised of many species that infect a broad diversity of important crop plants and cause post-harvest spoilage. Alternaria section Alternaria species, such as A. alternata and A. arborescens, are prolific producers of secondary metabolites that act as virulence factors of disease and are mycotoxins that accumulate in infected tissues-metabolites that can vary in their spectrum of production between individuals from the same fungal species. Untargeted metabolomics profiling of secondary metabolite production using mass spectrometry is an effective means to detect phenotypic anomalies in secondary metabolism within a species. Secondary metabolite phenotypes from 36 Alternaria section Alternaria isolates were constructed to observe frequency of production patterns. A clear and unique mass feature pattern was observed for three of the strains that were linked with the production of the dehydrocurvularin family of toxins and associated detoxification products. Examination of corresponding genomes revealed the presence of the dehydrocurvularin biosynthesis gene cluster associated with a sub-telomeric accessory region. A comparison of sequence similarity and occurrences of the dehydrocurvularin biosynthetic gene cluster within Pleosporalean fungi is presented and discussed.

Phylogenetic Analysis and Toxigenic Profile of Alternaria Species Isolated from Chickpeas (Cicer arietinum) in Argentina

Chickpeas are a very important legume due to their nutritional richness and high protein content and they are used as food for humans and as fodder for livestock. However, they are susceptible to fungal infections and mycotoxin contamination. The Alternaria genus was among the main fungi isolated from chickpea samples in Argentina. The species within this genus are able to produce several mycotoxins such as alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TA). So, the objectives of this study were to identify the Alternaria spp. found in the chickpea samples and to determine their toxigenic potential in vitro. A phylogenetic analysis of 32 Alternaria strains was carried out based on the combined sequences of the tef1, gpd, and Alt a1 genes. All Alternaria strains clustered into the section Alternaria and were identified as A. alternata and A. arborescens. Further, the toxigenic profile of each strain was determined in a ground rice–corn steep liquor medium and analysed by HPLC. Most strains were able to co-produce AOH, AME, and TA. These results indicate a potential risk for human health when consuming chickpeas since this legume could be contaminated with Alternaria and its mycotoxins, which are not yet regulated in food.

Morphological and chemical characterization of Alternaria populations from apple fruit

Alternaria is a frequent contaminant of apple fruit, causing severe economic losses. It can produce external lesions and mouldy core, characterised by a rotten area in the apple core. In the present study, morphological and chemical characterization of Alternaria from apples was performed, evaluating differences related to agricultural practices and type of disease. A low morphological diversity was observed; most of the isolates were identified as A. tenuissima sp.-grp. (95 %). A. arborescens sp.-grp. and A. gaisen sp.-grp. were present in a proportion of 1 %, and 3 % of the isolates showed intermediate characteristics between these sp.-grps. and were identified as Alternaria sp. The chemical diversity was greater; 27 secondary metabolites were produced by the apple isolates. The most frequents were altertoxin-I (85 %), altechromone A (76 %), tentoxin (69 %), and tenuazonic acid (68 %). The alternariols were produced in a lower frequency when comparing with isolates from other crops; alternariol, 58 % and alternariol monomethyl ether, 57 %. The predominant secondary metabolite profile included compounds from different chemical families, such as dibenzopyrones, tetramic acids, perylene quinones, and cyclic tetrapeptides. A wider metabolomic capacity was observed in isolates from conventional apples when compared to those from organic fruit, with the predominance of strong producers of altertoxins and alternariols. The isolates from mouldy core showed higher ability to produce metabolites from different chemical families than those from external lesions. The wide chemical diversity of the Alternaria apple population should be considered to assess the health risk associated with apple by-products.

Integrate UPLC-QE-MS/MS and Network Pharmacology to Investigate the Active Components and Action Mechanisms of Tea Cake Extract for Treating Cough

OBJECTIVE

Investigate the active components and mechanisms of tea cake extract (TCE) for treating cough.

METHODS

The components of TCE were tentatively identified by ultrahigh performance liquid chromatography coupled with Q-Exactive MS/MS (UPLC-QE-MS/MS), whose targets were obtained from databases of Swiss Target Prediction and traditional Chinese medicine systems pharmacology database and analysis platform (TCMSP). Cough-related targets were retrieved from databases of Gene cards and Online Mendelian Inheritance in Man (OMIM). After intersection targets were obtained, enrichment analysis of Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway was performed, and protein-protein interactions (PPI) network and active compound-intersection target-KEGG pathway network was constructed. Core active compounds and their targets were validated with molecular docking.

RESULTS

Total of 78 compounds were identified from TCE, including 24 flavonoids, 17 phenolic acids, 10 alkaloids, 7 organic acids, 5 triterpenes, 5 amino acids, 5 coumarins, 3 carbohydrates, 1 anthraquinone and 1 other. 347 intersection targets were obtained. The top 5 GO terms with most significant P-values were response to oxygen-containing compound, response to organic substance, response to chemical, cellular response to chemical stimulus, and regulation of biological quality. The top 5 KEGG pathways with most significant P-values were: PI3K-Akt signaling pathway, lipid and atherosclerosis, human cytomegalovirus infection, fluid shear stress and atherosclerosis, and proteoglycans in cancer. The top 5 core active compounds were: quercetin, genistein, luteolin, kaempferol and emodin. The top 5 core targets were: protein kinase B (Akt1), prostaglandin-endoperoxide synthase 2 (PTGS2), mitogen-activated protein kinase 1/3 (MAPK1/3), and phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1). The top 5 core active compounds could stably bind to their targets with LibDockScore higher than 100.

CONCLUSION

TCE plays the antitussive role by multiple components and targets. Core targets (AKT1, MAPK1, MAPK3 and PIK3R1) and core components (quercetin, genistein, luteolin and kaempferol) involved in the PI3K-Akt signaling pathway are worth more attention in subsequent validation experiments.

Genetic Structure and Triazole Antifungal Susceptibilities of Alternaria alternata from Greenhouses in Kunming, China

Alternaria alternata is an opportunistic human fungal pathogen and a ubiquitous phytopathogen capable of causing diseases to >100 agricultural crops and ornamental plants. To control plant diseases caused by A. alternata, triazole fungicides have been widely used both in open crop and vegetable fields and in indoor growth facilities such as greenhouses. At present, the effect of fungicide use on triazole resistance development in A. alternata populations is not known. Here, we isolated 237 A. alternata strains from nine greenhouses around metropolitan Kunming in Yunnan, southwest China, determined their genotypes using 10 short tandem repeat markers, and quantified their susceptibility to four triazoles (difenoconazole, tebuconazole, itraconazole, and voriconazole). Abundant allelic and genotypic diversities were detected among these A. alternata strains. Significantly, over 17% of the strains were resistant to difenoconazole, and both known and new drug-resistance mutations were found in the triazole target gene cyp51. Our findings of high-level genetic variation of A. alternata in greenhouses coupled with high-frequency fungicide resistance call for greater attention to continued monitoring and to developing alternative plant fungal disease management strategies in greenhouses. IMPORTANCE Alternaria alternata is among the most common fungi in our environments, such as indoor facilities, the soil, and outdoor air. It can cause diseases in >100 crop and ornamental plants. Furthermore, it can cause human infections. However, our understanding of its genetic diversity and antifungal susceptibility is very limited. Indeed, the critical threshold values for resistance have not been defined for most antifungal drugs in this species. Greenhouses are known to have heavy applications of agricultural fungicides. In this study, we analyzed strains of A. alternata from nine greenhouses near metropolitan Kunming in southwestern China. Our study revealed very high genetic diversity and identified strains with high MIC values against two agricultural and two medical triazole antifungals within each of the nine greenhouses. Our study calls for greater attention to this emerging threat to food security and human health.

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.

Alternaria alternata as endophyte and pathogen

Alternaria alternata is a common species of fungus frequently isolated from plants as both an endophyte and a pathogen. Although the current definition of A. alternata rests on a foundation of morphological, genetic and genomic analyses, doubts persist regarding the scope of A. alternata within the genus due to the varied symbiotic interactions and wide host range observed in these fungi. These doubts may be due in large part to the history of unstable taxonomy in Alternaria, based on limited morphological characters for species delimitation and host specificity associated with toxins encoded by genes carried on conditionally dispensable chromosomes. This review explores the history of Alternaria taxonomy, focusing in particular on the use of nutritional mode and host associations in species delimitation, with the goal of evaluating A. alternata as it currently stands based on taxonomic best practice. Given the recombination detected among isolates of A. alternata, different symbiotic associations in this species should not be considered phylogenetically informative.

(3ξ,4ξ,5ξ,6ξ,7ξ,11ξ)-3,6-Dihydroxy-8-oxo-9-eremophilene-12-oic Acid, a New Phytotoxin of Alternaria alternata ssp. tenuissima Isolates Associated with Fruit Spots on Apple (Malus × domestica Borkh.)

Alternaria sp. infections on apple (Malus × domestica Borkh.) lead to impaired fruit quality and yield losses by leaf blotches and fruit spots, caused by host-specific toxins (HSTs) of the Alternaria apple pathotype like AM-toxins. Fungal isolates were obtained during severe outbreaks on cv. Gala, Golden Delicious, and Cripps Pink^(cov)/Rosy Glow^(cov) in South Tyrol and other regions in northern Italy. The isolates were tested for pathogenicity using in vitro assays with detached apple leaves. Conidial suspensions of pathogenic isolates were shown to provoke necrotic lesions also in apple seedlings and on fruits. Detached-leaf assay-guided fractionation of the isolates' culture supernatant and a high-resolution liquid chromatography-mass spectrometry (LC-MS) analysis tentatively identified 27 known Alternaria phytotoxins and a new putative toxin, (3ξ,4ξ,5ξ,6ξ,7ξ,11ξ)-3,6-dihydroxy-8-oxo-9-eremophilene-12-oic acid (1). The constitution and the relative configuration of the ring stereocenters of 1 were elucidated by NMR spectroscopy, revealing unique structural features among Alternaria phytotoxins. Indeed, molecular analysis revealed the lack of the toxin-related genes AMT1, AMT4, and AMT14 in all isolates from the region, suggesting that Alternaria apple blotch in the area was associated with another metabolite (1).

Metabolic Profile and Mycoherbicidal Activity of Three Alternaria alternata Isolates for the Control of Convolvulus arvensis, Sonchus oleraceus, and Xanthium strumarium

Alternaria alternata isolates C1, S1, and X3 were isolated respectively from the weeds Convolvulus arvensis, Sonchus oleraceus, and Xanthium strumarium in Algiers during 2016 and identified by morphological and molecular analyses. The aim of this investigation was to chemically characterize the exometabolome of these fungi and to evaluate the myco-herbicidal potential of their culture filtrates, crude extracts, or fractions towards target weeds. Results revealed a great heterogeneity in the biochemical profiles of the exometabolome with the remarkable presence of two compounds: tenuazonic acid (TeA) and triprenyl phenol-7 (SMTP-7). To the best of our knowledge, SMTP-7—found in all the isolates—as well as 12-methoxycitromycin detected in the culture filtrate of isolate C1, have never been reported to be produced by A. alternata. Some fractions of isolates C1 and S1 showed symptoms (necrosis and chlorosis) on the detached leaves of C. arvensis and S. oleraceus, respectively with up to 100% phytotoxic effect at low concentration. In conclusion, biochemical characterization revealed great difference of C1, S1, and X3 exometabolome that is likely to explain the difference in their phytotoxic activity. Some fractions (d₁, e₁, h₁, i₁, a₂, and f₂) of isolates C1 and S1 of A. alternata caused severe necrosis and chlorosis on the injured detached leaves of C. arvensis and S. oleraceus, respectively.

Alternaria in malting barley: Characterization and distribution in relation with climatic conditions and barley cultivars

Alternaria is one of the main fungal genera affecting the quality of barley grains. In this study, a polyphasic approach was carried out to characterise the Alternaria population infecting different cultivars of barley grains from the major producing regions of Argentina in the 2014 and 2015 seasons. Its relationship with Fusarium and correlations between predominant species, barley cultivars, and climatic conditions in the growing regions were evaluated. Alternaria incidence exceeded that of Fusarium in all the barley samples and was higher in the drier season (21% in 2014 and 42% in 2015 vs. 6% and 4%, respectively). The main Alternaria species-groups identified were present in both growing seasons in similar frequencies (A. tenuissima sp.-grp., 83.4% in 2014 and 81.7% in 2015; A. infectoria sp.-grp., 11.7% in 2014 and 11.3% in 2015). The dominant Alternaria species-group isolated and identified based on morphological characteristics, DNA sequencing, and metabolite profile was A. tenuissima (72.9%), followed by A. infectoria (14.6%). An association between their frequency and field temperature was observed; A. tenuissima sp.-grp. was more frequent in northern localities, where higher temperatures were registered, while the opposite was observed for A. infectoria sp.-grp. A smaller percentage of A. arborescens sp.-grp. (5%), A. alternata sp.-grp. (3.9%) and A. vaccinii (1.4%) were also identified. Both secondary metabolite profiles and phylogenetic analysis were useful to distinguish isolates from Alternaria section Alternaria and section Infectoriae. Regarding metabolite profiles, alternariol was the most frequent compound produced by isolates of the section Alternaria. Infectopyrones and novae-zelandins were produced by most of the isolates from section Infectoriae. The barley cultivars analysed in this study did not show a particular susceptibility regarding the Alternaria population composition, except for Andreia, which presented the highest frequency of contamination with A. tenuissima sp.-grp. The rest of the cultivars, when grown in different regions, showed different proportion of the Alternaria sp.-grps., suggesting that other factors were determinant in their distribution. The results obtained in the present study will be a valuable tool for health authorities to assess the need for regulations on Alternaria mycotoxins, given the high incidence of Alternaria spp. in barley and the diversity of metabolites that might contaminate the grains.

Mycotoxin Profile and Phylogeny of Pathogenic Alternaria Species Isolated from Symptomatic Tomato Plants in Lebanon

The tomato is one of the most consumed agri-food products in Lebanon. Several fungal pathogens, including Alternaria species, can infect tomato plants during the whole growing cycle. Alternaria infections cause severe production and economic losses in field and during storage. In addition, Alternaria species represent a serious toxicological risk since they are able to produce a wide range of mycotoxins, associated with different toxic activities on human and animal health. Several Alternaria species were detected on tomatoes, among which the most important are A. solani, A. alternata, and A. arborescens. A set of 49 Alternaria strains isolated from leaves and stems of diseased tomato plants were characterised by using a polyphasic approach. All strains were included in the recently defined phylogenetic Alternaria section and grouped in three well-separated sub-clades, namely A. alternata (24 out of 49), A. arborescens (12 out of 49), and A. mali morpho-species (12 out of 49). One strain showed high genetic similarity with an A.limoniasperae reference strain. Chemical analyses showed that most of the Alternaria strains, cultured on rice, were able to produce alternariol (AOH), alternariol methyl ether (AME), altenuene (ALT) and tenuazonic acid (TA), with values up to 5634, 16,006, 5156, and 4507 mg kg⁻¹, respectively. In addition, 66% of the strains were able to co-produce simultaneously the four mycotoxins investigated. The pathogenicity test carried out on 10 Alternaria strains, representative of phylogenetic sub-clades, revealed that they were all pathogenic on tomato fruits. No significant difference among strains was observed, although A. alternata and A. arborescens strains were slightly more aggressive than A. mali morpho-species strains. This paper reports new insights on mycotoxin profiles, genetic variability, and pathogenicity of Alternaria species on tomatoes.

Characterization of Alternaria Species Associated with Heart Rot of Pomegranate Fruit

This study was aimed at identifying Alternaria species associated with heart rot disease of pomegranate fruit in southern Italy and characterizing their mycotoxigenic profile. A total of 42 Alternaria isolates were characterized. They were obtained from pomegranate fruits with symptoms of heart rot sampled in Apulia and Sicily and grouped into six distinct morphotypes based on macro- and microscopic features. According to multigene phylogenetic analysis, including internal transcribed spacer (ITS), translation elongation factor 1-α (EF-1α), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and a SCAR marker (OPA10-2), 38 isolates of morphotypes 1 to 5 were identified as Alternaria alternata, while isolates of morphotype 6, all from Sicily, clustered within the Alternaria arborescens species complex. In particular, isolates of morphotype 1, the most numerous, clustered with the ex-type isolate of A. alternata, proving to belong to A. alternata. No difference in pathogenicity on pomegranate fruits was found between isolates of A. alternata and A. arborescens and among A. alternata isolates of different morphotypes. The toxigenic profile of isolates varied greatly: in vitro, all 42 isolates produced tenuazonic acid and most of them other mycotoxins, including alternariol, alternariol monomethyl ether, altenuene and tentoxin.

Effect of Debaryomyces hansenii and the antifungal PgAFP protein on Alternaria spp. growth, toxin production, and RHO1 gene expression in a tomato-based medium

Tomato fruit is susceptible to Alternaria spp. spoilage, which poses a health risk due to their mycotoxin production. Biopreservation relies on the use of whole microorganisms or their metabolites to manage spoilage microorganisms including filamentous fungi. However, the use of treatments at fungistatic level might activate intracellular pathways, which can cause an increment in mycotoxin accumulation. The objective of this work was to evaluate the effect of two strains of Debaryomyces hansenii and the antifungal protein PgAFP at 10 and 40 μg/mL. Both growth and production of two of the most common mycotoxins (tenuazonic acid and alternariol monomethyl ether) by Alternaria tenuissima sp.-grp. and Alternaria arborescens sp.-grp. on a tomato-based matrix, were analysed at 12 °C. Additionally, the impact of these biocontrol agents on the stress-related RHO1 gene expression was assessed. All treatments reduced mycotoxin accumulation (from 27 to 92% of inhibition). Their mode of action against Alternaria spp. in tomato seems unrelated to damages to fungal cell wall integrity at the genomic level. Therefore, the two D. hansenii strains (CECT 10352 and CECT 10353) and the antifungal protein PgAFP at 10 μg/mL are suggested as biocontrol strategies in tomato fruit at postharvest stage.

Chemotaxonomic Profiling of Canadian Alternaria Populations Using High-Resolution Mass Spectrometry

Alternaria spp. occur as plant pathogens worldwide under field and storage conditions. They lead to food spoilage and also produce several classes of secondary metabolites that contaminate the food production chain. From a food safety perspective, the major challenge of assessing the risk of Alternaria contamination is the lack of a clear consensus on their species-level taxonomy. Furthermore, there are currently no reliable DNA sequencing methods to allow for differentiation of the toxigenic potential of these fungi. Our objective was to determine which species of Alternaria exist in Canada, and to describe the compounds they make. To address these issues, we performed metabolomic profiling using liquid chromatography high-resolution mass spectrometry (LC-HRMS) on 128 Canadian strains of Alternaria to determine their chemotaxonomy. The Alternaria strains were analyzed using principal component analysis (PCA) and unbiased k-means clustering to identify metabolites with significant differences (p < 0.001) between groups. Four populations or 'chemotypes' were identified within the strains studied, and several known secondary metabolites of Alternaria were identified as distinguishing metabolites, including tenuazonic acid, phomapyrones, and altenuene. Though species-level identifications could not be concluded for all groups through metabolomics alone, A. infectoria was able to be identified as a distinct population.

Biochemical control of Alternaria tenuissima infecting post-harvest fig fruit by chickpea vicilin

BACKGROUND

Alternaria tenuissima was isolated from infected fig fruit and molecularly identified by rRNA gene sequencing. The objective of the current work was to test the inhibitory effect of vicilin as a glycoprotein, isolated from chickpea, against the fungus A. tenuissima, isolated from fig fruit, in vitro and in situ, to estimate its potential action in controlling the growth of A. tenuissima in postharvest fig fruit.

RESULTS

Chickpea vicilin is a glycoprotein composed of three subunits of 135, 210, and 230 kDa. The linear growth of A. tenuissima on the solid agar medium and in liquid media (at 25 °C) was markedly reduced by 44%, 66%, 77%, and 83% and 20%, 24%, 42%, and 62%, respectively in response to vicilin applications of 0.1, 0.2, 0.3, and 0.4 g L^-1 . Chickpea vicilin (at 0.4 g L^-1 ) totally prevented fungal conidia germination during 24 h of incubation at 25 °C. Electron microscope scanning of A. tenuissima subjected to chickpea vicilin showed hyphae swelling and conidia deformation. Treating post-harvest fig fruit, artificially infected with A. tenuissima, with chickpea vicilin (0.1-0.4 g L^-1 ) restricted the disease severity to 15% against 55% in the positive control after 7 days storage.

CONCLUSION

Vicilin can be considered a potent antifungal agent that can be used in preserving fig fruit for 7-14 days with minimum disease severity. © 2020 Society of Chemical Industry.

Natural occurrence of Alternaria mycotoxins in malting barley grains in the main producing region of Argentina

BACKGROUND

Barley (Hordeum vulgare L.) is one of the most important cereals worldwide, and its quality is affected by fungal contamination such as species of the genus Alternaria. No information is available about the occurrence of Alternaria mycotoxins in Argentinean barley grains, which is of concern, because they can be transferred into malt and beer. The aim of this study was to analyze the occurrence of alternariol (AOH), alternariol monomethyl ether (AME) and tenuazonic acid (TeA) in malting barley grains from the main producing region of Argentina during the 2014 and 2015 growing seasons.

RESULTS

The most frequent mycotoxin was AOH (64%), which was detected at higher levels (712 μg kg^-1 ) compared with other studies, followed by TeA (37%, 1522 μg kg^-1 ), while AME was present in five samples in the 2015 growing season only, with a mean of 4876 μg kg^-1 . A similar frequency of mycotoxin occurrence was observed in both years (80.8 vs 85.3%), but more diverse contamination was found in 2015, which was characterized by lower accumulated precipitation. Nevertheless, AOH was more frequently found in 2014 than in 2015 (80.8 and 47.1% respectively). A negative correlation between AOH concentration and temperature was observed. The susceptibility of different barley varieties to mycotoxin accumulation varied with the mycotoxin, geographical location and meteorological conditions.

CONCLUSION

The results obtained in the present work represent a tool for risk assessment of exposition to these mycotoxins and could be used by food safety authorities to determine the need for their regulation. Furthermore, the establishment of a hazard analysis and critical control point (HACCP) system to minimize fungal and mycotoxin contamination in barley from farm to processing could be apply to ensure food safety. © 2019 Society of Chemical Industry.

Alternaria species associated to wheat black point identified through a multilocus sequence approach

Black point is one of the most important wheat disease and its incidence is increasing worldwide due to climate change too. Among the fungal genera that can cause black point, Alternaria is one of the predominant genus, often associated with mycotoxin contamination. The correct identification is the baseline for prevention and control of the disease. Taxonomy of the genus Alternaria is not completely clear yet, since its species can be differentiated for few morphological traits and, in some cases, also molecular phylogeny is not very effective in establishing species boundaries. In this study, one-hundred sixty-four strains, isolated from wheat kernels affected by black point sampled worldwide, were analyzed in order to assess their identity. Sequences of elongation factor, β-tubulin, glyceraldehyde-3-phosphate dehydrogenase and allergen alt-a1 genes were used to identify the variability of this population and their phylogenetic relationships. Isolates were grouped in two main clades: the Alternaria section, including A. alternata, A. tenuissima and A. arborescens species, and the Infectoriae section, that includes the two species A. infectoria and A. triticina. Comparison of isolates according with their area of isolation did not show a correlation between phylogeny and geographic origin. Indeed, the isolates grouped on the base of only their phylogenetic relationship. Due to the data arisen by our study, we strongly recommend a multilocus sequence approach to define Alternaria species, based on common genes and procedures to be unanimously shared by scientific community dealing with Alternaria genus. Moreover, we suggest that A. alternata, A. tenuissima, A. turkisafria and A. limoniasperae species would be merged in the defined species A. alternata. Finally we recommend to consider a taxonomic re-evaluation of the Infectoriae section that, for the morphology, sexuality, genetic and mycotoxin profile of the species included, could be defined as different fungal genus from Alternaria.