Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2000
Publication Date: N/A
Interpretive Summary: Clover (Trifolium spp.) is a crop important for animal consumption in many areas of the world. For more than twenty years, diseases of clover attributed to phytoplasma infections have been reported in different regions of Europe, but little is known about the identities of the phytoplasmas that may be causally associated with these diseases. In this paper, we describe the detection and identification of two phytoplasmas as the probable causes of diseases that induce severe symptoms in clover in Lithuania. In the disease known as clover phyllody, we have identified a phytoplasma which we have termed clover phyllody phytoplasma-Lithuania, and in a disease known as clover dwarf, we have identified both clover phyllody-Lithuania phytoplasma and a phytoplasma related to clover yellow edge phytoplasma. Detection and identification of these phytoplasmas were accomplished through the use of polymerase chain reactions, RFLP analyses, and determination of nucleotide sequences of 16S rRNA genes. The findings extend the known geographical ranges of these phytoplasma pathogens and point to the possible synergistic interaction of two phytoplasma taxa. They will be of interest in scientists and regulatory agencies in the United States and other countries in their efforts to understand plant diseases and to reduce or prevent their spread.
Naturally diseased plants of clover (Trifolium spp.) exhibiting sumptoms of clover phyllody disease (virescence and phyllody of flowers) or of clover dwarf (abnormally small leaves, shortened internodes, proliferation of shoots, and dwarf growth habit) were observed in the field in Lithuania. Phytoplasma group-specific PCRs and RFLP analysis of 16S rDNA revealed that tthe plants were infected by two mutually distinct phytoplasmas. Clover phyllody diseased plants were infected by a subgroup 16SrI-C phytoplasma (CPh-L) related to clover phyllody (CPh-C) phytoplasma in Canada. Clover dwarf diseased plants were infected by both CPh-L and a phytoplasma (CYE-L) related to clover yellow edge (CYE-C) phytoplasma (subgroup 16SrIII-B) in Canada. A 1.8 kbp fragment of rRNA operon from CYE-L was amplified, cloned, and sequenced, and putative restriction sites mapped. Since this sequence shared high similarity (99.7%) with that of CYE-C and exhibited no odifferences from CYE-C in RFLP patterns of 16S rDNA, we tentatively classifed CYE-L in subgroup 16SrIII-B (type strain, CYE = CYE-C phytoplasma) of Prunus X-disease phytoplasma group. These findings extend the known geographical ranges of subgroup I-C and subgroup III-B taxa to the region of northern Europe including Lithuania, and they point to the possible synergistic interaction of two phytoplasms taxa.