BIORATIONAL CONTROL METHODS FOR INSECT PESTS OF POTATO
Location: Fruit and Vegetable Insect Research
Title: First report of 'Candidatus Liberibacter solanacearum' associated with psyllid-affected carrots in Norway
Submitted to: Plant Disease
Publication Type: Research Notes
Publication Acceptance Date: November 12, 2011
Publication Date: March 9, 2012
Citation: Munyaneza, J.E., Sengoda, V.G., Sundheim, L., Meadow, R. 2012. First report of 'Candidatus Liberibacter solanacearum' associated with psyllid-affected carrots in Norway. Plant Disease. Vol 96(3):454.
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 The Norwegian Institute for Agricultural and Environmental Research in Norway, investigated whether plant pathogens may be associated with psyllid-affected carrots. It was discovered for the first time that the diseased carrots in Norway 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 Norway reduce damage caused by this important plant pathogen by effectively monitoring and controlling the carrot psyllid, which is the insect vector of the pathogen.
Carrot (Daucus carota) plants with symptoms resembling those associated with the carrot psyllid Trioza apicalis and the bacterium “Candidatus Liberibacter solanacearum” were observed in 70-80% of commercial fields and experimental plots in southeastern Norway from late July to mid-September 2011; all cultivars grown were affected, at about 10 to 100% symptomatic plants per field. Trioza apicalis, a pest of carrot in northern and central Europe, can cause up to 100% crop loss and is associated with “Ca. L. solanacearum”. Symptoms on affected plants include leaf curling, yellow and purple discoloration of leaves, stunted growth of shoots and roots, and proliferation of secondary roots. Carrot plant samples were collected from five fields in Ostfold, Vestfold, Oppland, and Hedmark Counties. Total DNA was extracted from petiole and root tissues of 27 symptomatic and asymptomatic plants each (cv. Namdal, Panther, Romance, and Yukon), with the cetyltrimethylammonium bromide (CTAB) buffer extraction method. 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 22 symptomatic plants, and a 668 bp rplJ/rplL fragment was amplified from DNA from 26 symptomatic and 5 asymptomatic plants, indicating the presence of liberibacter. No liberibacter was detected in the asymptomatic carrot plants with the primer pair OA2/OI2c. Amplicons from DNA from four carrot root samples with each primer pair were cloned (pCR2.1-TOPO; Invitrogen, Carlsbad, CA) and three clones of each of the 8 amplicons were sequenced (MCLAB, San Francisco, CA). BLAST analysis of the 16S rDNA consensus sequence from the carrot root tissues (GenBank Accession XXXX) showed 100% identity to those of “Ca. L. solanacearum” previously amplified from carrot (GU373048 and GU373049) and T. apicalis (GU477254 and GU477255) in Finland. The rplJ/rplL consensus sequence from the carrots (GenBank Accession XXXX) was 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 in Norway. 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. This plant pathogen has also been reported from carrots and T. apicalis in Finland, where it has caused serious damage to carrot crops.