Alternaria japonica

Alternaria japonica affects its hosts in all stages of life.[1] Infection causes a black or grey sunken lesion with a characteristic yellow border.[1][2] On the leaves of some plants, infection can cause dark, water-soaked spots.[3] The lesions can be observed anywhere on the plant.[1] In seedlings, fungal lesions on the stem are a cause of damping-off.[4] Infected seeds appear black or grey.[1]

The fungus can first be detected by visually observing symptoms on infected plants. When cultured on potato carrot agar, it will form a grey or brownish, cobweb-like mycelium.[1] Upon microscopic inspection, A. japonica has septate, branched hyphae and appears colorless to greenish grey.[1] Chlamydospores are multicellular with thick, rough walls.[1] Conidia are solitary and beakless.[1] Sequencing of the ribosomal DNA is commonly used for positive identification because the symptoms and microscopic appearance can resemble those of related species.[1][2][3][4][5]

Transmission of A. japonica occur from infected seeds and plant debris or conidia produced by the fungus in wet conditions.[1] The major hosts of this organism are species in Brassicaceae such as cauliflower, turnip, and cabbage.[1][2] Whether it can infect species outside of this family is unclear.[1] This fungus is not thought to be a cause of disease in humans, unlike other members of Alternaria.[1] Occurrences of black spot caused by A. japonica have been reported worldwide.[1][2][3][4]

Once A. japonica has been established in an area, it can be difficult to eradicate because it can survive in a dormant state in the soil for years.[1] Prevention of the spread of A. japonica by controlling the transportation of infected plant materials and seeds is crucial.[1] Disinfection of seeds is an effective preventative measure.[6] A variety of chemical fungicides can be used to protect seedlings.[1] Integrated pest management practices such as crop rotation with non-cruciferous plants can be beneficial for farmers dealing with this fungus.[1]