Reaction of an F1 apricot hybrid population to artificial and natural inoculation of Plum pox virus

The reaction to plum pox virus (PPV) inoculation is investigated in 163 F1 hybrids ‘Polonais’ x ‘Stark Early Orange’, susceptible and resistant to ‘Sharka’ disease, respectively. The hybrids are inoculated with PPV by grafting and planting in the field where the disease is endemic. Visual symptoms of ‘Sharka’ on the leaves of the hybrids are recorded eight months post-inoculation as well as in the second and fourth year. Mild disease symptoms are recorded in almost all hybrids in the first year. The ratio of hybrids presenting symptoms versus those not presenting is 9:1. This ratio changes to 1:1 in the second year and remains stable in the fourth year. The ELISA test applied to the leaves of the asymptomatic hybrids is negative, confirming the monogenic control of resistance to PPV conferred by cv. ‘Stark Early Orange’. The phenomenon of ‘recovery’ from infection accounts for the reduction in infection levels after the first year.