Alternaria is a fungal genus with at least 50 species. It is quite ubiquitous in the environment, and it is one of the fungi which humans interact with most frequently, on a variety of levels. Alternaria species are a leading cause of crop blight, and they also cause allergies and infections in some people and animals. Mycologists, people who specialize in the study of fungi, estimate that eventually hundreds of species in this genus will be identified, with more being added to the list of known species all the time.
These fungi are asexual, reproducing by budding and creating club-shaped spores which join together in chains to facilitate the spread of the fungus. Alternaria species are generally gray to black in color, and their colonies have a downy to woolly texture. When disturbed, a colony can break up, spreading the fungus through the air in a black cloud. This is a common problem for farmers coping with crop infestations, as removal of the infected crop inevitably releases spores of the fungus into the air, contributing to its spread. The cloud of fungus can also contribute to the development of respiratory problems.
In the natural environment, Alternaria can be found anywhere where there is cellulose, as these fungi feed on cellulose. This includes decaying plant material and living crops. The fungus also grows in homes, and it can spread via waterways. Alternaria is a very hardy fungal species, going dormant during periods of prolonged drying and quickly reemerging as soon as a water source becomes available again. The colonies also grow very rapidly, allowing the fungus to take over an area very quickly.
For farmers and gardeners, Alternaria is a concern because it can cause plant blights. When it settles in plant, it classically causes a ring of dead tissue to emerge, and this ring slowly widens and eventually kills the plant or creates an array of unsightly spots. Controlling Alternaria can be difficult because it spreads so readily, and an estimated 20% of crop damage worldwide is caused by these busy fungi.
For animals, Alternaria can cause respiratory infections and allergies, especially if they are exposed for a prolonged period of time. Fungi in this genus appear to the contribute to the development of asthma in children, and they can cause coughing and respiratory infections. In people with compromised immune systems, the fungi can also cause more serious infections of the skin, mucus membranes, and internal organs.