Brief SummaryRead full entry
Taxonomy and Phylogeny
In 1817, Nees first described Alternaria altenata (original name is Alternaria tenuis) and established the genus Alternaria, with Alternaria alternata as the type species (Rotem, 1994). Then the dispute about its taxonomy started. In 1925, Fries described the genus Macrosporium and replaced the genus Alternaria by Macrosporium. And then, he mentioned Alternaria under the genus Torula. Finally, Fries acknowledged the exit of Alternaria (Tweedy and Powell, 1963). So, Alternaria alternata has the following synonyms: Macrosporium fasciculatum Cooke & Ellis (1817), Torula alternata Fr. (1832), Alternaria fasciculata (Cooke & Ellis) L.R. Jones & Grout (1897), and Alternaria rugosa McAlpine (1896)(Wikipedia). In 1912, it was named Alternaria alternata (Fr.) Keissl. (1912)
Alternaria alternata belongs to the following group (Wikipedia):
Species: Alternaria alternata
Alternaria alternata also belongs to Deutermycota, an artificial phylum and containing all the fungi whose sexual structure has not been observed or associated with its asexual structure.
The genus Alternaria is characteristic by the large conidia. They are produced on chains, light brown to brown, ovoid or obclavate shaped, muriform and divided by transverse and vertical walls, with or without beak at the tip. The hyphae and conidiophore are light brown and septate. The dark pigment can prevent the fungal organism from damage caused by UV-radiation (Pusz, 2009).
The species can be divided into three groups according to the number of conidia on the conidiophore: Noncatenatae with single conidia; Brevicatenatae with short chains containing three to five conidia; Longicatenatae with long chains containing 10 spores or more, and Alternaria alternata belongs to this group (Rotem, 1994).
However, the microscopic differences between Alternaria species are not significant, and the character of every species varied depending on the conditions of growth. So, the identification of species is very difficult. Generally, the maximum width of spore is from 5-13 to 6-24 nm (the mean is 9 to 17 nm), and the length of spore is from 16-37 to 35-110 nm (the mean is 37 to 69 nm). The number of transverse septa is from 0 to 23. The beak length is from 4 to 90 nm. The conidiophore length is from 20 to 300 nm (Rotem, 1994). Usually, The conidia formed in natural habitats are larger, have longer beaked tip, and are more uniform than those formed in common agar media. And, under low temperature and dry conditions, larger conidia with shorter beak are produced (Misaghi et al, 1977). On the culture, it is a grey to brown, downy or cotton colony.
Alternaria species is a hardy fungus and can live in extreme conditions. Alternaria alternata can pass the winter in the soil, seed, infected crop debris or perennial host tissue, such as bark, nodes, and scaly leaves as mycelia and or conidia. Some strains can produce survival structure, microsclerotia, to resistant the unfavorable condition.
While some Alternaria species need the stimuli to initiate the conidiophore formation and sporulation, Alternaria alternata can sporulate easily without triggering (Rotem, 1994). The spores of Alternaria alternata can be propelled into air by a shift from wetness to dryness, a rapid increase in humidity or exposure to the red light (Leach, 1975). Due to it big spores and dark pigment, Alternaria alternata can float in the air and avoid the damage from UV-radiation. So, airborne dispersal is its main dispersal method. So, it can be spread all over the world, such as North America, Africa, Europe, Asia, and Austria.
Alternaria alternata has a wide host range. Almost every host affected by Alternaria species is also affected by Alternaria alternata (Rotem, 1994). Alternaria alternata prefers to infect the senescent, heavily stressed or damaged plant tissue. On some plants, it is the secondary invader, appearing on the lesion caused by other Alternaria species (tamato). Alternaria alternata also can infect the intact and healthy plant tissue. Sometimes, it can penetrate into the flower, mycelia and conidia developing on seeds in the fruit (Halfon-Meiri and Rylski, 1983). The frequently reported plants can be infected by Alternaria alternata include: tobacco, citrus, pear, apple, wheat, tomato, bean, cotton, brassicaceae, pepper, cucurbits, potato, strawberry, and beet (Rotem, 1994).
The symptoms on the leaves are brown and circular lesions with sharply defined margin and yellow layers surrounded. Inside the lesions are many dark concentric circles like a target. With the development of disease, the lesions can develop and merge into many irregular areas. Under the favorable condition, the conidia can be seen on the lesion surface, giving the lesions a dusty appearance (Brown spot: Alternaria alternata (Fr.) Keissl).
Allergic reactions caused by fungal mold have been recognized since 1726. In the past 300 years, it is reported that many fungi can cause the allergic reactions, such as Penicillium, Chaetomium, and wheat rust (Sanchez and Bush, 2001). Deuteromycetes has been recognize to contain most of the allergenic fungi; of which Alternaria alternata is one of the most important fungi that can cause asthma and rhinitis (Bush and Prochnau, 2004). Not only the intact spores can produce and transfer the allergens, the fragmented hyphae and spores also can transfer the allergens. And, they can cause more asthma than intact spores because they can respiratory tract (Pulimood et al, 2007). And, allergy content in the spores can vary with the developmental conditions (Green et al, 2003). In the United State, almost 3.6% of the population is sensitive to Alternaria alternata in the skin test, according to a survey covered a large-scale population (Gergen et al, 1987). In the outdoor environment, the disperse of Alternaria alternata spores occurs in the dry and windy day period, usually get the peak levels in the sunny afternoon. In North America, the dispersal of spore can get the peak level in late summer and early autumn. There is no detection of Alternaria alternata spores in winter with the snow cover and colder temperature (Bush and Prochnau, 2004). In the indoor environment, Alternaria alternata spores can be found everywhere, such as the kitchen, floor, ceiling, bed, and living room. So, the asthma caused by Alternaria alternata is a big problem to human.