Comparison of different detection systems for apple proliferation phytoplasmas in Trentino (North Italy).

Severe apple proliferation epidemic is being experienced in the most important apple growing valleys of Trentino. Towards finding the resistance/tolerance to this disease, a germoplasm screening was undertaken. Reliability of available screening tests on symptomatic and asymptomatic samples was monitored. Apple samples belonging to four cultivars, were collected from six commercial orchards where the epidemic started about 15 years ago. PCR/RFLP analyses on phytoplasma 16S rRNA gene, ribosomal protein (rp) genes and nonribosomal fragment AP13/AP10 were applied and compared to serological tests carried out with ELISA using monoclonal antibodies. The asymptomatic control samples and 2 samples from symptomatic plants were negative with all the systems employed. Among the 27 positive samples with PCR/RFLP analyses on 16S rDNA and rp genes, one sample was negative in serological tests. RFLP analyses on rp genes identified the positive samples as belonging to subgroup rpX-A, on AP13/AP10 amplicons confirmed that the majority of tested samples belonged to subtype AT-2; only one sample showed the presence of AT-1 in mixed infection with AT-2 subtype