Interacting Abiotic Factors Affect Growth and Mycotoxin Production Profiles of Alternaria Section Alternaria Strains on Chickpea-Based Media

Chickpea is susceptible to fungal infection and mycotoxin contamination. Argentina exports most of its chickpea production; thus, its quality is of concern. The Alternaria fungal genus was found to be prevalent in chickpea samples from Argentina. The species within this genus are able to produce mycotoxins, such as alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TA). In this context, we evaluated the effect of water activity (0.99, 0.98, 0.96, 0.95, 0.94, 0.92, and 0.90 a_W), temperature (4, 15, 25, and 30 °C), incubation time (7, 14, 21, and 28 days), and their interactions on mycelial growth and AOH, AME, and TA production on chickpea-based medium by two A. alternata strains and one A. arborescens strain isolated from chickpea in Argentina. Maximum growth rates were obtained at the highest a_W (0.99) and 25 °C, with growth decreasing as the a_W of the medium and the temperature were reduced. A. arborescens grew significantly faster than A. alternata. Mycotoxin production was affected by both variables (a_W and temperature), and the pattern obtained was dependent on the strains/species evaluated. In general, both A. alternata strains produced maximum amounts of AOH and AME at 30 °C and 0.99-0.98 a_W, while for TA production, both strains behaved completely differently (maximum levels at 25 °C and 0.96 a_W for one strain and 30 °C and 0.98 a_W for the other). A. arborescens produced maximum amounts of the three toxins at 25 °C and 0.98 a_W. Temperature and a_W conditions for mycotoxin production were slightly narrower than those for growth. Temperature and a_W conditions assayed are those found during chickpea grain development in the field, and also could be present during storage. This study provides useful data on the conditions representing a risk for contamination of chickpea by Alternaria toxins.

Exploration of lung mycobiome in the patients with non-small-cell lung cancer

As the Human Microbiome Project (HMP) progresses, the relationship between microbes and human health has been receiving increasing attention. A growing number of reports support the correlation between cancer and microbes. However, most studies have focused on bacteria, rather than fungal communities. In this study, we studied the alteration in lung mycobiome in patients with non-small-cell lung cancer (NSCLC) using metagenomic sequencing and qPCR. The higher fungal diversity and more complex network were observed in the patients with NSCLC. In addition, Alternaria arborescens was found as the most relevant fungus to NSCLC, and the enrichment of it in cancerous tissue was also detected. This study proposes that the changes in fungal communities may be closely related to lung cancer, and provides insights into further exploration the relationship between lung cancer and fungi.

Aggressiveness of Small-Spored Alternaria spp. and Their Sensitivity to Succinate Dehydrogenase Inhibitor Fungicides

Brown leaf spot of potato is caused by a number of small-spored Alternaria spp. Alternaria alternata sensu stricto, A. arborescens, and A. tenuissima have been reported with increasing frequency in commercial potato fields. Potato cultivars with resistance to small-spored Alternaria spp. have yet to be developed; therefore, the application of foliar fungicides is a primary management strategy. Greenhouse inoculation assays demonstrated that isolates of these three small-spored Alternaria spp. were pathogenic. Significant differences in aggressiveness were observed across isolates; however, there was no trend in aggressiveness based on species. Significant fungicide by isolate interactions in in vitro fungicide sensitivity and significant differences between baseline and nonbaseline isolates were observed in all three small-spored Alternaria spp. The ranges of in vitro sensitivity of A. alternata baseline isolates to boscalid (EC₅₀ <0.010 to 0.89 µg/ml), fluopyram (<0.010 to 1.14 µg/ml) and solatenol (<0.010 to 1.14 µg/ml) were relatively wide when compared with adepidyn (<0.010 to 0.023 µg/ml). The baseline sensitivities of A. arborescens and A. tenuissima isolates to all four fungicides were <0.065 µg/ml. Between 10 and 21% of nonbaseline A. alternata isolates fell outside the baseline range established for the four succinate dehydrogenase inhibitor (SDHI) fungicides evaluated. In A. arborescens, 10 to 80% of nonbaseline isolates had higher sensitivities than the baseline. A. tenuissima isolates fell outside the baseline for boscalid (55%), fluopyram (14%), and solatenol (14%), but none fell outside the baseline range for adepidyn. Evaluations of in vivo fungicide efficacy demonstrated that most isolates were equally controlled by the four SDHI fungicides. However, reduced boscalid efficacy was observed for four isolates (two each of A. arborescens and A. tenuissima) and reduced fluopyram control was observed in one A. alternata isolate. Results of these studies demonstrate that isolates of all three species could be contributing to the brown leaf spot pathogen complex and that monitoring both species diversity and fungicide sensitivity could be advantageous for the management of brown leaf spot in potatoes with SDHI fungicides.

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.

First Report of Moldy Core of Sweet Tango Apples from New Zealand Caused by Alternaria arborescens

Moldy core is a fungal disease of apple fruits that is characterized by mycelial growth in the seed locules and is sometimes accompanied by penetration of the immediate surrounding flesh. The disease can go undetected until the fruit is cut open, as no external symptoms appear on the fruit. Alternaria, Aspergillus, Cladosporium, Coniothyrium, Epicoccum, Phoma and Stemphylium are some of the common pathogens associated with moldy core (Serdani et al. 2002; Gao et al. 2013; McLeod 2014). The disease is more common in apple cultivars with an open calyx, where spores may initiate infections during the growing season or at the post-harvest storage stage (Spotts et al. 1988). In 2018, a shipment of 'Sweet Tango' apples from New Zealand to Scotian Gold Co-operative Ltd., Nova Scotia, Canada, was found to be affected by moldy core. Moderate to severe moldy core symptoms were observed when 10 apples were cut open (Figure S1). In comparison, 'Sweet Tango' apples grown in Nova Scotia showed no moldy core symptoms when 10 random fruits were cut open. Small pieces of the diseased fruit tissue from the core region were surface-disinfected for 1 min in 1% NaOCl, rinsed three times with sterilized water and placed onto potato dextrose agar (PDA) dishes. The PDA dishes were incubated in dark at 22 oC and single spore isolation was carried out to fresh PDA dishes. These isolate produced colonies of regular shape, tan black with prominent white gray margin and gray colour conidia (Figure S2 AB). The colonies turn dark black after 3 weeks of growth on PDA. Mycelia were septate and conidia were oval or obclavate or club-shaped with a tapering end with 4-6 longitudinal and transverse septa (Figure S2 C-D). The size of conidia ranges from 12.5-20 x 8.7-12.5 µM on 20 days old PDA dishes. Based on the size and shape of conidia and other morphological characteristics the isolated fungi were identical to Alternaria spp. (Simmons 2007). To assess the identity of the isolated pathogen species by multi-locus sequence analysis, genomic DNA was extracted from the pure cultures of two isolates (5.8 and 8) using the E.Z.N.A. SP Fungal DNA Kit (Omega Bio-Tek). The glyceraldehyde-3-phosphate dehydrogenase (GAPDH), major allergen (Alt a 1), OPA10-2, the internal transcribed spacer (ITS) region of ribosomal DNA and the translation elongation factor 1-α (TEF1-α) region from two Alternaria spp. isolates (5.8 and 8) were amplified and sequenced using primers gpd1/2 (Berbee et al. 1999), A21F/A21R (Gabriel 2015), OPA10-2/ OPA10-2L (Andrew et al. 2009), ITS1/ITS4 (White et al. 1990) and EF1-up /EF1-low (O'Donnell et al. 1998) respectively. The resulting sequences of both isolates were deposited in the NCBI GenBank (GAPDH; MW411052, MW411053, Alt a 1; MW411050, MW411051, OPA10-2; MW415762, MW415763, ITS; MK140445, MT225559, TEF1-α; MT305773 and MT305774 ). Sequences of GAPDH, Alt a 1, OPA-10-2, ITS and TEF1-α genes of both isolates were identical to each other and showed 100 %, 100 %, 99.21 %, 100% and 100% identity to A. arborescens S. (AY278810.1, AY563303.1, KP124712.1, KY965831.1, KY965831.1) respectively. Identity with reference strain CBS 102605 confirms that both of the isolated strains 5.8 and 8 are A. arborescens. The pathogenicity of the two A. arborescens isolates were confirmed by artificially inoculating healthy 'Sweet Tango' fruit by dispensing the conidial suspension directly on the seed locule. Briefly, surface-disinfected fruits were air-dried for 5 min and then peeled using a sterilized knife and cut transversally. Each half of the fruit was inoculated with 100 µl of conidial suspensions (∼1 × 104 conidia/ml) in potato dextrose broth (PDB) and incubated at 22 °C in a humid chamber for 7-10 days, or until symptoms with visible mycelial growth were observed. The control fruits were treated with 100 µl of sterilized PDB. Both A. arborescens isolates produced visible moldy core symptoms on the inoculated 'Sweet Tango' fruits, whereas no symptoms were observed on the control fruits (Figure S1). The experiment was repeated three times with at least three replicates with similar results. A. arborescens was successfully re-isolated from the artificially-inoculated fruits to complete Koch's postulates. To our knowledge, this is the first report of Alternaria arborescens causing moldy core disease in 'Sweet Tango' apples from New Zealand. Acknowledgments We thank Eric Bevis for his help in sample preparation for DNA sequencing, Willy Renderos for pathogenicity assay. We also thank Joan Hebb (Scotian Gold Cooperative Ltd.,) for providing the apple sample for this study. This research was made possible through financial support from Agriculture and Agri-Food Canada. The authors(s) declare no conflict of interest. Literature Cited Andrew M., Peever T.L., Pryor B.M. An expanded multilocus phylogeny does not resolve species among the small-spored Alternaria species complex. 2009. Mycologia. 101:95-109. Berbee, M. L. et al. 1999. Cochliobolus phylogenetics and the origin of known, highly virulent pathogens, inferred from ITS and glyceraldehyde-3-phosphate dehydrogenase gene sequences Mycologia. 91:964. Gabriel, M.F. I. Postigo, A. Gutiérrez-Rodríguez, E. Suñén, C.T. Tomaz, J. Martínez 2015. Development of a PCR-based tool for detecting immunologically relevant Alt a 1 and Alt a 1 homologue coding sequences. Medical Mycology. 53 (6):636-642. Gao, L. L., Zhang, Q., Sun, X. Y., Jiang, L., Zhang, R., Sun, G. Y., Zha, Y. L., and Biggs, A. R. 2013. Etiology of moldy core, core browning, and core rot of Fuji apple in China. Plant Dis. 97:510-516. Kerry, O'Donnell, H.C. Kistler, E. Cigelnik, R.C. Ploetz. 1998. Multiple evolutionary origins of the fungus causing Panama disease of banana: concordant evidence from nuclear and mitochondrial gene genealogies. PNAS. 95: 2044-2049. McLeod, A. 2014. Moldy core and core rots. Pages 40-41 in: Compendium of Apple and Pear Diseases and Pests, 2nd ed. T. B. Sutton, H. S. Aldwinckle, A. M. Agnello, and J. F. Walgenbach, eds. American Phytopathological Society, St Paul, MN. Serdani, M., Kang, J. C., Peever, T. L., Andersen, B., and Crous, P. W. 2002. Characterization of Alternaria species groups associated with core rot of apples in South Africa. Mycol. Res. 106:561-569. Simmons, E. G. 2007. Alternaria: an identification manual. CBS Biodiversity Series. 6:780 pp. Spotts, R. A., Holmes, R. J., and Washington, W. S. 1988. Factors affecting wet core rot of apples. Australas. Plant Pathol. 17:53-57. White, T. J., Bruns, T., Lee, S., and Taylor, J. 1990. Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics. Pages 315-322 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis, D. H. Gelfand, J. J. Sninsky, and T. J. White, eds. San Diego, CA: Academic Press. Woudenberg, J. H. C., et al. 2015. Alternaria section Alternaria: Species, formae speciales or pathotypes. Stud. Mycol. 82:1-21.

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.

Computational identification and antifungal bioassay reveals phytosterols as potential inhibitor of Alternaria arborescens

Alternaria arborescens is a major pathogen for crops like tomato, tangerine and so on and its control is mostly dependent on the application of chemical agents. Plants as the sources of natural products are very attractive option for developing eco-friendly and natural antifungal agents. In this study, we modeled three-dimensional structure of chorismate synthase (CS) enzyme from A. arborescens. Docking studies of phytosterols, namely, γ-sitosterol and β-sitosterol, with CS showed them to be potential inhibitor of CS. To explore the stability and conformational flexibility of all the AaCS complex systems, molecular dynamics simulations were performed. None of the putative inhibitors as well as β- and γ-sitosterol showed interaction with the FMNH₂ binding pocket of the tomato CS (major host of A. arborescens) indicating their suitability as antifungal compounds inhibiting the shikimate pathway without causing any harm to the host. An in vivo antifungal bioassay showed a significant reduction in fungal growth in the presence of β-sitosterol (500 ppm) which resulted in ∼23% and ∼17% reduction in fungal fresh and dry weight, respectively, at 8 days after inoculation. This study provides experimental evidence establishing natural sterols like β-sitosterol can be useful in curbing A. arborescens damage in an eco-friendly manner.Communicated by Ramaswamy H. Sarma.

Genome-Wide Analysis of Microsatellites in Alternaria arborescens and Elucidation of the Function of Polyketide Synthase (PksJ)

Microsatellites or simple sequence repeats (SSRs) have been the most widely applied class of molecular markers used in genetic studies, having applications in genetic conservation, population studies, as well as diagnostics of fungi. Mining and analysis of SSRs of the whole genome sequence have been carried out in this study for the fungus Alternaria arborescens causing early blight of tomato and well known for producing mycotoxins like alternariol (AOH), alternariol monomethyl ether (AME), etc. A total of 4097 microsatellites were identified in A. Arborescens genome. Contig 1 was identified as the most SSR-rich region which was further analyzed to correlate the presence of SSRs with different biological processes. A total of 246 putative genes were predicted in this study and KEGG pathway analysis of 155 predicted genes indicated that SSRs can be linked with important metabolic pathways, molecular functioning, signal transduction, and cellular processes. The prediction of fungal mycotoxin inducer gene Polyketide synthase (PksJ) linked with SSR in this study may be a potential candidate participating in oncogenic signal transduction in human. Our study is the first report of PksJ gene in A. arborescens, a precursor of AOH and AME.