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Alternaria dianthi
Alternaria dianthi, sometimes known as carnation blight, is a fungal pathogen of the genus Dianthus.[1] Alternaria dianthi infections begin as small circular or ovular spots on leaves and stems, which can be red, purple, brown, yellow or gray.[2] This pathogen has been found in carnation and other Dianthus cultures worldwide, including in India,[3] the United States,[1] New Zealand,[4] the Canary Islands,[5] and Egypt.[6] Fourteen gene sequences of Alternaria dianthi have been published as of April 11, 2014[7] SymptomsAlternaria dianthi can infect healthy plants, and favors humid, warm environments.[1] The multicolored circular spots can grow to infect entire plants, resulting in wilting or death.[2] These spots tend to be smaller than one centimeter, but can be larger, especially around stems.[5] The cankers formed by A. dianthi spread through the stomata of leaf cells, and generally lead to yellowing, wilting, and death of the leaves of infected plants.[8] Life cycleAlternaria dianthi reproduces asexually, forming row-like spores off of hyphae. Spores are formed on blisters on the host as well as within the mycelium. The thin, globular spores are spread through water.[9] Spore production and infection decreases over winter, and has been observed to be highest in rainy summer months.[10] The spores of A. dianthi germinate optimally around 24 °C (75 °F), and cannot germinate below 4 °C (40 °F) or above 32 °C (90 °F).[1] The fungus has been cultured on simple media such as potato dextrose agar, and does not need Dianthus tissue to germinate.[2][5] Spores come into contact with healthy leaf and stem tissue of Dianthus plants through wind, rain, and contact with infected tissue.[8] The host plant must be wet or moist for spores to germinate.[8] Moderate to high humidity is also a requirement,[1] and one study found that spores would not germinate under 55% humidity.[5] The life cycle takes about four days from germination to the production of new conidia.[5] Spores produced by Alternaria species are black, and can persist on dead tissue, in soil, and on hard surfaces such as those found in greenhouses.[11] No observations of pathogens of Alternaria dianthi have been published.[citation needed] ImpactAlternaria dianthi was first recorded in the scientific literature by F.L. Stevens and J.G. Hall in 1909, from florists in the United States.[9] The fungus, along with other members of the genus Alternaria, is effectively controlled by the commercial fungicide mancozeb,[8] as well as dithiocarbamates, chlorothalonil, and iprodione.[11] Although A. dianthi has been found in wild and commercial varieties of Dianthus plants worldwide, no studies of the economic impacts or losses due to the disease have been published.[citation needed] References
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