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Chancre de l’abricotier : diversité bactérienne en verger

Apricot trees are affected by apricot chlorotic leafroll disease in all major cultivation areas in Europe: the disease is killing the plants few years and it widely associated with European stone fruit yellows (ESFY) ‘Candidatus Phytoplasma prunorum’ belonging to 16SrX-B. Samples from apricot trees showing typical chlorotic leafroll symptoms were collected in June/July 2010 in Serbia and Italy: 10 symptomatic and two asymptomatic plants were tested in total. In both Countries the disease was present in scattered distribution in 7 and 8 year old orchards. Phytoplasma detection was achieved by polymerase chain reaction and restriction fragment length polymorphism analyses using nested-PCR assays. Primers employed were P1/P7 followed by F1/B6 or R16F2n/R2. RFLP analyses on F1/B6 amplicons indicated the presence of 16SrXII in one of the samples from Serbia and of 16SrX-B in one of the samples from Italy. RFLP analyses with Tru1I, RsaI, HinfI, HhaI, and HpaII on R16F2n/R2 amplicons showed the presence of 16SrX-B phytoplasmas in 4 samples, two from the Italian orchard and two from the Serbian one. In the remaining three Serbian apricot samples a mixed infection of 16SrX-B and 16SrXII and a mixed infection of 16SrX-B, 16SrXII and 16SrI phytoplasmas were identified; one of the samples was negative. In two of the remaining samples from the Italian orchard a 16SrX-B and 16SrXII mixed infection was detected, while in the last sample 16SrX-B and 16SrIX-C phytoplasmas were identified. The use of nested PCR with PA2 primers on P1/P7 allow to detect 16rXII phytoplasma in the last sample from Serbia. In all the experiments carried out the two asymptomatic plants were negative. This is the first report of presence in symptomatic apricot of phytoplasmas different from ESFY, in particular the 16SrIX-C phytoplasma is reported for the fist time in this species. Work to verify the epidemic relevance of these phytoplasmas in the apricot chlorotic leafroll disease is in progress.