Susceptibility of certain apricot and plumcot cultivars to plum pox virus infection.

The purpose of this research was to investigate new genetic resources for resistance to Sharka disease, which is caused by plum pox potyvirus (PPV). Sharka disease is threatening the apricot and plum industries of most European and Mediterranean countries. In apricot, PPV resistance to date has only been identified in a small number of cultivars of American origin, which have been used in Greece as parents in crosses with local cultivars. New genetic material created at the USDA/Agricultural Research Service in Fresno, California was examined for reaction to PPV after artificial inoculations by grafting and in conditions of natural virus transmission by the aphid vectors present in the field. Four trees from each of seven apricot cultivars, seven plumcots, one Pluot and one Aprium were planted at the NAGREF-Pomology Institute experimental orchard, where Sharka disease is endemic, in February 1994. All plumcot cultivars were found heavily PPV infected by the third year after planting, with very severe disease symptoms. The Aprium and Pluot also demonstrated a severe susceptibility to the disease. Among the apricots examined, only K106-2 (Robada) and 'Havecot' have escaped disease in the field.