EFFECT OF PRUNUS NECROTIC RINGSPOT VIRUS (PNRV) AND PRUNE DWARF VIRUS (PDV) ON SOME BIOLOGICAL PROPERTIES OF PEACH*

The results from several years of observations indicated that the PNRV isolates did not display visible symptoms on the leaves but twig and branch withering was induced as well as death of whole trees. The trees infected with N₁ and N₃ reacted with symptoms typical for PDV.

Isolates C_13–11, H_7–2 and N₃ indicated decrease of the leaf and flower buds as well as the nodes of the infected trees by 66–96%. Leaf size was decreased by 14–80%. The trunk and limb circumference of the trees infected with H_7–2 and N₃ isolates was decreased, too (42–71%). Analogical were the results for length of the limbs and the annual growth (54–72%). The death of the trees infected with the two viruses was up to 80%.

PNRV and PDV had a negative effect on the fruit set, fruit size and number, and yields (37–99%) of the infected trees. The plastic pigments in the leaves of the infected trees were decreased within the limits of 20–59%. The chemical constituents of the fruits of the infected trees were variable during the different years of investigation.