Pelargonium Zonate Spot Virus infecting kiwifruit plants in Italy

Pelargonium zonate spot virus (PZSV) is the single member of the Anulavirus genus (Fam. Bromoviridae) first isolated from tomato in Italy and later reported also in Spain, France, USA and Israel. Up to now PZSV has been known to naturally infect only herbaceous hosts such as tomato, pepper, artichoke and common weeds often symptomless. Symptoms on leaves and fruits of infected tomato plants are characterized by line patterns, chlorotic and necrotic rings, together with plant stunting, leaf malformation and poor fruit set, which often result in plant death as infected cells show severe cytopathological alterations. The virus is transmitted by mechanical inoculation, grafting, and through seed by means of infected pollen carried on the bodies of thrips. In May 2011 plants of kiwifruit (Actinidia chinensis) cv. Hort 16 A, exhibiting viral symptoms, were observed in two orchards in the regions of Faenza and Emilia Romagna. Symptoms include chlorotic and necrotic rings on leaves and depressed areas on the fruits with a consequent deformation of the berries. The causal agent has been successfully transmitted to indicator plants, such as Chenopodium quinoa, Nicotiana benthamiana, N. glutinosa and N. tabacum, by mechanical inoculation. Viral particles with a diameter of about 30 nm were observed on viral purification obtained from C. quinoa infected leaves. Random amplification and sequencing of nucleic acids isolated from the purified virus, led to the identification of a short segment showing high nucleotide identity with 5’ end of PZSV RNA2. RT-PCR analyses, performed using PZSV primer pair, specifically identified the virus in all indicator hosts and in leaves and fruits collected from all symptomatic kiwifruit plants. The new PZSV isolate was characterized by sequencing and by ultrastructural and immuno-transmission electron microscopy investigations. Moreover, in order to determine the effect of the virus on cellular water compartmentation, tissue metabolic activity and overall quality, fruits and leaves from infected and healthy plants were compared by NMR measurements (Proton transverse relaxation time), isothermal calo-respirometry (metabolic heat production) and visual appearance using a computer vision system.