|Munyaneza, Joseph - Joe|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2010
Publication Date: 6/5/2010
Citation: Munyaneza, J.E., Fisher, T.W., Sengoda, V.G., Garczynski, S.F., Nissinen, A., Lemmetty, A. 2010. First Report of 'Candidatus Liberibacter solanacearum' in Carrots in Europe. Plant Disease. 94:639. Interpretive Summary: The carrot psyllid is a serious pest of carrots in northern and central Europe, where it can cause up to 100% yield loss. Mechanisms by which this insect causes damage to carrots are not understood. Researchers at USDA-ARS Wapato, in collaboration with scientists at MTT Agrifood Research in Finland, conducted studies to investigate whether plant pathogens may be associated with affected carrots. For the first time, it was discovered that the carrots affected by the psyllid were infected with a new species of the bacterium Liberibacter, recently found to severely affect potatoes and several other crops in the United States. Information from this research will help affected carrot producers in Europe and elsewhere reduce damage caused by this important plant pathogen by effectively monitoring and managing the carrot psyllid, its insect vector.
Technical Abstract: Carrot (Daucus carota) plants exhibiting symptoms that resembled those of carrot psyllid (Trioza apicalis) damage were observed in commercial fields in southern Finland in August 2008. Carrot psyllid is a serious pest of carrots in northern and central Europe, where it can cause up to 100% yield loss. Symptoms in affected plants include leaf curling, yellow and purple discoloration of leaves, stunted growth of the shoots and roots, and proliferation of secondary roots. Given recent association of liberibacter with several annual crops affected by psyllids, an investigation on whether this bacterium may be associated with the affected carrots was conducted. Total DNA was extracted from petiole tissue of 20 symptomatic and 18 asymptomatic field-collected plants, in addition to 15 plants grown from seed in an insect-free greenhouse, with CTAB buffer. DNA was also extracted from each of 10 carrot roots from plants that had been exposed to carrot psyllids in the laboratory. DNA samples were tested by PCR using primer pairs OA2/OI2c and CL514F/CL514R, which amplify a sequence from the 16S rDNA and rplJ/rplL ribosomal protein genes, respectively, of “Candidatus Liberibacter solanacearum”. DNA from 16 symptomatic and 1 asymptomatic plants yielded the expected 1,168-bp 16S rDNA amplicon whereas DNA from 19 symptomatic and 6 asymptomatic plants yielded the expected 669-bp rplJ/rplL amplicon, indicating presence of liberibacter. In addition, DNA from all the 10 root samples yielded similar amplicons with both primer pairs. Extracts from the greenhouse-grown plants yielded no products with these primers. Amplicons generated from DNA extracted from 3 petioles and 3 roots with each primer pair were cloned into pCR2.1-TOPO plasmid vectors and 3 clones of each of these amplicons were subsequently sequenced in both directions. BLAST analysis of the 16S rDNA consensus sequences from petiole and root tissues showed 99.9% identity to 16S rDNA sequences of “Ca. L. solanacearum” amplified from Capsicum annuum and Solanum lycopersicum from Mexico, and “Ca. L. psyllaurous” from potato psyllids. The rplJ/rplL consensus sequences were 97% identical to the analogous rplJ and rplL “Ca. L. solanacearum” ribosomal protein gene sequence amplified from solanaceous crops from New Zealand and to ‘Ca. Liberibacter sp.’ sequence amplified from zebra chip-affected potatoes from California. To our knowledge, this is the first report of “Ca. L. solanacearum” associated with a non-solanaceous species and outside of North and Central America and New Zealand. Diseases associated with this bacterium have caused millions of dollars in losses to several solanaceous crops.