EPIDEMIOLOGICAL STUDIES ON RUBUS STUNT (RS) IN BLACKBERRY ORCHARDS LOCATED NEAR TRENTO (ITALY)

Rubus stunt phytoplasma (RS), a member of the elm yellows phytoplasma group, is widespread in Rubus in continental Europe. The recent introduction of new berry cultivars in Trento province (Northern Italy) prompted us to obtain more information about the spreading of RS and other phytoplasmas in these crops. In late spring/summer 2002 field observations were carried out in different commercial berry fruit crops and in related wild species. Rubus stunt-like symptoms were observed only in few plants of Rubus spinosa cv. Topee and in almost the 43 % of plants in a blackberry crop of ‘Lochness’ located in the Adige valley. The predominant symptoms observed on these two-three years old plants have been virescence, phyllody and other severe flower and fruit anomalies. Stunted growth, short internodes, few canes, proliferation of shoots from the base and leaf reddening in early autumn were also common. RS has been reported to be spread mainly by leafhoppers (Macropsis sp.). Chromotropic traps used in the crops did not permit captures of individuals of Macropsis spp; Macrosteles cristatus, the largest leafhopper collected, was analysed. The results confirmed a strict association between the symptoms and the detection of RS phytoplasma; no other phytoplasmas were found. PCR and nested-PCR also failed to detect phytoplasmas in the symptomless plants and in all Macrosteles groups tested.
Rubus stunt is not widespread in the Trento province and Macropsis fuscula hasn’t been found; therefore vegetative propagation might have contributed to the dissemination of this pathogen. For this reason epidemiological studies are in progress, also on wild blackberries, to detect and eliminate sources of infection.