Penicillium italicum is a common post-harvest disease and plant pathogen, causing blue mold.
Life cycle and appearance of Blue mold
Only conidia are produced by Penicillium italicum, there are no known sexual stages. The conidia survive in orchards and are dispersed by wind. The conidia infect the fruits. In most crops, infection does not become visible until the post-harvest stage. However, in some crops injured or aborting fruits may get infected during cropping. The fungus can infect the fruits through insect wounds or other damage on the fruits. It can grow at temperatures between -3 and 34 °C with an optimum between 22 and 24 °C for growth and sporulation. The fungus is closely related to Penicillium digitatum (green mould), but Penicillium italicum grows faster than Penicillium digitatum at temperatures below 10oC. At higher temperatures, Penicillium digitatum lesions expand much more rapidly than those of Penicillium italicum.
Penicillium italicum typically infects fruits and first causes a water-soaked area on the fruit skin. Subsequently, white mycelium becomes visible. In the centre of the lesion, blue to green spores are produced. The white circle around the centre is the area where sporulation has not started yet, surrounded by a water-soaked ring where the white mycelium is not visible yet.