Submitted to: Horticulture and Vegetable Growing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2005
Publication Date: 12/1/2004
Citation: Valiunas, D., Jomantiene, R., Davis, R.E. 2004. Identification of subgroup 16sri-b phytoplasma from naturally infected pear in Lithuania. Horticulture and Vegetable Growing. 23(4):29-36.
Interpretive Summary: Pear and other economically important fruit trees worldwide are seriously affected by diseases caused by phytoplasmas. In this work, we found that a phytoplasma is the apparent cause of a newly recognized pear disease, which we have named pear proliferation and decline (PPD) disease. Phytoplasmas are tiny wall-less bacteria that are transmitted from plant to plant by insects, mainly leafhoppers. Because phytoplasmas cannot be isolated and identified in pure culture in the laboratory, we used molecular methods to identify and characterize the PPD phytoplasma. We analyzed a gene, the 16S rRNA gene, which is essential for the synthesis of proteins by the phytoplasma, and discovered that the PPD phytoplasma is closely related to phytoplasmas that are classified in the aster yellows phytoplasma group. This group includes many different phytoplasma strains and has recently been named 'Candidatus Phytoplasma asteris'. This is the first work to reveal that pear can be infected by this phytoplasma species. The findings will be of interest to diagnostics laboratories, fruit growers and processors, and research scientists monitoring disease incidence and spread in fruit crops.
Technical Abstract: Diseased common pear (Pyrus communis L.) exhibiting symptoms of proliferation and decline of branches, and reduced size of leaves, was observed in a home garden in Li'kiava, district of Var'na, Lithuania. Amplification of phytoplasmal 16S rDNA confirmed infection by a phytoplasma strain, designated pear proliferation and decline (PPD) phytoplasma. Strain PPD was classified in group 16SrI (aster yellows group), subgroup B (16SrI-B), on the basis of restriction fragment length polymorphism (RFLP) analysis of the amplified phytoplasmal 16S rDNA. PPD phytoplasma is the first example of a subgroup 16SrI-B phytoplasma to be reported in pear.