Temperature and leaf wetness affect the severity of leaf spot on lettuce and wild rocket incited by Fusarium equiseti

Eight experimental trials have been carried out under controlled conditions in order to have a better understanding of the effect of temperature and leaf wetness duration on the incidence and severity of leaf spot caused by Fusarium equiseti on lettuce cv. Elisa and wild rocket cv. Grazia. Lettuce resulted very susceptible to F. equiseti, particularly at temperatures of 25-30 A degrees C, with a higher disease index than 50% and a higher disease severity than 25%. At such temperatures, 1-3 h of leaf wetness were sufficient to cause a high disease incidence and severity, while at least 12 h of leaf wetness were necessary to cause high losses at lower temperatures. Disease incidence and severity were higher on the wild rocket at the highest temperatures (30-35 A degrees C). Only one hour of leaf wetness was sufficient to cause significant levels of disease incidence and severity at the highest temperatures, while longer periods (6-12 h) were necessary to cause significant losses at lower temperatures. The possible causes of the recent spread of F. equiseti in northern Italy on a number of crops as well as the threat represented by such a pathogen are discussed hereafter.