RESULTS OF ELISA TESTS OF PLUM TREES ARTIFICIALLY INFECTED WITH PLUM POX VIRUS (PPV)

The next year after inoculation (1992) only the trees without any symptoms of plum pox or with non-typical ones were indexes by ELISA. From the total number of 196 trees tested, 117 were found to be infected with plum pox whereas 79 trees were free of the disease. In the following year (1993) all 446 experimental trees including those with symptoms of plum pox on leaves were indexed by ELISA. Three hundred forty-four trees positively reacted to the test and the remaining 102 trees were indicated as healthy. The trees infected with plum pox were classified into 5 groups according to their values of extinction, which were calculated by subtracting of a border value of extinction of negative samples from the actually measured extinction of every tested tree. In 1992, 21.9% of tested trees were rated into the group 1 with the lowest extinction ranging between 0.01 and 0.05 (extinction value above border value of extinction from negative controls) but in 1993 only 5.8% of tested trees could be classified into this group. On the contrary, in 1992 16.3% of trees were rated into the group 5 with the highest values of the extinction (1.01–1.5) but in 1993 as much as 36.1% of tested trees fell in that category. In both years, the tests were performed using leaves collected in September or October when the a majority of trees manifested distinct symptoms of plum pox on leaves.

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