Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2016
Publication Date: 1/1/2017
Citation: Tahzima, R., Massart, S., Achbani, E.H., Munyaneza, J.E., Ouvrard, D. 2017. First report of ‘Candidatus Liberibacter solanacearum’ associated with the psyllid Bactericera trigonica Hodkinson on carrots in Northern Africa. Plant Disease. 101(1):242. doi:10.1094/PDIS-07-16-0964-PDN.

Interpretive Summary: Liberibacter is a new and economically important bacterium that severely damages several crops including potato in the Americas and New Zealand and carrots in Europe. This plant pathogen is transmitted to these crops by psyllids, serious insect pests in the United States. Researchers at USDA-ARS Wapato in Washington, in collaboration with scientists at the Universite de Liege in Belgium, the National Institute for Agricultural Research in Morocco and the Natural History Museum in the United Kingdom, discovered that the psyllid Bactericera trigonica was the insect vectoring this bacterium to carrot crops in Morocco, posing a serious threat to the vegetable industry in northern Africa. Information from this research will help affected carrot producers in Africa and elsewhere reduce damage caused by this important plant pathogen by effectively monitoring and controlling its psyllid insect vectors to prevent spread of the bacterium.

Technical Abstract: Carrot plants (Daucus carota L.) exhibiting symptoms of yellowing, purpling, and curling of leaves, proliferation of shoots, formation of hairy secondary roots, and plant decline were observed in March 2014 and February 2015 in commercial fields in the Gharb region of Morocco. The symptoms resembled those caused by ‘Candidatus Liberibacter solanacearum’ infections. About 30% of the plants in each field were symptomatic and were infested with an important population of psyllids identified as Bactericera trigonica Hodkinson, reported here for the first time from Morocco. No other psyllid species have been observed in the field. Samplings were conducted to investigate whether this pathogen and the psyllid B. trigonica were associated with the observed symptoms on carrot in Morocco. A total of 100 psyllids were collected from three fields. Total DNA was extracted from individual insects using the Blood and Tissue kit and from plants using CTAB extraction method. DNA extracts were tested for ‘Ca. L. solanacearum’ by PCR using specific primer pairs Lsof/OI2c and CL514F/R to amplify a partial fragment of the 16S rDNA and rplJ/rplL 50S rDNA ribosomal protein genes, respectively. DNA samples from 35 psyllids out of one hundred and plants yielded specific bands; 1,168-bp for the 16S rDNA and 669-bp for rplJ/rplL. These results confirmed the presence of ‘Ca. L. solanacearum’ in psyllids and carrot samples collected in the Gharb Region. DNA amplicons from psyllid populations for each primer pair were sequenced. BLAST analysis of the consensus sequences for the 16S rDNA (GenBank Accession Nos. KX434610 and KX434611) showed 99% identity to ‘Ca. L. solanacearum’ from Spain and Morocco (HQ454309 and KJ740160). The two consensus sequences for the 50S rDNA ribosomal protein (GenBank Accession Nos. KX434608 and KX434609) showed 99% identity to ‘Ca. L. solanacearum’ haplotype D from Spain and Canary Island, and 100% from Morocco (JX308305, HQ454321, and KJ754507, respectively). To our knowledge, this is the first report of ‘Ca. L. solanacearum’ associated with its vector B. trigonica and carrot in Morocco and Africa. B. trigonica has caused economic damages to carrot and celery crops in the Canary Islands and mainland Spain. Another psyllid species, Bactericera cockerelli, has also caused millions of dollars in losses to potato and several other solanaceous crops in USA, Central America, and New Zealand. The presence of infested carrots and numerous economically important crops in Africa that serve as reservoirs of both Ca. L. solanacearum’ and this psyllid vector present a challenge for preventive crop disease and vector spread management.