Relative concentration of plum pox virus in leaves and flowers of some Prunus species and cultivars.

The relative concentration of plum pox virus (PPV) in leaves and flowers of plum, damson, myrobalan, blackthorn, apricot and peach trees was determined by enzyme-linked immunosorbent assay (ELISA) and expressed as the lowest dilution with positive reaction. Significant differences in relative PPV concentration were found in leaves among individual Prunus species naturally or artificially infected with the virus. The highest relative PPV concentration was found in blackthorns (7.81 x 10(-4)), common plum and apricot (1.56 x 10(-3) for the both latters). Wild growing PPV-infected plums and blackthorns can be considered equally important source of sharka infection as PPV-susceptible cultivars of plums, apricots and peaches. High PPV concentration in flowers is of diagnostical value. High variability of relative PPV concentration was observed inside the species among individual cultivars. Susceptible cultivars were characteristic by high relative PPV concentration, e.g. apricot cvs. Vegama (9.8 x 10(-5)) and Velkopavlovická (1.95 x 10(-4)), and peach cvs. Maria Emilia (7.81 x 10(-4)) and Harbinger (1.56 x 10(-3)). On the other hand, cultivars resistant to PPV were characteristic by very low relative PPV concentration, e.g. apricot cv. Stark Early Orange (5 x 10(-2)) and peach cvs. Envoy (5 x 10(-2)) and Favorita Morettini (2.5 x 10(-2)). The highest relative PPV concentration was found in young trees newly infected with PPV.