LONG-TERM EVALUATION OF PPV INCIDENCE IN PLUM GERMPLASM AFTER ARTIFICIAL INFECTION

Sharka caused by Plum pox virus (PPV) is considered to be the main and most destructive viral disease of the genus Prunus in Central Europe. In the Czech Republic, PPV is currently widespread almost on the whole territory. All main plum growing areas are stricken by the disease and the virus severely affects the fruits of susceptible cultivars. Therefore a long-term experiment with evaluation of resistance of selected plum cultivars after artificial inoculation with PPV was established. A larger collection of plum cultivars (207 genotypes) was originally planted on Prunus cerasifera rootstock at a spacing of 6×4 m in 1990. In following years, the tested collection has been continuously supplemented with newly introduced genotypes. In 2009, 286 genotypes in all were in tests. In August 1991, all trees were inoculated with a severe strain of PPV (serotype M). From 1993 to 1995, ELISA tests were carried out for all experimental trees. The cultivars, which had negative results in ELISA tests, were reinoculated with the same strain of PPV in 1996. In the years 1998-2009, symptoms of PPV were evaluated on fruits. The highest PPV transmission occurred in the first year after infection (69.5%). The percentage of infected trees was 87.4% after reinfection in 1996. Since 1998, the spread of the disease was spontaneous and very slow. In year 2009 i.e., 18 years after artificial infection, there is still 4.8% of trees negative for PPV according to ELISA testing and 13.0% of cultivars has not developed symptoms on fruits.