Laboratory of Plant Viruses, Institute of Botany, Zaliuju ez eru 49, Vilnius LT-2021, Lithuania
Molecular Plant Pathology Laboratory, USDA-ARS, Beltsville, MD 20705
Alnus glutinosa (alder) is widespread in Europe and is an important component of biological diversity in natural forest ecosystems in the Baltic Region. In 2000, diseased trees of A. glutinosa exhibiting characteristically phytoplasmal disease symptoms of shoot proliferation and leaf yellowing were observed in Aukstaitija National Park, Lithuania. In other parts of Europe, alder is affected by a phytoplasmal disease known as alder yellows, which is characterized by symptoms that include yellowing and reduced leaf size, die-back of branches, and decline of trees (2,3). Proliferation of shoots has not been previously reported with this disease. An association between alder yellows and infection by a phytoplasma has been reported in A. glutinosa in Germany and Italy, and a phytoplasma has been found in A. glutinosa in France and Hungary (2,4). We examined symptomatic alder from Lithuania using nested polymerase chain reaction (PCR) (1), primed by P1/P7 and followed by R16F2n/R16R2 (F2n/R2), for amplification of phytoplasmal ribosomal (r) DNA. The results indicated the presence of a phytoplasma, designated ALY-L, in the diseased alder. We classified the ALY-L phytoplasma through restriction fragment length polymorphism (RFLP) analysis of 16S rDNA. A 1.2-kbp fragment (F2n-R2 segment) of rDNA, amplified in PCR primed by F2n/R2, was analyzed using single endonuclease enzyme digestion with AluI, MseI, KpnI, HhaI, HaeIII, HpaI, HpaII, RsaI, HinfI, TaqI, Sau3AI, BfaI, and ThaI. On the basis of collective RFLP patterns, phytoplasma ALY-L was classified as a member of group 16SrV (group V, elm yellows group), subgroup C. The amplified 16S rDNA was cloned in Escherichia coli and sequenced, and the sequence was deposited in the GenBank data library (Accession No. AY028789). Nucleotide sequence alignment revealed that 16S rDNA from phytoplasma ALY-L shared 100% sequence similarity with 16S rDNA (GenBank Accession No. Y16387) from a phytoplasma associated with alder yellows (ALY) disease in Italy. The results support the conclusion that a strain of ALY phytoplasma is present in Lithuania. Phytoplasmas belonging to groups 16SrI (aster yellows phytoplasma group) and III (X-disease phytoplasma group) have been found in herbaceous plant species in Lithuania. This report records the first finding of a group V phytoplasma, and the first finding of a phytoplasma in a tree species in the eastern Baltic Region. These findings contribute knowledge about the diversity of phytoplasmas in the Baltic Region and the distribution of ALY phytoplasma in Europe. Apparently, A. glutinosa may be infected by the phytoplasma but not develop obvious disease symptoms, as has been reported elsewhere (3). Thus, it is possible that ALY-L phytoplasma is widespread, but as yet undetected, throughout the geographic range of alder in the Baltic Region. This possibility is supported by the finding of the monophagous leafhopper vector (Oncopsis alni) of ALY phytoplasma throughout Europe (cited in Maixner and Reinert ). Further research is needed to assess the impact of phytoplasmal infections such as those by ALY-related phytoplasma strains on trends in biological diversity in the natural forest ecosystems of the Baltic Region and elsewhere in Europe.
References: (1) R. Jomantiene et al. Int. J. Syst. Bacteriol. 48:269, 1998. (2) W. Lederer and E. Seemüller. Eur. J. For. Pathol. 21:90, 1991. (3) M. Maixner and W. Reinert. Eur. J. Plant Pathol. 105:87, 1999. (4) R. Mäurer et al. Phytopathology 83:971, 1993.