Atlernaria Toxins: Impacts on Plants and Animals
Authors: Pradeep Kumar, A. Kandan, J. Akhtar, Dinesh Chand1
Plant Quarantine Division, ICAR- National Bureau of Plant Genetic Resources, New Delhi-110 012
1ICAR- National Bureau of Plant Genetic Resources, Regional Station Akola, Maharastra-444 104


Alternaria genus includes various saprophytic, endophytic and pathogenic species. Alternaria toxins are phytotoxins produced by Alternaria species that cause plant diseases on cereals, fruits, oil crops, ornamentals and vegetable plants. Alternaria alternata is the most predominant Alternaria spp., and is the most important phytotoxin-producing fungus. It occurs worldwide in different habitats such as surface of buildings, cellulose, paper, textiles, soil, seeds, plant tissues etc. Due to their growth even at low temperature, Alternaria species are also responsible for spoilage of food and feed commodities during refrigerated transport and storage.

Alternaria species are capable of producing a number of host specific and non-host specific phytotoxins. Host specific phytotoxins are selectively toxic for their host plant while non-host specific can affect many plants regardless of whether they are a host or non-host of the producing pathogen. Phytotoxins often act as the initiation factor for successful pathogenesis by the production of toxins. Most of the phytotoxic metabolites acts by modifying the metabolism of the host plants, while some are toxic to the plant tissues once accumulated inside cell. Host specific toxins have role in pathogenesis while the exact roles of non specific toxins in pathogenesis are largely unknown.

Alternaria species produce more than 70 phytotoxins, but only half of them have been chemically characterised and reported to act as mycotoxins to humans and animals. The most important Alternaria mycotoxins can be grouped into three different structural classes: alternariol (AOH) and its monomethyl ether (AME) as well as altenuene (ALT), which are dibenzopyrone derivatives; tenuazonic acid (TeA), a tetramic acid derivative and altertoxins I, II and III (ATX I, II or III), which are perylene derivatives. Several phytotoxins are now known, beyond reasonable doubt, to be the determinant factor in pathogenesis.

Barley: AOH, AME, TeA
Wheat: AOH, AME, ALT, TeA
Oat: AOH, AME, TeA
Pea: AOH, AME, ALT
Tomato: AOH, AME, TeA, ALT
Apple: AOH, AME, TEN
Edible oil: AOH, AME, ALT, TeA, ATX-I, TEN
Red wine: AOH, AME

Although the acute toxicity of Alternaria mycotoxins is considered to be low in mammals, there is strong evidence that they may be mutagenic and carcinogenic (Ostry 2008). AOH, AME and ALT are not very acutely toxic but, there are several reports on the mutagenicity and genotoxicity of AOH and AME. ATXs are mutagenic in the Ames test. The presence of Alternaria mycotoxins in cereal grain has been suggested to be associated with high levels of human oesophageal cancer in China (Liu et al. 1992).The possible harmful effects of Alternaria mycotoxins are-

Cytotoxicity: can be toxic for cells
Fetotoxicity: can be poisonous to foetus
Teratogenicity: can disturb growth and development of embryo
Mutagenicity: can cause mutation
Clastogenicity: can break chromosome
Oestrogenicity: can cause estrus in animal
Tumorigenicity: can cause cancer
Genotoxicity: can damage genetic information
They can inhibit the cell proliferation

Hence, due to their possible harmful effects, Alternaria toxins are of concern for public health. So far there are limited reports in the literature of the natural contents and frequency of contamination of these mycotoxins in food and feed products. Different Alternaria spp. can be found in different habitats and geographical regions and may therefore have different metabolite profiles and toxic potential. To understand the full chemical potential of Alternaria mycotxins, it is necessary to establish a toxicological risk assessment for agricultural products for human consumption. Although there are some reports of potential risk of Alternaria mycotxin to public health, so far there are no specific international regulations for any of the Alternaria mycotoxins in food commodities. So, there is an urgent need for specific international regulations for permissible limit of Alternaria mycotoxins in food and feed commodities.

References:

1. Ostry V (2008). Alternaria mycotoxins: an overview of chemical characterization, producers, toxicity, analysis and occurrence in foodstuffs. World Mycotoxin J. 1: 175-188.

2. Liu GT, Qian YZ, Zhang P, Dong WH, Qi YM, Guo HT (1992). Etiologic role of Alternaria alternata in human esophageal cancer. Chin. Med. J. 105 (5): 394-400.



About Author / Additional Info:
Scientist, Plant Quarantine Division, ICAR- National Bureau of Plant Genetic Resources, Pusa Campus, New Delhi- 110 012