First report of curly top of Coriandrum sativum caused by beet curly top virus in the Columbia Basin of Washington State

Authors: Swisher Grimm, Kylie; CROSSLIN, JAMES - US Department Of Agriculture (USDA); Cooper, William - Rodney; FROST, KENNETH - Oregon State University; DU TOIT, LINDSEY - Washington State University; WOHLEB, CARRIE - Washington State University Extension Service

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2021
Publication Date: 4/6/2021
Citation: Swisher Grimm, K.D., Crosslin, J.C., Cooper, W.R., Frost, K.E., du Toit, L.J., Wohleb, C.H. 2021. First report of curly top of Coriandrum sativum L. caused by beet curly top virus in the Columbia Basin of Washington State. Plant Disease. 105(10):3313. https://doi.org/10.1094/PDIS-01-21-0041-PDN.
DOI: https://doi.org/10.1094/PDIS-01-21-0041-PDN

Interpretive Summary: In 2020, two fields of coriander seed crops were identified in the Columbia Basin of Washington State with leaf and stem discoloration ranging from yellow in the mildly affected plants to red and purple in the severely affected plants. In collaboration with Washington State University and Oregon State University scientists, researchers at the USDA-ARS in Prosser and Wapato, WA, were able to identify the causal agent of these symptoms as Beet curly top virus. A single beet leafhopper specimen, known to vector this pathogen to many different crops, was collected near one symptomatic coriander field and was also identified with the Beet curly top virus pathogen. Beet curly top virus has caused millions of dollars in losses to major crops within the United States, and the detection in coriander seed indicates that insect pest management strategies must be implemented to mitigate the devastating economic effects of this pathogen and its insect vector

Technical Abstract: Two fields of coriander (Coriandrum sativum) seed crops were identified in the north Columbia Basin of Washington State in July 2020 with 40 and 90% field incidence of plants showing leaf and stem discoloration ranging from yellow, in mildly affected plants, to red and purple in severely affected plants. Sweep netting along the field edges collected a single beet leafhopper (Circulifer tenellus; BLH) specimen, the known vector of the Beet curly top virus (BCTV), Beet leafhopper transmitted virescence agent (BLTVA) phytoplasma, and Spiroplasma citri pathogens which can affect a diversity of crops in Washington State, including Solanaceae and Apiaceae crops. Total nucleic acids were extracted from leaf and petiole samples of 12 coriander plants and the BLH using Dellaporta and cetyltrimethylammonium bromide extraction methods, respectively. Samples were subjected to PCR analysis to detect the BLH-transmitted pathogens which cause yellow and purple discoloration in other crops in this region. BLTVA was targeted using a species-specific nested PCR with primers P1 and P7, followed by primers FU5 and BLTVA-int; S. citri was targeted using primers P89-F and P89-R; and BCTV was targeted using curtovirus primers BCTV-2F and BCTV-2R. BLTVA and S. citri were not detected in the plants, but curtovirus was detected in 10 of 12 assayed plants. All three pathogens were detected from the single BLH. A 519 basepair region of the curtovirus capsid protein gene amplified using PCR primers BCTV2-F and BCTV2-R from seven of the infected plants and the BLH was cloned into TOP10 E.coli cells using the pCR-2.1 TOPO vector. Three clones from each sample were sequenced. For six of the seven plant samples and the BLH, three clones were identical and consensus sequences were generated. For one plant sample, two clones were identical in sequence, and the third clone contained 12 single nucleotide polymorphisms. All sequences were subjected to BLASTn analysis of the NCBI database and showed 98.3 to 99.8% identity with the BCTV sequences. Additional PCR with primers BMCTV-C1 2213F and BMCTV-C1 2609R, which target the C1 gene of the Worland strain of BCTV, detected BCTV-Worland in all plant samples and the BLH, confirming the initial results and indicating that the strain-specific primers were more sensitive than the universal curtovirus primers. BCTV infections in coriander seed crops have been observed in the Columbia Basin previously, specifically in 2002, 2005, 2008, and 2013, with significant losses incurred (up to 100%), though official reports were not made following those diagnoses by PCR. BCTV has caused millions of dollars in losses in the U.S. in major crops such as sugar beet (Beta vulgaris), tomato (Solanum lycopersicum), and pepper (Solanum annuum) (Johnson and Martin 1998). This is the first publication of BCTV affecting seed production of the specialty crop, C. sativum. The observation of symptoms at 90% incidence in one field suggests that resistant cultivars or insect pest management practices are needed to prevent significant economic impacts of BCTV on coriander seed production in this semi-arid region