New or re-emerging fungal Citrus diseases in the Mediterranean

Autori: Francesco Maria Grasso, Patrizia Bella, Salvatore Grasso and Antonino Catara

In recent years, the spread to new Mediterranean areas of citriculture with its new cultural practices, new citrus varieties and a changing climate, has led to the need to cope with new or reemerging fungal plant diseases. The most notable are ‘greasy spot’ and ‘alternaria spot’. A few papers have been published on this topic, but little attention has been given to them. For the last five years, many Italian orchards have been conspicuously dropping mature leaves affected with greasy spot to their undersides, which may develop groups of peritecia carrying asci which are morphologically similar to the Mycosphaerella genus. Potato agar cultures of the  symptomatic mesophyll slowly grow greenish-brown colonies, bearing erratically multiseptate conidia, similar to the genus Cercospora. Some citrus species are more susceptible and may require appropriate spraying once the biological cycle of the fungus is defined. Only one out of four Alternaria diseases occurs frequently – the mandarin Alternaria brown spot, which is becoming more and more diffuse in many cultivars in Italy and Spain, damaging the leaves and fruit of mandarin hybrids despite frequent chemical spraying. Septoria spot is less common in Sicily and Calabria, where symptoms occur on the fruit and leaves of lemon and bergamot. Anthracnose is an old disease affecting citrus twigs, leaves and fruit and is caused by a primary fungus coloniser of injured and senescent tissue in the field and usually does not require spraying.

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