Horizontal Spread of Ilarviruses in Young Trees of Several Peach Cultivars

Natural spread of Prune dwarf virus (PDV) and Prunus necrotic ring-spot virus (PNRSV) was monitored among healthy trees of six peach (Prunus persica (L.) Batsch) cultivars interplanted into a mature peach orchard between virus-infected trees of the cultivar Carson. Spread of PDV to a few trees of cvs. Andross, Carson, and Halford occurred during bloom just after the dormant test trees were planted in the orchard, as indicated by serological and biological assays during the next season. In contrast, virus infections in cvs. Dr. Davis, Loadel, and Ross were not detected until the fourth to sixth growing seasons. By the seventh season, cumulative transmissions for PDV and PNRSV were 41 and 9, respectively, which included double virus infections in five test trees. Significant differences in cumulative transmission of PDV but not of PNRSV occurred by the fourth season (P = 0.0020). Overall, virus infections among the six cultivars ranged from 70 to 100%.