THE RECOVERY PHENOMENON IN APPLE PROLIFERATIONINFECTED APPLE TREES
L. Carraro, P. Ermacora, N. Loi, R. Osler
The presence and colonisation step of apple proliferation phytoplasma in recovered, symptomatic and never symptomatic apple trees were studied. Using serological and molecular techniques, it was demonstrated that recovered plants maintain infectivity in their roots while they lose phytoplasmas from shoots and leaves; in contrast, apple proliferation symptomatic trees are completely colonised. Several plants that showed no apple proliferation symptoms during twelve years of observation were found to be infected in their roots. Graft transmission experiments with apple proliferation phytoplasma, using both roots and buds collected from donor recovered and symptomatic trees, confirmed the results obtained by the analyses. The graft-inoculated plants did not recover and symptom severity was not influenced by the source of inoculum. To determine the health status of the apple trees as regards apple proliferation the roots must be tested.