|Munyaneza, Joseph - Joe|
Submitted to: Plant Disease
Publication Type: Research notes
Publication Acceptance Date: 12/11/2011
Publication Date: 3/9/2012
Citation: Munyaneza, J.E., Sengoda, V.G., Stegmark, R., Arvidsson, A.K., Anderbrant, O., Yuvaraj, J.K., Ramert, B., Nissinen, A. 2012. First report of 'Candidatus Liberibacter solanacearum' associated with psyllid-affected carrots in Sweden. Plant Disease. Vol 96(3):453. Interpretive Summary: The carrot psyllid is a serious insect pest of carrots in northern and central Europe, where it can cause up to 100% crop loss. Researchers at USDA-ARS Wapato, in collaboration with scientists at Lund University, Swedish University of Agricultural Sciences, and Findus Group Inc. in Sweden, and MTT Agrifood Research in Finland, investigated whether plant pathogens may be associated with psyllid-affected carrots. It was discovered for the first time that the diseased carrots in Sweden were infected with a 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 Sweden reduce damage caused by this important plant pathogen by effectively monitoring and controlling the carrot psyllid, which is the insect vector of the pathogen.
Technical Abstract: Carrot (Daucus carota) plants with symptoms resembling those of the carrot psyllid Trioza apicalis and “Candidatus Liberibacter solanacearum” damage were observed in 70% of commercial fields in southern Sweden in August 2011; all cultivars grown were affected, at about 1 to 45% symptomatic plants per field. Trioza apicalis, a pest of carrots in northern and central Europe, can cause up to 100% crop loss and is associated with “Ca. L. solanacearum”. Symptoms on affected plants included leaf curling, yellow and purple discoloration of leaves, stunted growth of shoots and roots, and proliferation of secondary roots. Carrot plant and psyllid samples were collected from commercial fields in the province of Halland. Total DNA was extracted from petiole and root tissues of 33 symptomatic and 16 asymptomatic plants (cv. Nevis and Florida), with the cetyltrimethylammonium bromide (CTAB) buffer extraction method. DNA was also extracted from 155 carrot psyllids. DNA samples were tested by PCR using primer pairs OA2/OI2c and CL514F/R, to amplify a portion of 16S rDNA and rplJ/rplL ribosomal protein genes, respectively, of “Ca. L. solanacearum”. A 1,168 bp 16S rDNA fragment was detected in DNA from all the 33 symptomatic and 2 asymptomatic plants, and a 668 bp rplJ/rplL fragment was amplified from DNA from all the 33 symptomatic and 4 asymptomatic plants, indicating the presence of liberibacter. DNA from 23 and 49 psyllid samples yielded similar amplicons with OA2/OI2c and CL514F/R primer pairs, respectively. Amplicons from DNA from four carrot roots and three T. apicalis with each primer pair were cloned (pCR2.1-TOPO; Invitrogen, Carlsbad, CA) and three clones of each of the 14 amplicons were sequenced (MCLAB, San Francisco, CA). BLAST analysis of the 16S rDNA consensus sequences from carrots (GenBank Accession XXXX) and T. apicalis (GenBank Accession XXXX) showed 100% identity to those of “Ca. L. solanacearum” amplified from carrots (GU373048 and GU373049) and T. apicalis (GU477254 and GU477255) from Finland. The rplJ/rplL consensus sequences from carrots (GenBank Accession XXXX) and T. apicalis (Genbank Accession XXXX) were 99% identical to the analogous rplJ/rplL “Ca. L. solanacearum” ribosomal protein gene sequences from carrots in Finland (GU373050 and GU373051). To our knowledge, this is the first report of “Ca. L. solanacearum” associated with carrot and T. apicalis in Sweden. This bacterium species has caused millions of dollars in losses to potato and several other solanaceous crops in North and Central America and New Zealand; it has also been reported from carrots in Finland.