Latest Research News on Alternaria: March 2021

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Latest Research News on Alternaria: March 2021

March 27, 2021 Microbiology 0

Alternaria spp.: from general saprophyte to specific parasite

Alternaria species are mainly saprophytic fungi. However, some species have acquired pathogenic capacities collectively causing disease over a broad host range. This review summarizes the knowledge on pathogenic strategies employed by the fungus to plunder the host. Furthermore, strategies employed by potential host plants in order to ward off an attack are discussed.

Taxonomy: Alternaria spp. kingdom Fungi, subkingdom Eumycotera, phylum Fungi Imperfecti (a non‐phylogenetic or artificial phylum of fungi without known sexual stages whose members may or may not be related; taxonomy does not reflect relationships), form class Hypomycetes, Form order Moniliales, form family Dematiaceae, genus Alternaria. Some species of Alternaria are the asexual anamorph of the ascomycete Pleospora while others are speculated to be anamorphs of Leptosphaeria.

Host Range: Most Alternaria species are common saprophytes that derive energy as a result of cellulytic activity and are found in a variety of habitats as ubiquitous agents of decay. Some species are plant pathogens that cause a range of economically important diseases like stem cancer, leaf blight or leaf spot on a large variety of crops. Latent infections can occur and result in post‐harvest diseases or damping‐off in case of infected seed. [1]

Clinical Importance of Alternaria Exposure in Children

The fungus Alternaria is known to be allergenic and is one of the most common fungi worldwide. We investigated the extent to which exposure to Alternaria increases the severity of asthma. We undertook a prospective cohort study in Australia of 399 school children who had positive skin tests to one or more aeroallergens. Airway responsiveness to histamine, wheeze, and bronchodilator use in 1 mo was measured five times between 1997 and 1999. Airway hyperresponsiveness was defined as PD20FEV1 = 3.9 μ mol histamine. Airborne concentrations of Alternaria spores were measured throughout the study, and mean daily concentrations over 1 mo ranged from 2.2 to 307.7 spores/m3 of ambient air. Using generalized estimating equations, we found that airway responsiveness, wheeze, and bronchodilator use increased significantly in association with increased spore concentrations and that the increase in airway responsiveness was greater in children sensitized to Alternarxia than in other children (p = 0.01). The odds ratio for airway hyperresponsiveness in children sensitized to Alternaria was 1.26 (95% CI, 1.14 to 1.39) after an increase in mean exposure of 100 spore/m3/d over 1 mo. These results suggest that Alternaria allergens contribute to severe asthma in regions where exposure to the fungus is high. [2]

Molecular systematics of citrus-associated Alternaria species

The causal agents of Alternaria brown spot of tangerines and tangerine hybrids, Alternaria leaf spot of rough lemon and Alternaria black rot of citrus historically have been referred to as Alternaria citri or A. alternata. Ten species of Alternaria recently were described among a set of isolates from leaf lesions on rough lemon (Citrus jambhiri) and tangelo (C. paradisi × C. reticulata), and none of these isolates was considered representative of A. alternata or A. citri. To test the hypothesis that these newly described morphological species are congruent with phylogenetic species, selected Alternaria brown spot and leaf spot isolates, citrus black rot isolates (post-harvest pathogens), isolates associated with healthy citrus tissue and reference species of Alternaria from noncitrus hosts were scored for sequence variation at five genomic regions and used to estimate phylogenies. These data included 432 bp from the 5′ end of the mitochondrial ribosomal large subunit (mtLSU), 365 bp from the 5′ end of the beta-tubulin gene, 464 bp of an endopolygalacturonase gene (endoPG) and 559 and 571 bp, respectively, of two anonymous genomic regions (OPA1–3 and OPA2–1). The mtLSU and beta-tubulin phylogenies clearly differentiated A. limicola, a large-spored species causing leaf spot of Mexican lime, from the small-spored isolates associated with citrus but were insufficiently variable to resolve evolutionary relationships among the small-spored isolates from citrus and other hosts. Sequence analysis of translation elongation factor alpha, calmodulin, actin, chitin synthase and 1, 3, 8-trihydroxynaphthalene reductase genes similarly failed to uncover significant variation among the small-spored isolates. Phylogenies estimated independently from endoPG, OPA1–3 and OPA2–1 data were congruent, and analysis of the combined data from these regions revealed nine clades, eight of which contained small-spored, citrus-associated isolates. Lineages inferred from analysis of the combined dataset were in general agreement with described morphospecies, however, three clades contained more than one morphological species and one morphospecies (A. citrimacularis) was polyphyletic. Citrus black rot isolates also were found to be members of more than a single lineage. The number of morphospecies associated with citrus exceeded that which could be supported under a phylogenetic species concept, and isolates in only five of nine phylogenetic lineages consistently were correlated with a specific host, disease or ecological niche on citrus. We advocate collapsing all small-spored, citrus-associated isolates of Alternaria into a single phylogenetic species, A. alternata. [3]

Evaluation of in vitro Antifungal Activity of Silver and Selenium Nanoparticles against Alternaria solani Caused Early Blight Disease on Potato

Aim: This study investigated the effect of silver and selenium nanoparticles on Alternaria solani, the pathogenic fungus causing early blight disease of potato.

Place and Duration of Study: Drug Radiation Research Department, National Centre for Radiation Research & Technology (NCRRT), Atomic Energy Authority, Cairo, Egypt, 2013.

Methodology: The fungus was isolated from infected potato leaves that showed brown circular spots as early blight disease symptoms. Silver nanoparticles (AgNPs) were prepared biologically using gamma irradiated Trichoderma viride cell free supernatant. Selenium nanoparticles (SeNPs) were prepared by glutathione method. The synthesized AgNPs were characterized by UV-Vis spectroscopy, Dynamic Light Scattering (DLS) and Transmission Electron Microscope (TEM). Kocide® fungicide was used as reference.

Results: The fungus isolated of leaf spot was identified both microscopically and genetically as Alternaria solani causing early blight disease of potato. AgNPs were spherical in shape with average size of 12.7 nm. Selenium nanoparticles were prepared by glutathione as reducing agents. Under laboratory conditions, 25 µg/ml concentration of silver nanoparticles completely inhibited A. solani as compared to Kocide®, fungicide that gave maximum inhibition at 600 µg/ml. The selenium nanoparticles completely inhibited the fungal growth at 800 µg/ml.

Conclusion: AgNPs completely inhibited the growth of A. solani at low concentrations. Silver nanoparticles might be suitable alternative to chemical fungicides. While, SeNPs can be used as antioxidant for enhancing plant immunity. [4]

In vitro Effect of Essential Oil of Peppermint (Mentha x piperita L.) on the Mycelial Growth of Alternaria alternata

Aims: The research aimed to evaluate the in vitro antifungal effect of the essential oil of peppermint (Mentha x piperita L.) in the control of Alternaria alternata.

Study Design: The experiment was conducted in a completely randomised experimental design with five treatments in four replicates each.

Place and Duration: The work was conducted at the Center of Science and Technology Agri-food of the Federal University of Campina Grande, Pombal-PB, Brazil, between February and March of 2018.

Methodology: The essential oil was added to the PDA culture medium (Potato-Dextrose-Agar) autoclaved and subsequently poured into Petri plates. The treatments comprised five concentrations of the oil (0.0, 0.4, 0.6, 0.8, and 1.0%). After the inoculation with fungi, the plates were incubated for 14 days in a B.O.D incubator at 27±2°C. With the data of mycelial diameters, the percentage of mycelial growth inhibition (PGI) and index of mycelial growth speed (IMGS) were calculated.

Results: All concentrations of peppermint oil reduced the mycelial growth of A. alternata. The minimum and maximum inhibitions occurred in the concentrations of 0.4 and 0.8%, which reached -13.27 and 72.45%, respectively. Although the maximum inhibition was 72.45%, the average percentages were 41.67 and 37.18% at the highest concentrations, showing an intermediate power of inhibition. A dose-dependent behaviour, was observed which suggests that further increases in concentration may enhance the inhibition effect of the oil.

Conclusion: The peppermint oil can be used as a viable and sustainable antifungal product in the control of this pathogen. Due to the possible dose-dependent effect, the development of studies is recommended with concentrations around 2.25% to test if the oil reaches the total inhibition. The in vivo experiments are required to verify the oil feasibility on the control of A. alternata on plants and fruits. [5]

Reference

[1] Thomma, B.P., 2003. Alternaria spp.: from general saprophyte to specific parasite. Molecular plant pathology4(4), pp.225-236.

[2] Downs, S.H., Mitakakis, T.Z., Marks, G.B., Car, N.G., Belousova, E.G., Leuppi, J.D., Xuan, W.E.I., Downie, S.R., Tobias, A. and Peat, J.K., 2001. Clinical importance of Alternaria exposure in children. American Journal of Respiratory and Critical Care Medicine164(3), pp.455-459.

[3] Peever, T.L., Su, G., Carpenter-Boggs, L. and Timmer, L.W., 2004. Molecular systematics of citrus-associated Alternaria species. Mycologia96(1), pp.119-134.

[4] Ismail, A.W.A., Sidkey, N.M., Arafa, R.A., Fathy, R.M. and El-Batal, A.I., 2016. Evaluation of in vitro antifungal activity of silver and selenium nanoparticles against Alternaria solani caused early blight disease on potato. Biotechnology Journal International, pp.1-11.

[5] França, K. R. S., Silva, T. L., Cardoso, T. A. L., Ugulino, A. L. N., Rodrigues, A. P. M. and Júnior, A. F. de M. (2018) “In vitro Effect of Essential Oil of Peppermint (Mentha x piperita L.) on the Mycelial Growth of Alternaria alternata”, Journal of Experimental Agriculture International, 26(5), pp. 1-7. doi: 10.9734/JEAI/2018/44243.

 

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