A NEW DISEASE: LEADER DIE-BACK IN ACTINIDIA CHINENSIS 'HORT16A' IN ITALY

A new disease affecting Actinidia chinensis 'Hort16A' (ZESPRI™ GOLD) vines, observed as a leader die-back, appeared for the first time in one orchard in Italy in October 2004. In April 2005, the same symptoms were found in many plants in the same orchard and in other ‘Hort16A’ orchards in the Latina area (Latium, Italy). The first symptoms of the disease appeared to be lack of budburst due to death of single canes or, more often, entire leaders. In most cases the affected leaders and/or dead canes became swollen and the bark cracked at the site of infection. When the bark was removed, streaky brown lesions were observed in the wood below. The lesions appeared to cause localised blockage of the xylem resulting in the death of infected parts of the vine. Lesions most often occurred in association with unprotected old pruning wounds suggesting these wounds could be the main point of entry for infections. Several fungal species have been isolated from lesions, with Cadophora spp. being the most common. The identification and importance of these fungi are discussed. Fruit with beak-end shrivelling were found in some orchards in 2004 including one with the leader die-back disorder, and it is possible that this shrivelling is an early symptom of leader die-back. The increasing number of orchards with plants infected suggests a high potential for infection with this new disease. In addition, vines affected were established in 2001 and 2002, so it is a relatively virulent infection on young vines. Control measures such as removal of infected leaders and canes from vines, wound protection, and orchard practices to reduce the risk of reinfection are discussed.