SPREAD OF PLUM POX VIRUS IN NEW PLUM ORCHARDS OF THE CZECH REPUBLIC AND CULTIVAR RESISTANCE

A majority of the territory of the Czech Republic is infested by plum pox.
Trees in plum orchards, which were established by using virus-free planting material, were contaminated by plum pox at a rate fluctuating from 0 to 3% per year in a dependence on infection pressure of the pathogen from surrounding.
If a part of the planted trees was already infected, the rate of plum pox spreading was much higher.
The most dangerous is the source of the infection that is located less than 30 m from the healthy trees.
The closer is the distance the greater is the risk of every new infection.
Trees of ‘Domestic Prune’, that is very susceptible to PPV, are more frequently infected in cases of direct contacts with infected trees than trees of other cultivars.
In some years the spread rate of the disease was up to more than three times higher than the other years.
A plum tree is the most susceptible to PPV infection in its age of three years.
A resistance of the rootstock to PPV does not generate any greater protection for grafted cultivars.
Trees on less vigorous rootstocks were less infected than trees on more vigorous rootstocks.
Every newly infected tree becomes very soon a source of the next infection for all neighboring trees.
This fact also highlights the significance of timely grubbing of affected trees immediately after an emergence of symptoms of this viral disease.
The highest level of resistance to PPV was found in ‘Bila Trnecka’, ‘Francia Naranes’, ‘Large Sugar Prune’, ‘Reine Claude Diaphane’, ‘Renkloda Jandacek’ and one seedling.