C. Marcone, L.J. Guerra, J.K. Uyemoto
doi: 10.4454/JPP.V96I1.004
Phytoplasmal diseases occur wherever peach (Prunus persica) trees are grown. However, the causal agents differ considerably in taxonomy, insect vector relationships and geographic locations. X-disease of peach is widespread in North America, but does not occur elsewhere in the world. X-disease is induced by ‘Candidatus Phytoplasma pruni’, a member of the X-disease phytoplasma group (16SrIII group, subgroup 16SrIII-A). Peach rosette, peach red suture, and peach yellows, which occur in eastern United States and Canada are all caused by the X-disease phytoplasma. Another North America disease, peach yellow leaf roll (PYLR) is present in a limited area of northern California. Its causal agent is classified in the apple proliferation (AP) group, 16SrX group, as a subtype of the pear decline phytoplasma. In Europe, phytoplasmal diseases of peach are reported under the name European stone fruit yellows and incited by ‘Ca. P. prunorum’, a member of the AP group, subgroup 16SrX-B. ‘Ca. P. prunorum’ is closely related to the PYLR agent. In Lebanon and Iran, peach trees are affected by almond witches’ broom, a lethal disease incited by ‘Ca. P. phoenicium’, a member of the 16SrIX group, subgroup 16SrIX-B. Phytoplasmas of other phylogenetic groups, known to infect a wide range of plant hosts, have been identified in declining peach trees in several fruit-growing areas of the world. The pathological relevance of several ‘nonpeach’ phytoplasmas requires further investigations as their presence was ascertained by nested PCR assays only.