Alternaria dianthi

Alternaria 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. Spore production and infection decreases over winter, and has been observed to be highest in rainy summer months. 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). The fungus has been cultured on simple media such as potato dextrose agar, and does not need Dianthus tissue to germinate. Spores come into contact with healthy leaf and stem tissue of Dianthus plants through wind, rain, and contact with infected tissue. The host plant must be wet or moist for spores to germinate. Moderate to high humidity is also a requirement, and one study found that spores would not germinate under 55% humidity. The life cycle takes about four days from germination to the production of new conidia. 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. No observations of pathogens of Alternaria dianthi have been published.