Revealing the diversity of Jojoba-associated fungi using amplicon metagenome approach and assessing the in vitro biocontrol activity of its cultivable community.

Jojoba shrubs are wild plants cultivated in arid and semiarid lands and characterized by tolerance to drought, salinity, and high temperatures. Fungi associated with such plants may be attributed to the tolerance of host plants against biotic stress in addition to the promotion of plant growth. Previous studies showed the importance of jojoba as jojoba oil in the agricultural field; however, no prior study discussed the role of jojoba-associated fungi (JAF) in reflecting plant health and the possibility of using JAF in biocontrol. Here, the culture-independent and culture-dependent approaches were performed to study the diversity of the jojoba-associated fungi. Then, the cultivable fungi were evaluated for in-vitro antagonistic activity and in vitro plant growth promotion assays. The metagenome analysis revealed the existence of four fungal phyla: Ascomycota, Aphelidiomycota, Basidiomycota, and Mortierellomycota. The phylum Ascomycota was the most common and had the highest relative abundance in soil, root, branch, and fruit samples (59.7%, 50.7%, 49.8%, and 52.4%, respectively). Alternaria was the most abundant genus in aboveground tissues: branch (43.7%) and fruit (32.1%), while the genus Discosia had the highest abundance in the underground samples: soil (24%) and root (30.7%). For the culture-dependent method, a total of 14 fungi were isolated, identified, and screened for their chitinolytic and antagonist activity against three phytopathogenic fungi (Fusarium oxysporum, Alternaria alternata and Rhizoctonia solani) as well as their in vitro plant growth promotion (PGP) activity. Based on ITS sequence analysis, the selected potent isolates were identified as Aspergillus stellatusEJ-JFF3, Aspergillus flavus EJ-JFF4, Stilbocrea sp. EJ-JLF1, Fusarium solani EJ-JRF3, and Amesia atrobrunneaEJ-JSF4. The endophyte strain A. flavus EJ-JFF4 exhibited the highest chitinolytic activity (9 Enzyme Index) and antagonistic potential against Fusarium oxysporum, Alternaria alternata, and Rhizoctonia solani phytopathogens with inhibitory percentages of 72, 70, and 80 respectively. Also, A. flavus EJ-JFF4 had significant multiple PGP properties, including siderophore production (69.3%), phosphate solubilization (95.4 µg ml-1). The greatest production of Indol-3-Acetic Acid was belonged to A. atrobrunnea EJ-JSF4 (114.5 µg ml-1). The analysis of FUNGuild revealed the abundance of symbiotrophs over other trophic modes, and the guild of endophytes was commonly assigned in all samples. For the first time, this study uncovered fungal diversity associated with jojoba plants using a culture-independent approach and in-vitro assessed the roles of cultivable fungal strains in promoting plant growth and biocontrol. The present study indicated the significance of jojoba shrubs as a potential source of diverse fungi with high biocontrol and PGP activities.

Molecular Mechanism of Resistance to Alternaria alternata Apple Pathotype in Apple by Alternative Splicing of Transcription Factor MdMYB6-like.

As a fruit tree with great economic value, apple is widely cultivated in China. However, apple leaf spot disease causes significant damage to apple quality and economic value. In our study, we found that MdMYB6-like is a transcription factor without auto-activation activity and with three alternative spliced variants. Among them, MdMYB6-like-ß responded positively to the pathogen infection. Overexpression of MdMYB6-like-ß increased the lignin content of leaves and improved the pathogenic resistance of apple flesh callus. In addition, all three alternative spliced variants of MdMYB6-like could bind to the promoter of MdBGLU H. Therefore, we believe that MdMYB6-like plays an important role in the infection process of the pathogen and lays a solid foundation for breeding disease-resistant cultivars of apple in the future.

In silico approaches for the identification of potential allergens among hypothetical proteins from Alternaria alternata and its functional annotation.

Direct exposure to the fungal species Alternaria alternata is a major risk factor for the development of asthma, allergic rhinitis, and inflammation. As of November 23rd 2020, the NCBI protein database showed 11,227 proteins from A. alternata genome as hypothetical proteins (HPs). Allergens are the main causative of several life-threatening diseases, especially in fungal infections. Therefore, the main aim of the study is to identify the potentially allergenic inducible proteins from the HPs in A. alternata and their associated functional assignment for the complete understanding of the complex biological systems at the molecular level. AlgPred and Structural Database of Allergenic Proteins (SDAP) were used for the prediction of potential allergens from the HPs of A. alternata. While analyzing the proteome data, 29 potential allergens were predicted by AlgPred and further screening in SDAP confirmed the allergic response of 10 proteins. Extensive bioinformatics tools including protein family classification, sequence-function relationship, protein motif discovery, pathway interactions, and intrinsic features from the amino acid sequence were used to successfully predict the probable functions of the 10 HPs. The functions of the HPs are characterized as chitin-binding, ribosomal protein P1, thaumatin, glycosyl hydrolase, and NOB1 proteins. The subcellular localization and signal peptide prediction of these 10 proteins has further provided additional information on localization and function. The allergens prediction and functional annotation of the 10 proteins may facilitate a better understanding of the allergenic mechanism of A. alternata in asthma and other diseases. The functional domain level insights and predicted structural features of the allergenic proteins help to understand the pathogenesis and host immune tolerance. The outcomes of the study would aid in the development of specific drugs to combat A. alternata infections.

Inhibitory effect of benzocaine from Schisandra chinensis on Alternaria alternata.

The clinical effects of Schisandra chinensis against human disease are well-documented; however, studies on its application in controlling plant pathogens are limited. Here, we investigated its inhibitory effect on the growth of Alternaria alternata, a fungus which causes significant post-harvest losses on apples, known as black spot disease. S. chinensis fruit extract exhibited strong inhibitory effects on the growth of A. alternata with an EC50 of 1882.00 mg/L. There were 157 compounds identified in the extract by high performance liquid chromatography-mass spectrometry, where benzocaine constituted 14.19% of the extract. Antifungal experiments showed that the inhibitory activity of benzocaine on A. alternata was 43.77-fold higher than the crude extract. The application of benzocaine before and after A. alternata inoculation on apples prevented the pathogen infection and led to mycelial distortion according to scanning electron microscopy. Transcriptome analysis revealed that there were 4226 genes differentially expressed between treated and untreated A. alternata-infected apples with benzocaine. Metabolomics analysis led to the identification of 155 metabolites. Correlation analysis between the transcriptome and metabolome revealed that benzocaine may inhibit A. alternata growth via the beta-alanine metabolic pathway. Overall, S. chinensis extract and benzocaine are environmentally friendly plant-based fungicides with potential to control A. alternata.

Alternaria diseases on potato and tomato.

Alternaria spp. cause different diseases in potato and tomato crops. Early blight caused by Alternaria solani and brown spot caused by Alternaria alternata are most common, but the disease complex is far more diverse. We first provide an overview of the Alternaria species infecting the two host plants to alleviate some of the confusion that arises from the taxonomic rearrangements in this fungal genus. Highlighting the diversity of Alternaria fungi on both solanaceous hosts, we review studies investigating the genetic diversity and genomes, before we present recent advances from studies elucidating host-pathogen interactions and fungicide resistances. TAXONOMY: Kingdom Fungi, Phylum Ascomycota, Class Dothideomycetes, Order Pleosporales, Family Pleosporaceae, Genus Alternaria. BIOLOGY AND HOST RANGE: Alternaria spp. adopt diverse lifestyles. We specifically review Alternaria spp. that cause disease in the two solanaceous crops potato (Solanum tuberosum) and tomato (Solanum lycopersicum). They are necrotrophic pathogens with no known sexual stage, despite some signatures of recombination. DISEASE SYMPTOMS: Symptoms of the early blight/brown spot disease complex include foliar lesions that first present as brown spots, depending on the species with characteristic concentric rings, which eventually lead to severe defoliation and considerable yield loss. CONTROL: Good field hygiene can keep the disease pressure low. Some potato and tomato cultivars show differences in susceptibility, but there are no fully resistant varieties known. Therefore, the main control mechanism is treatment with fungicides.

The HOG-pathway related AaOS1 leads to dicarboximide-resistance in field strains of Alternaria alternata and contributes, together with the Aafhk1, to mycotoxin production and virulence.

BACKGROUND: Garlic leaf spot (GLS) caused by Alternaria alternata is one of the main diseases in the garlic production areas, and its management heavily relies on dicarboximide fungicides. However, the efficacy of dicarboximides against the GLS disease has decreased year on year. RESULTS: In the present study, 10 of 148 A. alternata strains separated from Jiangsu Province were moderately resistant (MR) to a dicarboximide fungicide procymidone (ProMR). Positive cross-resistance was observed between Pro and iprodione (Ipro) or fludioxonil (Fld), but not between Pro and fluazinam or azoxystrobin. Mutations at AaOS1, but not Aafhk1, were confirmed to confer the Pro resistance by constructing replacement mutants, whereas mutations at both AaOS1 and Aafhk1 decreased the gene expression level of AapksI, as well as the ability to produce mycotoxin AOH (polyketide-derived alternariol) and virulence. Additionally, more genes (AaOS1 and Aafhk1) harboring the mutations experienced a larger biological fitness penalty. CONCLUSION: To our knowledge, this is the first report on Pro resistance selected in garlic fields, and mutations at AaOS1 of A. alternata causing a decreased ability to produce the mycotoxin AOH. © 2024 Society of Chemical Industry.

Integrating CRISPR-Cas12a and rolling circle-amplified G-quadruplex for naked-eye fluorescent "off-on" detection of citrus Alternaria.

Alternaria is a plant pathogen that spreads globally and is prone to causing citrus brown spot disease and metabolizing mycotoxins, thus seriously hindering the development of this economic crop industry. Herein, a "label-free" and "turn on" visual fluorescent assay for citrus Alternaria based on CRISPR-Cas12a and rolling circle amplification (RCA) was described. Using ssDNA complementary to RCA primer as a trans-cleavage substrate for CRISPR-Cas12a, the two systems of CRISPR-Cas12a and RCA-amplified G-quadruplex were skillfully integrated. By using a portable light source for excitation, the positive sample produced obvious red fluorescence, while the negative sample remained almost colorless, making them easy to differentiate with the naked eye. In addition, the specificity was demonstrated by distinguishing Alternaria from other citrus disease related pathogens. Moreover, the practicality was verified by analyzing cultured Alternaria and Alternaria in actual citrus leaf and fruit samples. Therefore, this method may contribute to the on-site diagnosis of Alternaria.

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.

Identification and distribution of a fungal endosymbiotic Alternaria species (Alternaria section Undifilum sp.) in Astragalus garbancillo tissues.

Plants belonging to the genera Astragalus, Oxytropis, Ipomoea, Sida, and Swainsona often contain the toxin swainsonine (SW) produced by an associated fungal symbiont. Consumption of SW-containing plants causes a serious neurological disorder in livestock, which can be fatal. In this study, a fungal endophyte, Alternaria section Undifilum, was identified in Astragalus garbancillo seeds, using polymerase chain reaction (PCR) followed by direct sequencing. In seeds, the SW concentrations were about 4 times higher than in other parts of the plant. Furthermore, microscopic examination demonstrated that the fungus mycelium grows inside the petioles and stems, on the outer surface and inside the mesocarp of the fruit, in the mesotesta and endotesta layers of the seed coat, and inside the endosperm of the seeds. Our results support the notion that the SW-producing fungus is vertically transmitted in the host plant A. garbancillo.

Genotyping-by-Sequencing Reveals Population Differentiation and Linkage Disequilibrium in Alternaria linariae from Tomato.

Alternaria linariae is an economically important foliar pathogen that causes early blight disease in tomatoes. Understanding genetic diversity, population genetic structure, and evolutionary potential is crucial to contemplating effective disease management strategies. We leveraged genotyping-by-sequencing (GBS) technology to compare genome-wide variation in 124 isolates of Alternaria spp. (A. alternata, A. linariae, and A. solani) for comparative genome analysis and to test the hypotheses of genetic differentiation and linkage disequilibrium (LD) in A. linariae collected from tomatoes in western North Carolina. We performed a pangenome-aware variant calling and filtering with GBSapp and identified 53,238 variants conserved across the reference genomes of three Alternaria spp. The highest marker density was observed on chromosome 1 (7 Mb). Both discriminant analysis of principal components and Bayesian model-based STRUCTURE analysis of A. linariae isolates revealed three subpopulations with minimal admixture. The genetic differentiation coefficients (FST) within A. linariae subpopulations were similar and high (0.86), indicating that alleles in the subpopulations are fixed and the genetic structure is likely due to restricted recombination. Analysis of molecular variance indicated higher variation among populations (89%) than within the population (11%). We found long-range LD between pairs of loci in A. linariae, supporting the hypothesis of low recombination expected for a fungal pathogen with limited sexual reproduction. Our findings provide evidence of a high level of population genetic differentiation in A. linariae, which reinforces the importance of developing tomato varieties with broad-spectrum resistance to various isolates of A. linariae.

AaLaeA targets AaFla1 to mediate the production of antitumor compound in Alternaria alstroemeria.

Endophytic fungi are an important source of novel antitumor substances. Previously, we isolated an endophytic fungus, Alternaria alstroemeria, from the medicinal plant Artemisia artemisia, whose crude extracts strongly inhibited A549 tumor cells. We obtained a transformant, namely AaLaeAOE26 , which completely loses its antitumor activity due to overexpression of the global regulator AaLaeA. Re-sequencing analysis of the genome revealed that the insertion site was in the noncoding region and did not destroy any other genes. Metabolomics analysis revealed that the level of secondary antitumor metabolic substances was significantly lower in AaLaeAOE26 compared with the wild strain, in particular flavonoids were more downregulated according to the metabolomics analysis. A further comparative transcriptome analysis revealed that a gene encoding FAD-binding domain protein (Fla1) was significantly downregulated. On the other hand, overexpression of AaFla1 led to significant enhancement of antitumor activity against A549 with a sevenfold higher inhibition ratio than the wild strain. At the same time, we also found a significant increase in the accumulation of antitumor metabolites including quercetin, gitogenin, rhodioloside, liensinine, ginsenoside Rg2 and cinobufagin. Our data suggest that the global regulator AaLaeA negatively affects the production of antitumor compounds via controlling the transcription of AaFla1 in endophytic A. alstroemeria.

First Report of Alternaria alternata Causing Decay in Exported Sweet Basil During Freight from Israel to Europe.

Sweet basil (Ocimum basilicum) is an important spice herb grown in Israel for local markets and export. The crop is used as a fresh culinary herb or spice, and the essential oils are used in cosmetics and food flavorings. Due to increased demand, the production area of basil has increased in Israel. Postharvest losses due to fungal disease are a major economic concern for growers. In the summer of 2019, a leaf spot was observed in postharvest shipments of sweet basil destined for Europe; in late winter of 2022, leaf spots were observed on greenhouse-grown sweet basil. Fungal isolates from infected leaves were characterized by morphology in culture as Alternaria spp. PCR amplification of the Alternaria major allergen Alt a1, ITS, and gdp gene regions of the recovered isolates confirmed the presence of A. alternata, a common pathogen of numerous herbs and spice plants. In vitro growth tests demonstrated that 25°C was the optimum temperature for growth of the isolates. The isolates were tested for pathogenicity and found to infect a commonly grown cultivar of basil, cultivar Eli (previously cultivar Perrie). Foliar symptoms in pathogenicity tests were identical to those observed in commercial shipments and in the field, which completed Koch's postulates. Control of the nascent disease by applying fungicides to the plants may be necessary to reduce postharvest losses.

Three point mutations in AaCYP51 combined with induced overexpression of AaCYP51 conferred low-level resistance to mefentrifluconazole in Alternaria alternata.

Tomato early blight is a significant disease that causes substantial losses to tomato yield and quality. Mefentrifluconazole, an isopropanol-azole subgroup of triazole fungicides, has been registered in China for controlling various plant diseases, including tomato early blight, grape anthracnose, and apple brown spot. However, limited information is available on the mefentrifluconazole resistance risk and mechanism in plant pathogens. The sensitivity to mefentrifluconazole of 122 isolates of Alternaria alternata, one of the causal agents of tomato early blight, collected from different provinces in China, was evaluated. The results showed a unimodal curve for the sensitivity frequency, with an average EC50 of 0.306 µg/mL. Through fungicide adaption, six resistant mutants (N4, N5, T4, T5, NG1, and NG10) were obtained from three parental isolates, with a mutation frequency of 3.28 × 10-4 and resistance factors ranging between 19 and 147. The survival fitness of the resistant mutants, except for NG1, was significantly lower than that of their parental isolates. Positive cross-resistance was observed between mefentrifluconazole and difenoconazole or fenbuconazole, whereas no cross-resistance was found with three non-DMI fungicides. Furthermore, three distinct point mutations were detected in the AaCYP51 protein of the resistant mutants: I300S in T4 and T5; A303T in N4, NG1, and NG10; and A303V in N5. Compared to the parental isolates, the AaCYP51 gene was overexpressed in all six resistant mutants when treated with mefentrifluconazole. In summary, the resistance risk of A. alternata to mefentrifluconazole was low, and point mutations and overexpression of the AaCYP51 gene were identified as contributing factors to mefentrifluconazole resistance in A. alternata.

Complete genome sequence of the carrot black rot pathogen Alternaria radicina isolate CBR2.

Black rot, caused by Alternaria radicina, seriously endangers carrots throughout the growing season, affecting both leaves and fleshy roots. In this study, we sequenced and assembled the genome of the A. radicina isolate CBR2. The genome was 34.6 Mb in size and consisted of 6 scaffolds. The sequence information provided in this genome will be used as a reference for further comparative genomics analysis of Alternaria species and will contribute to disease control in carrot production.

Conserved copper regulation of the antimicrobial isocyanide brassicicolin A in Alternaria brassicicola.

Phytopathogenic Alternaria species are renown for production of toxins that contribute to virulence on host plants. Typically, these toxins belong to well-known secondary metabolite chemical classes including polyketides, non-ribosomal peptides and terpenes. However, the purported host toxin brassicicolin A produced by A. brassicicola is an isocyanide, a chemical class whose genetics and encoding gene structure is largely unknown. The chemical structure of brassicicolin A shows it to have similarity to the recently characterized fumicicolins derived from the Aspergillus fumigatus isocyanide synthase CrmA. Examination of the A. brassicicola genome identified AbcrmA, a putative homolog with 64% identity to A. fumigatus CrmA. Deletion of AbcrmA resulted in loss of production of brassicicolin A. Contrary to reports that brassicicolin A is a host-specific toxin, the ΔAbcrmA mutants were equally virulent as the wildtype on Brassica hosts. However, in line with results of A. fumigatus CrmA generated metabolites, we find that brassicicolin A increased 360-fold under copper limited conditions. Also, like A. fumigatus CrmA derived metabolites, we find brassicicolin A to be a broad-spectrum antimicrobial. We speculate that CrmA-like isocyanide synthase products provide the producing fungi a fitness advantage in copper depleted environments.

Molecular characterization and antifungal activity of lipopeptides produced from Bacillus subtilis against plant fungal pathogen Alternaria alternata.

Over 380 host plant species have been known to develop leaf spots as a result of the fungus Alternaria alternata. It is an aspiring pathogen that affects a variety of hosts and causes rots, blights, and leaf spots on different plant sections. In this investigation, the lipopeptides from the B. subtilis strains T3, T4, T5, and T6 were evaluated for their antifungal activities. In the genomic DNA, iturin, surfactin, and fengycin genes were found recovered from B. subtilis bacterium by PCR amplification. From different B. subtilis strains, antifungal Lipopeptides were extracted, identified by HPLC, and quantified with values for T3 (24 g/ml), T4 (32 g/ml), T5 (28 g/ml), and T6 (18 g/ml). To test the antifungal activity, the isolated lipopeptides from the B. subtilis T3, T4, T5, and T6 strains were applied to Alternaria alternata at a concentration of 10 g/ml. Lipopeptides were found to suppress Alternaria alternata at rates of T3 (75.14%), T4 (75.93%), T5 (80.40%), and T6 (85.88%). The T6 strain outperformed the other three by having the highest antifungal activity against Alternaria alternata (85.88%).

[Identification and biological characterization of pathogen causing black spot of Pseudostellaria heterophylla in Fujian province].

In Zherong county, Fujian province, the black spot of Pseudostellaria heterophylla often breaks out in the rainy season from April to June every year. As one of the main leaf diseases of P. heterophylla, black spot seriously affects the yield and quality of the medicinal material. To identify and characterize the pathogens causing black spot, we isolated the pathogens, identified them as a species of Alternaria according to Koch's postulates, and then tested their pathogenicity and biological characteristics. The results showed that the pathogens causing P. heterophylla black spot were A. gaisen, as evidenced by the similar colony morphology, spore characteristics, sporulation phenotype, and the same clade with A. gaisen on the phylogenetic tree(the maximum likelihood support rate of 100% and the Bayesian posterior probability of 1.00) built based on the tandem sequences of ITS, tef1, gapdh, endoPG, Alta1, OPA10-2, and KOG1077. The optimum conditions for mycelial growth of the pathogen were 25 ℃, pH 5-8, and 24 h dark culture. The lethal conditions for mycelia and spores were both treatment at 50 ℃ for 10 min. We reported for the first time the A. gaisen-caused black spot of P. heterophylla. The results could provide a theoretical basis for the diagnosis and control of P. heterophylla leaf spot diseases.

Alternaria gansuense, a Plant Systematic Fungal Pathogen Producing Swainsonine in Vivo and in Vitro.

Astragalus adsurgens (A. adsurgens), which is considered a forage in China, grows widely in Eurasia and North America. However, Alternaria gansuense (A. gansuense) (synonym: Embellisia astragali) systematically infects A. adsurgens, producing swainsonine (SW), which poisons domesticated animals. In this study, we hypothesized that the A. gansuense SW-producing fungus is morphologically and molecularly related to the locoweed endophyte, Alternaria oxytropis (A. oxytropis), which systematically grows in host plants. Therefore, pure cultures of the fungi from diseased plants or endophytic interactions were collected from fields and assayed for SW via high-performance liquid chromatography linked to mass spectroscopy (HPLC-MS). The production of SW was also detected in A. adsurgens, A. oxytropis and diseased plants by assaying for the presence of the ß-ketoacyl synthase (KS) gene, which is required for SW synthesis. Diseased A. adsurgens and pure cultures of A. gansuense have SW and the healthy-looking A. adsurgens plants also contained SW, probably because they were infected with A. gansuense. Therefore, A. adsurgens-infected A. gansuense are not safe for livestock consumption.

Using qPCR and microscopy to assess the impact of harvesting and weather conditions on the relationship between Alternaria alternata and Alternaria spp. spores in rural and urban atmospheres.

Alternaria is a plant pathogen and human allergen. Alternaria alternata is one of the most abundant fungal spores in the air. The purpose of this study was to examine whether Alternaria spp. spore concentrations can be used to predict the abundance and spatio-temporal pattern of A. alternata spores in the air. This was investigated by testing the hypothesis that A. alternata dominates airborne Alternaria spp. spores and varies spatio-temporally. Secondarily, we aimed at investigating the relationship between airborne Alternaria spp. spores and the DNA profile of A. alternata spores between two proximate (~ 7 km apart) sites. These were examined by sampling Alternaria spp. spores using Burkard 7-day and cyclone samplers for the period 2016-2018 at Worcester and Lakeside campuses of the University of Worcester, UK. Daily Alternaria spp. spores from the Burkard traps were identified using optical microscopy whilst A. alternata from the cyclone samples was detected and quantified using quantitative polymerase chain reaction (qPCR). The results showed that either A. alternata or other Alternaria species spores dominate the airborne Alternaria spore concentrations, generally depending on weather conditions. Furthermore, although Alternaria spp. spore concentrations were similar for the two proximate sites, A. alternata spore concentrations significantly varied for those sites and it is highly likely that the airborne samples contained large amounts of small fragments of A. alternata. Overall, the study shows that there is a higher abundance of airborne Alternaria allergen than reported by aerobiological networks and the majority is likely to be from spore and hyphal fragments.

Small-spored Alternaria spp. (section Alternaria) are common pathogens on wild tomato species.

The wild relatives of modern tomato crops are native to South America. These plants occur in habitats as different as the Andes and the Atacama Desert and are, to some degree, all susceptible to fungal pathogens of the genus Alternaria. Alternaria is a large genus. On tomatoes, several species cause early blight, leaf spots and other diseases. We collected Alternaria-like infection lesions from the leaves of eight wild tomato species from Chile and Peru. Using molecular barcoding markers, we characterized the pathogens. The infection lesions were caused predominantly by small-spored species of Alternaria of the section Alternaria, like A. alternata, but also by Stemphylium spp., Alternaria spp. from the section Ulocladioides and other related species. Morphological observations and an infection assay confirmed this. Comparative genetic diversity analyses show a larger diversity in this wild system than in studies of cultivated Solanum species. As A. alternata has been reported to be an increasing problem in cultivated tomatoes, investigating the evolutionary potential of this pathogen is not only interesting to scientists studying wild plant pathosystems. It could also inform crop protection and breeding programs to be aware of potential epidemics caused by species still confined to South America.