Control strategies of Apple proliferation, a serious disease occuring both in Slovenia and in Italy

Apple proliferation (AP) is a serious disease that mainly affects apple-trees. It is caused by a phytoplasma diffused in Europe, particularly in the South. Recently, serious epidemics have been reported to occur in northern Italy, particularly on cvs Golden Delicious, Florina, Canadian Renette and Granny Smith, grafted on different rootstocks. The disease was found to be in progress also in Slovenia. Also the new genotypes resistant to scab and derived from Malus floribunda are susceptible to AP. Because of the poor quality of fruits, the infected orchards easily became economically not convenient. In Friuli-V.G., the percentage of symptomatic trees in an infected orchard can be easily over than 50%. In general, depending on the environment, cultivar and agronomic treatments the infected trees can recover from the symptoms and produce regularly. In some cases, the fruits produced by recovered trees are near to normal and of good quality. The disease has been recorded also in nurseries. In this case AP was transmitted to the young seedlings either by grafting or by natural vectors. In both cases a great and complicate problem arises. In nature the AP - agent is transmitted at least by two species of psylla (Cacopsylla costalis and C. melanoneura). AP is systemic in the host plant and it is transmitted also by grafting. The cycle of AP and of the natural vectors is roughly known. At present, we dispose of sensitive and reliable diagnostic techniques as: the use of DAPI staining, serology and molecular biology techniques. The disease is not possible to be practically cured. Preventive procedures are on the contrary possible, mainly based on the knowledge of the epidemiology of AP. The most important and general prevention measures are as follows: utilize tested material when planting new orchards; use weak rootstocks; avoid the most sensitive cvs; obtain resistant/tolerant genotypes; establish nurseries in AP-non infected areas and avoid to use propagation material derived from infected areas. When operating in an already epidemic situation: vector control by using insecticides. Roughing especially during the initial phases of the epidemiology; take advantage of recovery; use of apomytic rootstocks resistant to AP; avoid heavy pruning or pollarding; keep the plants in vegetative balance; do not replace young sensitive plants in recently rouged orchards that are placed in infected areas still during the epidemic phase of the disease.