|Munyaneza, Joseph - Joe|
|HOMMES, M - Julius Kuhn Institute|
|WILLHAUCK, A - Julius Kuhn Institute|
|BUCK, H - Julius Kuhn Institute|
|MEADOW, R - Norwegian University Of Life Sciences|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2015
Publication Date: 8/24/2015
Citation: Munyaneza, J.E., Swisher, K.D., Hommes, M., Willhauck, A., Buck, H., Meadow, R. 2015. First Report of ‘Candidatus Liberibacter solanacearum’ Associated with Psyllid-Infested Carrots in Germany. Plant Disease. 99:1269.
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 Washington, in collaboration with scientists at Julius Kuhn Institute and The Okoring Inc. in Germany and the Norwegian University of Life Sciences in Norway, assessed whether plant pathogens were associated with diseased plants recently observed in psyllid-infested commercial carrot fields in Germany. It was discovered that the diseased carrots were infected with the pathogen causing zebra chip, a new and economically important disease of potato that has caused millions of dollars in losses to the potato industry in the United States, Mexico, Central America, and New Zealand. Information from this research will help affected carrot producers in Germany reduce damage caused by this important plant pathogen by monitoring and controlling the carrot psyllid, its insect vector.
Technical Abstract: Carrot plants with symptoms resembling those associated with the bacterium “Candidatus Liberibacter solanacearum” were observed in commercial carrot fields in Lower Saxony, Germany in September 2014. The fields were infested with the carrot psyllid Trioza apicalis and the infection rate was about 50% symptomatic plants/field. Symptoms on affected plants included leaf curling, yellow and purple discoloration of leaves, stunted growth of shoots and roots, and proliferation of secondary roots. Symptomatic carrot and psyllid samples were collected from 3 fields near Hameln. Asymptomatic carrots were also collected from an experimental field in Braunschweig and used as controls. Total nucleic acids were extracted from petiole and root tissue of 26 symptomatic and 7 asymptomatic plants, with the CTAB buffer extraction method. Nucleic acids were also extracted from 42 psyllids. DNA samples from the carrots and psyllids were tested by PCR with ‘Ca. L. solanacearum’ primers OA2/OI2c and OMB1482F/OMB2086R to amplify portions of the 16S rDNA and outer membrane (OMB) protein genes, respectively. A 1,168-bp region of 16S rDNA was amplified from 12 of the 26 symptomatic carrots. A 605-bp region of OMB protein was also amplified from these 12 symptomatic carrots, as well as one additional plant. No asymptomatic plants had amplification of the 16S rDNA or OMB protein. Ten of the 42 psyllid samples amplified both a 1,168-bp region of 16S rDNA and a 605-bp region of OMB protein. The 16S rDNA and OMB protein amplification products from 3 carrots each were cloned (pCR-2.1 TOPO, Invitrogen, Carlsbad, CA) and a total of 9 clones of the 16S rDNA and 9 clones of OMB protein were sequenced. Likewise, 16S rDNA and OMB protein amplification products from 3 psyllids were cloned and a total of 9 clones of the 16S rDNA and 6 clones of OMB protein were sequenced. A single consensus sequence for 16S rDNA was generated from the carrots (GenBank KP760076) and psyllids (GenBank KP760077). Following a blast analysis, this region showed 100% identity to a 16S rDNA sequence of ‘Ca. L. solanacearum’ haplotype C from carrots in Finland (GU373049.1). A single consensus sequence for OMB protein was also obtained from the carrots (GenBank KP760078) and psyllids (GenBank KP760079). This region showed 98% identity to OMB protein sequence of ‘Ca. L. solanacearum’ (KC768326.1) from tomato in El Salvador. To our knowledge, this is the first report of “Ca. L. solanacearum” associated with carrot and T. apicalis in Germany. T. apicalis, a pest of carrot in northern and central Europe, can cause up to 100% crop loss. Diseases associated with ‘Ca. L. solanacearum’ have caused millions of dollars in losses to potato and several other solanaceous crops in North and Central America and New Zealand. This bacterium is also associated with significant economic damage to carrot crops in the Mediterranean region and northern Africa.