Alternaria alternata- An Overview


Alternaria spp are a group of Ascomycete fungi that are known for their saprophytic nature in decomposing soil and plants. They are ubiquitous, found in soil, air, and plants. They have a clinical impact as well as, it is a plant pathogen. There are over 299 species of Alternaria spp with the most commonly known species including:

  • A. alternata
  • A. botrytis
  • A. leptinellae
  • A. oudemansii
  • A. scirpinfestans

Some species are endophytic, living on plant parts such as seeds and fruits and can cause plant and fruit damage such as the mango rot. The clinical significance of some species in causing animal infections to include allergic (hypersensitivity) pneumonitis. Alternaria alternata is a causative agent of subcutaneous phaeohyphomycosis and mycotic keratitis. It is the most common species in this group of fungi.

Alternaria spp belong to the phylum Ascomycota, which is characterized by the production of sexual spores called ascospores inside a sac-like structure called an ascus. However, Alternaria spp rarely produce ascospores and instead rely on asexual spores called conidia for reproduction and dispersal. The conidia are large, dark, and multicellular, with transverse and longitudinal septa. They have a characteristic beak-like projection at the tip. The conidia are produced on branched chains of conidiophores that emerge from the hyphae.

Alternaria spp are able to grow in a wide range of environmental conditions, such as temperature, pH, moisture, and nutrient availability. They can also tolerate high levels of salt, sugar, and organic acids. They can colonize various substrates, such as plant tissues, food products, textiles, wood, and leather. They can also cause spoilage and deterioration of these materials by producing enzymes and secondary metabolites that degrade them.

Alternaria spp can also produce various toxins that have harmful effects on plants, animals, and humans. Some of these toxins include alternariol, alternariol monomethyl ether, altenuene, tenuazonic acid, and altertoxins. These toxins can cause necrosis, chlorosis, wilting, blight, rotting, and mycotoxicosis in plants. They can also cause allergic reactions, respiratory infections, skin infections, eye infections, and systemic infections in animals and humans.

Alternaria spp are important pathogens of many crops and ornamental plants worldwide. Some of the most economically important diseases caused by Alternaria spp include early blight of potato and tomato, black spot of citrus and apple, brown spot of pear and peach, leaf spot of brassica and lettuce, black rot of carrot and olive, and black mold of tomato and onion. Alternaria spp can also infect seeds and reduce their germination and viability.

Alternaria spp are also opportunistic pathogens of animals and humans, especially those with compromised immune systems or underlying diseases. They can cause infections of the skin (cutaneous), subcutaneous tissues (subcutaneous), nails (onychomycosis), sinuses (rhinosinusitis), eyes (keratitis), lungs (pneumonia), blood (septicemia), brain (meningitis), and bones (osteomyelitis). They can also cause allergic reactions such as asthma, rhinitis, conjunctivitis, dermatitis, and hypersensitivity pneumonitis.

Alternaria spp are therefore important fungi that have both beneficial and detrimental roles in nature and human society. They are widely distributed in the environment and can adapt to various conditions. They can decompose organic matter and recycle nutrients in the soil. They can also cause diseases in plants and animals that affect their health and productivity. They can also produce toxins that have various biological activities and health implications.