Testing of plum germplasm for sensitivity to plum pox.

A long-term orchard experiment with a broad assortment of plum cultivars aimed to screen their sensitivity to plum pox virus (PPV) was established in 1991. For this purpose, 207 cultivars to be artificially infected with PPV at a permanent site were chosen. The serotype M of PPV from a tree of cv. Domestic Prune, which had not been contaminated by other viruses, was used as a source of the infection. Three buds infected with PPV were budded on 1-year-old trees. In the course of experiment the following results were obtained. The highest transmission of PPV was recorded in the first year after infection, when 69.5% of positive trees were detected by enzyme-linked immunosorbent assay (ELISA). After 4 years, the absence of PPV was still detected in 11.2% of the cultivars. These were reinfected with the same source of PPV in 1996. In 1998, there were 92.9% of trees contaminated by sharka. Seven years after infection with PPV, a dieback of 41 trees took place. In the most cases a presence of an ilarvirus in the plant was detected. The PPV infection was not transferred further on cvs Bila trnecka, Francia Naranes, Large Sugar Prune, Reine Claude Diaphane, Renkloda Jandacek, Scoldus, Tarnina x Kirke, Valasska trnecka and K-4. There were 75% of trees fruited in 1997. Only 28 cultivars had no symptoms of PPV on fruits. A statistically significant relationship between the incidence of PPV after the artificial infection and a the presence of prunus necrotic ring spot virus (PNRSV). The presence of PNRSV reduced the transmission of PPV. Relationships between PPV and prune dwarf virus (PDV), and between PPV and (PDV + PNRSV) were not statistically significant.