The psyllid Trioza apicalis Förster (Hemiptera: Triozidae) is a serious pest of carrots, Daucus carota L., in Europe. Carrots exhibiting symptoms of psyllid damage were observed in commercial fields in southern Finland in 2008. Symptoms in affected plants included leaf curling, yellow and purple discoloration of leaves, stunted growth of shoots and roots, and proliferation of secondary roots. Mechanisms by which T. apicalis induces symptoms in plants are not understood, and no plant pathogens have yet been associated with this insect. Given recent association of liberibacter with several crops affected by psyllids, an investigation on whether this bacterium is associated with T. apicalis was conducted. Polymerase chain reaction (PCR) primer pairs OA2/OI2c and LsoF/OI2c, specific for 16S rRNA gene from "Candidatus Liberibacter solanacearum," generated amplicons of 1,168 bp and 1,173 bp, respectively, from DNA extracted from field-collected psyllids (61 and 36.6%, respectively), laboratory-reared psyllids (70 and 33.3%, respectively), field-collected petioles from symptomatic carrots (80 and 55%, respectively), and laboratory-grown carrots (100% for both primer pairs). In contrast, no PCR products were detected in DNA extracted from insect-free plants. The DNA sequences of amplicons of the genes encoding liberibacter 16S rRNA from psyllids and carrots were identical. DNA of the 16S rRNA gene sequences determined from carrots and psyllids were 99.9% identical to analogous sequences of "Ca. L. solanacearum" amplified from several solanaceous crops and the psyllid Bactericera cockerelli (Sulc), a vector of this bacterium. This is the first report of a plant pathogen associated with T. apicalis and the second known psyllid species associated with "Ca. L. solanacearum".

Carrot (Daucus carota) plants with symptoms resembling those of carrot psyllid (Trioza apicalis) damage (3,4) were observed in 14 commercial fields in southern Finland in August 2008; all cultivars grown were affected at approximately 5 to 35% symptomatic plants per field. T. apicalis, a pest of carrots in northern and central Europe, can cause up to 100% crop loss (3,4). Symptoms on affected plants included leaf curling, yellow and purple discoloration of leaves, stunted growth of shoots and roots, and proliferation of secondary roots (3,4). Given recent association of liberibacter with several annual crops affected by psyllids (1,2), an investigation on whether this bacterium is associated with symptoms of psyllid damage on carrots was conducted. Total DNA was extracted from petiole tissue of 20 symptomatic and 18 asymptomatic plants (cv. Maestro, Nanda, Nipomo, Nerac, and Fontana) sampled from 10 psyllid-infested fields in southern Finland, as well as 15 plants (cv. Primecut, Cheyenne, and Triple Play) grown from seed in an insect-free greenhouse, with the cetyltrimethylammoniumbromide (CTAB) method (2). DNA was also extracted from 10 carrot roots (cv. Nantura) of plants continuously exposed to field-collected carrot psyllid colonies in the laboratory. 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 “Candidatus Liberibacter solanacearum” (1,2). A 1,168 bp 16S rDNA fragment was detected in DNA from 1 asymptomatic and 16 symptomatic plants and a 669 bp rplJ/rplL fragment was amplified from DNA from 19 symptomatic and 6 asymptomatic plants, indicating presence of liberibacter. DNA from all 10 root samples yielded similar amplicons with both primer pairs. DNA from all the greenhouse carrot plants yielded no amplicon. Amplicons from DNA from three petioles and three roots with each primer pair were cloned (pCR2.1-TOPO; Invitrogen, Carlsbad, CA) and three clones of each of the 12 amplicons were sequenced (MCLAB, San Francisco, CA). BLAST analysis of the 16S rDNA consensus sequences from petiole and root tissues (GenBank Accession Nos. GU373049 and GU373048, respectively) showed 99.9% identity to those of “Ca. L. solanacearum” amplified from Capsicum annuum (FJ957896) and Solanum lycopersicum (FJ957897) from Mexico, and “Ca. L. psyllaurous” from potato psyllids (EU812559). The rplJ/rplL consensus sequences from petioles and roots (GenBank Accession Nos. GU373051 and GU373050, respectively) were 97.9% identical to the analogous rplJ/rplL “Ca. L. solanacearum” ribosomal protein gene sequence from solanaceous crops in New Zealand (EU834131) and to “Ca. Liberibacter” sp. sequence from zebra chip-affected potatoes in California (FJ498803). To our knowledge, this is the first report of “Ca. L. solanacearum” associated with a nonsolanaceous species and the first report of this pathogen outside of North and Central America and New Zealand (1,2). References: (1) L. W. Liefting et al. Plant Dis. 93:208, 2009. (2) J. E. Munyaneza et al. Plant Dis. 93:552, 2009. (3) G. Nehlin et al. J. Chem. Ecol. 20:771, 1994. (4) A. Nissinen et al. Entomol. Exp. Appl. 125:277, 2007.

Carrot psyllid, Trioza apicalis, is a serious pest of carrot in Northern Europe, as it can significantly damage young carrot seedlings in a period as short as 3 days. This study was conducted to investigate effects of carrot psyllid feeding at different plant growth stages on carrot yield and to assess changes in content of sugars, phenolics and related compounds in carrot roots resulting from the psyllid feeding. In addition, reflectance of carrot leaves was measured to assess the intensity of discolouration in damaged leaves. Results showed that carrot yield was significantly reduced by a 3-day carrot psyllid feeding period when the seedlings were exposed to psyllids at 1-or 2-leaf stage. However, at 4-leaf stage feeding by one carrot psyllid did not reduce yield. Sucrose concentration in the damaged roots was significantly decreased, whereas concentrations of some phenolic compounds were significantly increased. The reflectance of leaves of damaged carrots differed significantly from those of undamaged control leaves. These observations indicate that carrot psyllid damage has potential to lower not only the carrot yield, but also the carrot crop quality. No phytoplasma was detected in the carrots exposed to psyllids, but recently, T. apicalis has been associated with 'Candidatus Liberibacter solanacearum'. The role of carrot psyllid feeding and the psyllid-associated bacterium in the damage formation are discussed.A.I. Nissinen et al.Carrot psyllid feeding: yield, sugars and phenolics

Carrot (Daucus carota) plants with symptoms resembling those associated with the carrot psyllid Trioza apicalis and the bacterium “Candidatus Liberibacter solanacearum” (1–4) were observed in 70% of commercial fields in southern Sweden in August 2011, with approximately 1 to 45% symptomatic plants per field. T. apicalis, a pest of carrot in northern and central Europe, including Sweden, can cause as much as 100% crop loss and is associated with “Ca. L. solanacearum” (1–4). Symptoms on affected plants include leaf curling, yellow and purple discoloration of leaves, stunted growth of shoots and roots, and proliferation of secondary roots (3). Carrot plant and psyllid samples were collected from fields in the province of Halland. Total DNA was extracted from petiole and root tissues of 33 symptomatic and 16 asymptomatic plants (cvs. Nevis and Florida), with the cetyltrimethylammonium bromide (CTAB) buffer extraction method (2,3). DNA was also extracted from 155 psyllids (3). DNA samples were tested by PCR using primer pairs OA2/OI2c (5′'-GCGCTTATTTTTAATAGGAGCGGCA-3′/5′-GCCTCGCGACTTCGCAACCCAT-3′) and CL514F/R (5′-CTCTAAGATTTCGGTTGGTT-3′/5′-TATATCTATCGTTGCACCAG-3′), to amplify a portion of 16S rDNA and rplJ/rplL ribosomal protein genes, respectively, of “Ca. L. solanacearum” (2,3). A 1,168-bp 16S rDNA fragment was detected in the DNA from all 33 symptomatic and two asymptomatic plants, and a 668-bp rplJ/rplL fragment was amplified from the DNA of all 33 symptomatic and four 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 the DNA of 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 carrot (GenBank Accession No. JN863095) and T. apicalis (GenBank Accession No. NJ863096) showed 100% identity to those of “Ca. L. solanacearum” previously amplified from carrot (GU373048 and GU373049) and T. apicalis (GU477254 and GU477255) from Finland (2,3). The rplJ/rplL consensus sequences from carrot (GenBank Accession No. JN863093) and T. apicalis (GenBank Accession No. JN863094) were 99% identical to the sequences of rplJ/rplL “Ca. L. solanacearum” ribosomal protein gene 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. The disease associated with this bacterium caused millions of dollars in losses to potato and several other solanaceous crops in North and Central America and New Zealand (1). This plant pathogen is also associated with significant economic damage to carrot crops observed in Finland (2,3). References: (1) J. E. Munyaneza. Southwest. Entomol. 35:471, 2010. (2) J. E. Munyaneza et al. Plant Dis. 94:639, 2010. (3) J. E. Munyaneza et al. J. Econ. Entomol. 103:1060, 2010. (4) A. Nissinen et al. Entomol. Exp. Appl. 125:277, 2007.

Occurrence of 'Candidatus Liberibacter solanacearum' (CLso) was studied in field-grown carrots (Daucus carota) in different regions of Finland. In addition, the frequency of CLso in carrots and in field populations of its vector, the carrot psyllid (Trioza apicalis), was studied in southwestern Finland. CLso was detected in six of the seven regions where the main carrot cultivation areas are located. The highest disease incidence was found in southwestern Finland, in the area where this carrot pathogen was originally found. In the Tavastia Proper and Southwest Finland regions, CLso was detected in 26 out of 30 randomly chosen fields inspected in 2013 and 2014, and in a third of those fields more than 10% of plants showed symptoms. Of those carrots showing both psyllid feeding-associated leaf curling and CLso infection-associated leaf discolouration symptoms, 77% were CLso positive in the PCR test. Some symptomless carrots from the affected fields also tested positive. Of the carrot psyllid individuals collected from the same area, 60% were CLso positive. Elsewhere, disease incidence was variable in South Ostrobothnia in western Finland and low but established in South Savonia in eastern Finland. CLso was not detected in the North Ostrobothnia region. Sequencing of the amplified DNA fragments confirmed that the bacteria in the carrot samples from different areas within Finland all represented CLso haplotype C. The frequent occurrence and wide distribution of this pathogen, transmitted by a psyllid that does not migrate over long distances, suggest that it is persistent in Finland.