First report of Fusarium semitectum as the agent of twig cankers on Persian (English) walnut in Italy.
English (Persian) walnut (Juglans regia) is the most widely cultivated walnut species. During the last ten years, the increment of walnut cultivation in Italy has been accompanied by changes in cultural management. Changes were addressed to develop highly specialized cultivations with intensive pruning, fertilizer application, irrigation and chemical treatments. For these reasons, more consideration has been given to the sanitary situation, in particular since 1998 when brown apical necrosis (BAN) was first observed. BAN is a fungal complex disease causing fruit drop, in which several Fusarium spp. are involved, among which Fusarium semitectum [F. incarnatum] represents one of the major causal agents. From 2005 onward, investigations on sources of inoculum for BAN led to observing the presence of twig cankers on walnut cv. Lara trees located in northern Italy (Povalley). Cankers observed in late spring to summer were usually small (1-3 cm long) and mainly occurred on the new growth strongly incited by intensive pruning. Pale orange sporodochia were evident on lesions. Based on morphological observations, sequence analyses and pathogenicity tests, the causal agent was identified as F. semitectum. This is thought to be the first report of F. semitectum causing twig cankers on walnut in Italy. This pathogen was already reported as an agent of canker on walnut in Argentina.