Are phytoplasmas involved in a severe peach decline?

During surveys performed from 2001 to 2003 in peach orchards a severe decline of trees was observed. Leaf symptoms start in early summer and in one to two weeks the plants dry up and die. Percentages of affected plants varied according to cultivars and years. To verify phytoplasma presence after exclusion of other pathogens by visual inspections and laboratory tests, nucleic acids were extracted, and nested PCR/restriction fragment length polymorphism (RFLP) analyses were employed. The presence of phytoplasma specific DNA bands was observed in some of the symptomatic samples examined. RFLP patterns of sequences amplified from symptomatic peach showed the presence of profiles referable to three different phytoplasmas belonging respectively to elm yellows, aster yellows and stolbur groups. In particular 16SrV-B (Ca. Phytoplasma ziziphi), and 16SrXII-A phytoplasma (Ca. Phytoplasma solani) subgroups were identified in samples from northern Italy. Phytoplasmas belonging to 16SrXII-A subgroup were also identified in the roots of one symptomatic peach tree from Chile. From sequencing data of the 16S rDNA region of 16SrV-B phytoplasmas, a 97% similarity was found with strains recently described as associated with peach and nectarine decline in India. These latter phytoplasmas were only detected in symptomatic young branches of one plant in the middle of spring, and in the phloem of the same plant aster yellows phytoplasmas (16Sr-B) were identified. In plants showing similar symptoms, stolbur phytoplasmas were identified in samples collected in summer. Other samples from different symptomatic plants or from asymptomatic plants collected in the fields where the disease was studied in Italy and in Chile were negative to the molecular tests.