Investigations of new viral pathogens on actinidia spp.

Kiwifruit is an important horticultural crop originated from China. More than 50 species are recognized in the genus Actinidia but in New Zealand and Italy A. deliciosa and A.chinensis are the mostly widely grown cultivars.Kiwifruit has been considered relatively disease free for more than 30 years however, since 2003, several viruses and virus-like diseases have been identified and more recent studies demonstrated that Actinidia spp. can be infected by a wide range of pathogens. Currently 13 different viral species have been identified on kiwifruit plants and these were divided into 3 groups: non-specialistic viruses, kiwifruit adapted viruses and viruses inducing diseases. The last group of viruses induces diseases in kiwifruit and to date only 2 viruses have caused significant damage to kiwifruit within commercial orchards. In N.Z. cherry leaf roll virus has been detected on kiwifruit associated with symptoms including leaf spots, fruit malformation, reduction in yield, bark cracking and cane wilting. Pelargonium zonate spot virus has been detected in Italy associated with severe symptoms on leaves and fruits. Infected plants showed chlorotic and necrotic rings on leaves and depressed areas on the fruits that resulted in deformation of the berries. Moreover, kiwifruit plants showing symptoms attributable to viral infection such as leaf narrowing and curling and wood pitting, have been recently identified during inspections of commercial orchards but none of the known kiwifruit-infecting viruses were identified. Unidentified filamentous viral particles were detected in all these symptomatic samples. The identification of at least 13 viruses that can infect kiwifruit has important repercussions for orchard managment, especially for nurseries that propagate kiwifruit.