Evaluation of cherry cultivars for their response to infection by Plum pox virus sweet cherry strain

Starting in 1994, when Plum pox virus (PPV) was recovered for the first time from naturally infected sweet and sour cherry trees in Italy and Moldova respectively, the virus has been found in cherry in different countries of eastern Europe, such as Hungary, Bulgary, Romania and Czech Republic. Due to the many recoveries of PPV-cherry isolates in commercial orchards, it is interesting to evaluate the degree of receptivity of different cherry rootstocks and commercial varieties. At the aim two different experiments were carried out. During March 2000, one-year-old scions of 35 cultivars of sweet and sour cherry grafted on Prunus mahaleb plants were chip-budded in 5 replicas, using 5 chips per scion, with PPVSwC isolate from artificially infected P. avium plants. Plants were grown in insect proof screen in a greenhouse, and monitored for symptoms appearance. They were assayed after 2 months in 2000 and soon after the re-growth in years 2001, 2002 and 2003, by RT-PCR using the primer pair described by Wetzel et al. (1991). The second experiment started in March 2003. Five replicas of micro-propagated seedlings of 20 different cherry rootstocks and commercial varieties were mechanically inoculated with PPV-SwC from infected Nicotiana benthamiana. Local and systemic symptoms appearance was surveyed, and ELISA was performed using the PPV-SwC specific monoclonal antibody MabAC (Myrta et al., 2000) on inoculated and not inoculated leaves, respectively 4, 10 and 15 weeks post inoculation. Systemic infection by PPV-SwC was confirmed by RT-PCR performed as above. Plants resulted infected by PPV-SwC both when chip-budding and when mechanical inoculation were used for transmission. The degree of receptivity was depending on the different cherry species and cultivar tested.