Phytoplasma infection in peach and cherry in Italy.

A survey to verify phytoplasma presence was carried out in North-Central Italy on samples from peach and cherry orchards using the same PCR/RFLP methodology for both species. Direct and nested PCR with primers amplifying phytoplasma ribosomal or ribosomal plus spacer DNA were applied. Primers specific for different phytoplasma groups already detected in fruit trees, as well as primers amplifying a short (500 bp) ribosomal phytoplasma DNA fragment, were used to increase detection sensitivity. RFLP analysis for phytoplasma identification was then performed. Three nectarine cultivars showing some trees with delay in flowering and in fruit production were tested together with asymptomatic plants in April/May 1999. Only nested PCR with phytoplasma group specific or M1/M2 primers provided positive results. RFLP analyses identified 16SrX-A, 16SrI, and 16SrXII-A phytoplasmas. In one plant a mixed infection of 16SrI and 16SrX-A phytoplasmas was detected. No clear relationship was found among symptoms, peach variety and phytoplasma presence. The sweet cherry variety Prime Giant showed a decline shortly after plantation; in samples tested during spring and summer phytoplasmas of 16SrI-B, 16SrX-B; 16SrX-C, 16SrXII-A and 16SrIII groups were often detected therefore a relationship between cherry decline and phytoplasmas could be possible.