Ascomycete Fungi (Alternaria spp.) Characterization as Major Feed Grains Pathogens

Published: September 15, 2021

By: Nikola Puvaca 1, Vojislava Bursic 2, Gorica Vukovic 3, Dragana Budakov 2, Aleksandra Petrovic 2, Jordan Merkuri 4, Giuseppina Avantaggiato 5 and Magdalena Cara 4.

Summary

Author details:

1 Department of Engineering Management in Biotechnology, Faculty of Economics and Engineering Management in Novi Sad, University Business Academy in Novi Sad, Cvećarska 2, 21000 Novi Sad, Serbia; 2 Faculty of Agriculture, University of Novi Sad, Trg Dositeja Obradovića 8, 21000 Novi Sad, Serbia; 3 Institute of Public Health of Belgrade, Bulevar despota Stefana 54a, 11000 Belgrade, Serbia; 4 Faculty of Agriculture and Environment, Agricultural University of Tirana, Kodor Kamez, 1000 Tirana, Albania 5 Institute of Sciences of Food Production (ISPA), National Research Council (CNR), Via Amendola, 70126 Bari, Italy.

The emergence of new infectious plant diseases is driven by anthropogenic and environmental change, including trade, land use, and climate changes. The movement of infected plant material through trade in plant products, germplasm, grafts, and live plants has been recognized as the most significant contributing factor to the emergence of new plant diseases. Alternaria spp. are ubiquitous fungi. They are present in the human and animals' environment, being commonly found in environmental dust samples and air conditioning systems, while spore traps often show evidence of Alternaria dispersal. Alternaria spp. have even been shown to be associated with insects, having been isolated from the backs of cockroaches. Little work has been performed to investigate the saprotrophic lifestyle of Alternaria spp., which probably accounts for the majority of Alternaria species in nature. Alternaria spp. can persist on low nutrient media, suggesting that they can complete their lifecycle in poor nutrient environments. This review aims to present the lifestyle of ascomycete fungi such as Alternaria spp. and show their characterization as major feed grains pathogens in agricultural feed production.

Keywords: mycotoxins; wheat; Alternaria; fungi; feed; toxins.

1. Introduction

The appearance of new transmittable plant diseases is determined by anthropogenic and conservational change, including changes in trade, land use, and climate [1–4]. The growth of infected plant material through trade in plant products, germplasm, grafts, and live plants has been recognised as the greatest contributing factor to the emergence of new plant diseases [5–7]. A pathogen may be introduced without disease emergence initially until a second factor, such as the introduction of disease vectors, more appropriate hosts, or changes in the environment, leads to an increase in disease incidence, geographic range, or severity [8]. Fungi are responsible for many introduced plant diseases, with more fungal infections introduced to Europe and Africa over the 20th Century than bacteria and viruses combined [9]. Understanding the evolutionary history, evolutionary potential, and pathogenicity of fungal diseases will help manage and identify emerging pathogens [10].

Alternaria spp. are ubiquitous fungi [11]. They are present in the human and animals' environment, being commonly found in environmental dust samples and air conditioning systems, while spore traps often show evidence of Alternaria dispersal [12]. Alternaria spp. have even been shown to be associated with insects, having been isolated from the backs of cockroaches [13]. Little work has been performed to investigate the saprotrophic lifestyle of Alternaria spp., which probably accounts for the majority of Alternaria species in nature. Alternaria spp. can persist on low nutrient media, suggesting that they can complete their lifecycle in poor nutrient environments [14]. Alternaria is best known for its role as plant pathogens. The USDA Fungal Host Index contains over 4,000 plant-host associations in this genus, ranking it 10th in the total number of host associations of nearly 2000 fungal genera. The Alternaria alternata species group alone is recorded as causing disease on over 100 host plants. This includes economically essential crops including cereals, ornamentals, vegetables, and fruits, with losses incurred through direct crop damage, postharvest spoilage, or through contamination with mycotoxins [15].

Alternaria infections usually occur on the leaves and stems of the host plant [16]. Leaf spots are recognized by black necrotic lesions surrounded by chlorotic halos. Leaf necrosis may lead to reduced marketability for leafy crops such as Brassica. It may also result in the host abscising leaves, reducing photosynthetic potential and crop yields indirectly, as is the case in apple and pear [17]. Alternaria spp. also causes fruit spot. They are leading to reduced crop marketability, a significant problem in citrus fruits. Alternaria spp. also incurs economic losses postharvest [18,19]. In Red Delicious varieties of apple in South Africa, annual losses of 6-8% have been attributed to Alternaria dry core rot. Such postharvest diseases are often not thought to be attributed to a single Alternaria sp. but may be caused by a range of species. Infections of wheat grains by Alternaria spp. occur in the field and in storage, where low temperatures favor them. This reflects the saprotrophic/opportunistic necrotrophic lifestyle common through Alternaria species [20].

Postharvest spoilage may not just be a result of visual blemishes or reduced palatability but may also be caused by mycotoxin contamination [7]. Mycotoxins are non-host selective toxins produced by fungi, and more than 30 have been isolated from Alternaria. Toxins are produced by Alternaria infecting crushed and whole grains as well as fruits and vegetables [21]. These have been shown to pose a range of animal and human health risks [22]. Alternaria mycotoxins are frequently detected in fresh produce, including fruit products and juices and grains such as wheat and plant oils [23]. The species responsible for contamination are often reported to be Alternaria infectoria or A. alternata [24].

The Alternaria genus, and particularly the species A. alternata, are also of clinical signs often associated with human airway disorders, including allergy, asthma, and chronic rhinosinusitis [25]. As a result, Alternaria spp. are considered to have an enormous contribution to the 3 billion US dollars spent on relieving allergenic rhinitis each year in the USA. Alternaria spp. are also gaining recognition as human invasive pathogens. This usually occurs in immunocompromised patients, occurring as lung or sub-cutinal infections. Infection also occurs following surgery requiring antifungal treatments or further operations to remove the infection [26].

2. Alternaria spp. Characterization

2.1. Description of the Genus

The genus Alternaria was first described in 1817, with Alternaria tenuis as the type isolate. Keissler [27] found ambiguities in descriptions of A. tenuis and synonymized both A. tenuis and Torula alternata to A. alternata [28]. No sexual stage was evident in the genus, and as such, it was classified in the Phylum Fungi Imperfecti with other asexual fungi. Since the genus' conception, over 1000 Alternaria species have been described [29]. Many of these species' names are invalid as they have since been classified into other genera or because they lack type specimens. The continued revision of the genus reflects its diverse nature, possessing considerable variation in spore structure and being identified in many different ecological niches [30].

2.2. Morphological Descriptions

Most classification of the Alternaria spp. has been based on morphology [31]. This understanding was brought by published 355 essays and papers on Alternaria morphology, which was subsequently summarised in an identification guide for the Alternaria genus, re-describing 275 morphological species [32]. The Alternaria genus is characterized by large, multicellular, melanized conidia, which can possess longitudinal and transverse septae. Spores are typically broadest at the base and taper towards the end [28]. The tapering at the end of spores is commonly referred to as a "beak". Spores are often produced on conidiophores in chains that may branch or lead to secondary conidiophores that produce other spores [15]. It is mainly the individual spore characters and the sporulation patterns that are used to differentiate morphological species within the genus. Identification of Alternaria taxa has long been considered problematic. Over 1000 species have been described, and 275 names are in current use [33]

Frequent revision of groups in the genus has resulted in the species boundaries being unclear. Taxonomic keys based on morphology have been attempted but have not contained appropriate characters to identify taxa at a commonly considered species level [33]. Overlapping spore characters and natural variation in response to culturing conditions made these keys hard to follow. This was particularly true for many small-spored Alternaria spp. (including A. alternata), which display considerable morphological diversity, are present ubiquitously in the environment, and exhibit adaptation to various lifestyles, from economically essential plant pathogens to human allergens [34]. Therefore, broader groups of spore morphologies were developed to categorize these species. This "lumping" of morphologically described species did much to simplify the identification of Alternaria spp. Whether these morphological groups represent multiple distinct species or represent, a smaller number of highly variable species is still unresolved [35].

2.3. Toxin Characterisations

Concurrent to significant revisions of taxa based on Alternaria morphology, mycotoxins were being identified and characterized in Alternaria species [28]. Toxins that were associated with plant disease on major grains were of particular interest. Morphologically similar A. alternata species were found to produce toxins that conferred "host-specific" pathogenicity on fruits, vegetables, and citruses [15]. Later it was shown that these toxins had a broader host range than initially thought, leading to them being referred to as host-selective toxins (HSTs). The conflict between Alternaria morphological species descriptions and results from introduced molecular techniques has resulted in ambiguity over which morphological descriptions constitute species [35]. Multiple morphological species descriptions are available for HST producing Alternaria. Still, all these taxa possess identical DNA sequences for the internal transcribed spacer region (ITS) and have been considered a single species, A. alternata. As a result of differences of opinion in naming the HST-producers, some Alternaria pathotypes have both morphological species descriptions and pathotype designations. This has led to confusion when calling the agents of disease; for example, Alternaria mali was described as the causal agent of infection of apple trees, and the description of this species was based on spore morphology [24]. Separate from the morphological characterization of A. mali is its pathotype designation. Individuals that can produce apple HSTs are termed A. alternata apple pathotypes and were first identified in Japan. In general, current literature describes HST growing individuals as pathotypes of their host. Scientific literature and disease regulation often use the two names interchangeably, despite the name representing two different species concepts, and there is little evidence that morphological species even cause the same disease [36].

2.4. Approaches Based on Deoxyribonucleic Acid

The development of molecular approaches has advanced our understanding of evolutionary relationships in Alternaria genus [37]. Many morphological described species have been confirmed as distinct evolutionary lineages, including Alternaria brassicicola, Alternaria infectoria, Alternaria porri, and Alternaria radicina. However, in many cases, multiple morphological species are associated with a single phylogenetic lineage. These lineages generally reflect taxa that have previously been morphological species groups and have recently been described using the taxonomic level section, and subsequently in Woudenberg et al. [38]. The Alternaria section Alternaria relates to what was previously considered the "Alternaria alternata species group". This group's taxonomic status is still unresolved, as molecular approaches have shown limited resolution between morphological species [38]. Individuals within this group are generally considered to represent a single species A. alternata. This group's accurate classification is required due to its diversity of roles as an environmental saprophyte, human allergen/pathogen, and plant pathogen [39].

3. Conclusions

Host ranges of individual pathotypes within A. alternata are not yet understood; for example, pathotypes of A. alternata thought to be specific to lettuce, tomato, and strawberry have each been shown to be capable of causing leaf lesions on European pear (Pyrus communis). Furthermore, there is evidence that some European Malus and Pyrus cultivars may be less resistant to Alternaria diseases than cultivars grown inside the disease's natural host range. The European and Mediterranean Plant Protection Organisation (EPPO) lists Alternaria gaisen as a documented pest. It lists A. mali as an A1 quarantine pest, meaning that it is not present and is recommended for regulation throughout the EPPO region. Keeping in mind those mentioned above, it is essential to focus on more sophisticated methodologies in identifying Alternaria spp., especially in feed samples such as the most often consumed wheat and corn.

This article was originally published in Journal of Agronomy, Technology and Engineering Management 2020, 3(6), 499-505. http://www.fimek.edu.rs/jatem. This is an Open Access article under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

References

1. Vanwambeke, S.O.; Linard, C.; Gilbert, M. Emerging challenges of infectious diseases as a feature of land systems. Current Opinion in Environmental Sustainability 2019, 38, 31–36, doi:10.1016/j.cosust.2019.05.005.
2. Boggie, M.A.; Collins, D.P.; Donnelly, J.P.; Carleton, S.A. Land Use, anthropogenic disturbance, and riverine features drive patterns of habitat selection by a wintering waterbird in a semi-arid environment.
PLoS ONE 2018, 13, e0206222, doi:10.1371/journal.pone.0206222.
3. Puvača, N.; Bursić, V.; Petrović, A.; Vuković, G.; Cara, M.; Peulić, T.; Avantaggiato, G. Mycotoxin
Incidence of Ochratoxin A in Wine and Methods for its Control. J Agron Technol Eng Manag 2020, 3, 475–
482.
4. Cavicchioli, R.; Ripple, W.J.; Timmis, K.N.; Azam, F.; Bakken, L.R.; Baylis, M.; Behrenfeld, M.J.; Boetius,
A.; Boyd, P.W.; Classen, A.T.; et al. Scientists’ warning to humanity: microorganisms and climate change.
Nat Rev Microbiol 2019, 17, 569–586, doi:10.1038/s41579-019-0222-5.
5. Marelli, J.-P.; Guest, D.I.; Bailey, B.A.; Evans, H.C.; Brown, J.K.; Junaid, M.; Barreto, R.W.; Lisboa, D.O.;
Puig, A.S. Chocolate Under Threat from Old and New Cacao Diseases. Phytopathology® 2019, 109, 1331–
1343, doi:10.1094/PHYTO-12-18-0477-RVW.
6. Smýkal, P.; Nelson, M.; Berger, J.; Von Wettberg, E. The Impact of Genetic Changes during Crop
Domestication. Agronomy 2018, 8, 119, doi:10.3390/agronomy8070119.
7. Čolović, R.; Puvača, N.; Cheli, F.; Avantaggiato, G.; Greco, D.; Đuragić, O.; Kos, J.; Pinotti, L.
Decontamination of Mycotoxin-Contaminated Feedstuffs and Compound Feed. Toxins 2019, 11, 617, doi:10.3390/toxins11110617.
8. Johnson, E.E.; Escobar, L.E.; Zambrana-Torrelio, C. An Ecological Framework for Modeling the
Geography of Disease Transmission. Trends in Ecology & Evolution 2019, 34, 655–668, doi:10.1016/j.tree.2019.03.004.
9. Hartmann, F.E.; Rodríguez de la Vega, R.C.; Carpentier, F.; Gladieux, P.; Cornille, A.; Hood, M.E.; Giraud,
T. Understanding Adaptation, Coevolution, Host Specialization, and Mating System in Castrating AntherSmut Fungi by Combining Population and Comparative Genomics. Annu. Rev. Phytopathol. 2019, 57, 431–
457, doi:10.1146/annurev-phyto-082718-095947.
10. Pérez, L.I.; Gundel, P.E.; Zabalgogeazcoa, I.; Omacini, M. An ecological framework for understanding the roles of Epichloë endophytes on plant defenses against fungal diseases. Fungal Biology Reviews 2020, 34,
115–125, doi:10.1016/j.fbr.2020.06.001.
11. Patriarca, A. Alternaria in food products. Current Opinion in Food Science 2016, 11, 1–9, doi:10.1016/j.cofs.2016.08.007.
12. Kraus, C.; Voegele, R.T.; Fischer, M. Temporal Development of the Culturable, Endophytic Fungal
Community in Healthy Grapevine Branches and Occurrence of GTD-Associated Fungi. Microb Ecol 2019,
77, 866–876, doi:10.1007/s00248-018-1280-3.
13. Boiocchi, F.; Porcellato, D.; Limonta, L.; Picozzi, C.; Vigentini, I.; Locatelli, D.P.; Foschino, R. Insect frass in stored cereal products as a potential source of Lactobacillus sanfranciscensis for sourdough ecosystem. J
Appl Microbiol 2017, 123, 944–955, doi:10.1111/jam.13546.
14. Brambilla, A.; Sangiorgio, A. Mould growth in energy efficient buildings: Causes, health implications and strategies to mitigate the risk. Renewable and Sustainable Energy Reviews 2020, 132, 110093, doi:10.1016/j.rser.2020.110093.
15. da Cruz Cabral, L.; Rodríguez, A.; Delgado, J.; Patriarca, A. Understanding the effect of postharvest tomato temperatures on two toxigenic Alternaria spp. strains: growth, mycotoxins and cell‐wall integrity‐ related gene expression. J. Sci. Food Agric. 2019, 99, 6689–6695, doi:10.1002/jsfa.9950.
16. Tralamazza, S.M.; Piacentini, K.C.; Iwase, C.H.T.; Rocha, L. de O. Toxigenic Alternaria species: impact in cereals worldwide. Current Opinion in Food Science 2018, 23, 57–63, doi:10.1016/j.cofs.2018.05.002.
17. Schiro, G.; Verch, G.; Grimm, V.; Müller, M. Alternaria and Fusarium Fungi: Differences in Distribution and Spore Deposition in a Topographically Heterogeneous Wheat Field. JoF 2018, 4, 63, doi:10.3390/jof4020063.
18. Moretti, A.; Logrieco, A.F.; Susca, A. Mycotoxins: An Underhand Food Problem. In Mycotoxigenic Fungi;
Moretti, A., Susca, A., Eds.; Methods in Molecular Biology; Springer New York: New York, NY, 2017; Vol.
1542, pp. 3–12 ISBN 978-1-4939-6705-6.
19. Tomaš-Simin, M.; Glavaš-Trbić, D.; Petrović, M. Organic production in the Republic of Serbia: Economic aspects. Ekon: teor praks 2019, 12, 88–101, doi:10.5937/etp1903088T.
20. Barkat, E.H.; Hardy, G.E.S.J.; Ren, Y.; Calver, M.; Bayliss, K.L. Fungal contaminants of stored wheat vary between Australian states. Australasian Plant Pathol. 2016, 45, 621–628, doi:10.1007/s13313-016-0449-9.
21. Meena, M.; Zehra, A.; Dubey, M.K.; Aamir, M.; Gupta, V.K.; Upadhyay, R.S. Comparative Evaluation of
Biochemical Changes in Tomato (Lycopersicon esculentum Mill.) Infected by Alternaria alternata and Its
Toxic Metabolites (TeA, AOH, and AME). Front. Plant Sci. 2016, 7, doi:10.3389/fpls.2016.01408.
22. Puvača, N.; Ljubojevic, D.; Živkov Baloš, M.; Đuragić, O.; Bursić, V.; Vuković, G.; Prodanović, R.; Bošković,
J. Occurance of Mycotoxins and Mycotoxicosis in Poultry. CDVS 2018, 2, 165–167, doi:10.32474/CDVS.2018.02.000130.
23. Mujahid, C.; Savoy, M.-C.; Baslé, Q.; Woo, P.M.; Ee, E.C.Y.; Mottier, P.; Bessaire, T. Levels of Alternaria
Toxins in Selected Food Commodities Including Green Coffee. Toxins 2020, 12, 595, doi:10.3390/toxins12090595.
24. Scientific Opinion on the risks for animal and public health related to the presence of Alternaria toxins in feed and food. EFSA Journal, doi:10.2903/j.efsa.2011.2407.
25. Barac, A.; Ong, D.S.Y.; Jovancevic, L.; Peric, A.; Surda, P.; Tomic Spiric, V.; Rubino, S. Fungi-Induced
Upper and Lower Respiratory Tract Allergic Diseases: One Entity. Front. Microbiol. 2018, 9, 583, doi:10.3389/fmicb.2018.00583.
26. El Helou, G.; Palavecino, E.; Nunez, M. Double invasive fungal infection due to dematiaceous moulds in a renal transplant patient. BMJ Case Reports 2018, bcr-2017-222527, doi:10.1136/bcr-2017-222527.
27. Keissler, K. Zur kenntnis der pilzflora krains. Beihefte zum Botanischen Zentralblatt 1912, 29, 395–
440.
28. Eram, D.; Arthikala, M.-K.; Melappa, G.; Santoyo, G. Alternaria species: endophytic fungi as alternative sources of bioactive compounds. Italian Journal of Mycology 2018, 40-54 Pages, doi:10.6092/ISSN.2531-
7342/8468.
29. Abdel-Azeem, A.M. Taxonomy and Biodiversity of the Genus Chaetomium in Different Habitats. In
Recent Developments on Genus Chaetomium; Abdel-Azeem, A.M., Ed.; Fungal Biology; Springer
International Publishing: Cham, 2020; pp. 3–77 ISBN 978-3-030-31611-2.
30. Levetin, E.; Horner, W.E.; Scott, J.A.; Barnes, C.; Baxi, S.; Chew, G.L.; Grimes, C.; Horner, W.E.; Kennedy,
K.; Larenas-Linnemann, D.; et al. Taxonomy of Allergenic Fungi. The Journal of Allergy and Clinical
Immunology: In Practice 2016, 4, 375-385.e1, doi:10.1016/j.jaip.2015.10.012.
31. Pinto, V.E.F.; Patriarca, A. Alternaria Species and Their Associated Mycotoxins. In Mycotoxigenic Fungi;
Moretti, A., Susca, A., Eds.; Methods in Molecular Biology; Springer New York: New York, NY, 2017; Vol.
1542, pp. 13–32 ISBN 978-1-4939-6705-6.
32. Simmons, E.G. Alternaria themes and variations (151-223); 65th ed.; Mycotaxon: Ithaca, NY, 1997;
33. Somma, S.; Amatulli, M.T.; Masiello, M.; Moretti, A.; Logrieco, A.F. Alternaria species associated to wheat black point identified through a multilocus sequence approach. International Journal of Food Microbiology
2019, 293, 34–43, doi:10.1016/j.ijfoodmicro.2019.01.001.
34. De Saeger, S.; Logrieco, A. Report from the 1st MYCOKEY International Conference Global Mycotoxin
Reduction in the Food and Feed Chain Held in Ghent, Belgium, 11–14 September 2017. Toxins 2017, 9, 276, doi:10.3390/toxins9090276.
35. Armitage, A.D.; Barbara, D.J.; Harrison, R.J.; Lane, C.R.; Sreenivasaprasad, S.; Woodhall, J.W.; Clarkson,
J.P. Discrete lineages within Alternaria alternata species group: Identification using new highly variable loci and support from morphological characters. Fungal Biology 2015, 119, 994–1006, doi:10.1016/j.funbio.2015.06.012.
36. Revankar, S.G.; Sutton, D.A. Melanized Fungi in Human Disease. CMR 2010, 23, 884–928, doi:10.1128/CMR.00019-10.
37. Lawrence, A.B.; Vigors, B.; Sandøe, P. What Is so Positive about Positive Animal Welfare?—A Critical
Review of the Literature. Animals 2019, 9, 783, doi:10.3390/ani9100783.
38. Woudenberg, J.H.C.; Groenewald, J.Z.; Binder, M.; Crous, P.W. Alternaria redefined. Studies in Mycology
2013, 75, 171–212, doi:10.3114/sim0015.
39. Thomma, B.P.H.J. Alternaria spp.: from general saprophyte to specific parasite: Alternaria. Molecular Plant
Pathology 2003, 4, 225–236, doi:10.1046/j.1364-3703.2003.00173.x.