Articles
SUSCEPTIBILITY OF PLUM VARIETIES TO PLUM POX DISEASE
This plantation is located at a plum pox infected region of Bulgaria.
Up to this moment, 167 local and foreign varieties have been planted there, 93 of which are already investigated and uprooted.
Twelve trees of each variety are planted (or 6 for some varieties). One of them is artificially infected by grafting infected buds on it, while the others are left to be infected in the natural way, through the plum pox virus vectors – the aphids – Brachycaudus helichrysi, Phorodon humuli and Myzodes persicae.
Each variety is recorded in terms of: the time interval elapsing between planting of the trees and their infection; the appearance of the disease symptoms both in the leaves and in the fruits, the external symptoms being taken into consideration in the latter case, as well as the symptoms on the flesh and on the stone; premature dropping of the fruits caused by the disease; some other specific symptoms displayed by the different varieties and the grade to which the trees are attacked by the aphid-vectors.
The author reports that the trees of a great many varieties show scarce symptoms of the disease during the first years following infection and consequently these varieties seem to be slightly susceptible towards the plum pox virus.
With each passing year, however, the infection in them increases more or less and they prove to be more susceptible.
Therefore, it is impossible to make a true characteristic of the susceptibility to the plum pox virus on the basis of an investigation of short duration.
The study must be carried out for at least 8–10 years after planting the trees at a constant place.
In order to make possible for the investigators in this field to compare the susceptibility of the varieties grown under the conditions of their respective countries and the strains and vectors of the plum pox virus existing there with the conditions and strains of the disease in Bulgaria and also in order to inform them about the susceptibility of some varieties widely spread in the world, the author gives more detailed information about the following varieties: Kjustendilska sinja sliva (Pozegaca), Tuleu gras, Anna Späth, De Montfort, Reine-claude verte, Admiral de Rigny, Malvasinka (Prune Pèche), Mirabelle de Nancy, Stanly, Bühler Frühzwetsche, Ontario, Reine-claude d’Althan, Graf Althan, Reine-claude violette, D’Agen, Lützelsachser, Prune d’Italie, Wangenheim, Rutgestätter and Linkoln.