Genetic variability of AP phytoplasmas detected in the apple growing area of Trentino (North Italy).

Apple Proliferation (AP) is a phytoplasma-associated disease spread in all countries of central and southern Europe. In apple orchards of northern Italy, AP is known since 1950 but only in recent years it has become a serious epidemics and an economic problem. In 2000, Cacopsylla costalis, now C. picta, was proved to play a role as a vector of the phytoplasma in the apple growing area of Trentino by our experiments. Later, one purpose of our studies was to evaluate the genetic variability of a large number of AP isolates from naturally AP-infected apple trees and insects collected around the same region. Plant sampling involved different cultivars and rootstock-scion combinations as well as apple trees showing AP symptoms since different times. Thousands of psyllids were picked up periodically in orchards and uncultivated areas and split up by species and developmental stages. PCR-RFLP analysis was carried out for 300 samples to determine the AP subgroups. Three different RFLP profiles were found for the local AP population with very few samples belonging to AP sub-type. A correlation between AT2 type and the sub-area of origin for plant and insect samples was observed.