A kiwifruit dieback in Verona province

An epidemic dieback of kiwifruit (Actinidia deliciosa) plants was observed in 2012 and 2013 in about 600 hectares in the prov-ince of Verona (Northern Italy). Initially, the leaves of one or more branches of the affected plants showed marginal or apical necrosis and deformation. In the later stages all leaves died and fell down and finally the plants died. Roots of intermediate diameter and distal rootlets appeared extensively rotted. The dieback began in mid-July and lasted for one or two months. The symptomatic plants were randomly distributed in patches. Phytophthora species and a Pythium strain of the vexans clade were isolated from the decayed roots purified and identified by sequence analysis of the internal transcribed spacer (ITS) region of the rDNA. RFLP analyses and/or direct sequencing performed on amplicons obtained after a nest-ed-PCR assay with the Phythopthora spp. specific primers I2/A2 and the oomycetes generic ITS4/6 primers, allowed to identify the presence of Phytophthora cryptogea in both root rot samples from symptomatic plants and in colonies isolated on agar plates from a relevant number of symptomatic plants. Experimental inoculations of young kiwifruit plants with some isolates of P. cryptogea showed typical symptoms of dieback consisting in dry leaves and secondary root decay. The soil texture and the water excess mainly related to furrow and flood irrigation appears to be the main environmental factors enhancing the epidemic outbreak. This is the first report of Phytophthora and Pythium causing an epidemic dieback of kiwifruit in Northern Italy.