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Authors Swisher Grimm

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Swisher Grimm, Kylie


Publications
2

CitationNamesAbstract
First report of ‘ Candidatus Phytoplasma trifolii’ and Spiroplasma citri in Cannabis sativa in Washington State, USA Wagstaff et al. (2026). Plant Disease Ca. Phytoplasma trifolii
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Development of a Loop-Mediated Isothermal Amplification (LAMP) Method to Detect the Potato Zebra Chip Pathogen ‘Candidatus Liberibacter solanacearum’ (Lso) and Differentiate Haplotypes A and B Jiang et al. (2023). Plant Disease 107 (6) “Liberibacter solanacearum”
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First report of ‘ Candidatus Phytoplasma trifolii’ and Spiroplasma citri in Cannabis sativa in Washington State, USA
In 2022 and 2024, field surveys were conducted in the Columbia Basin of Washington State, USA, for pathogens transmitted by the beet leafhopper, Circulifer tenellus, including beet curly top virus (BCTV), ‘Candidatus Phytoplasma trifolii’ (CPt), and Spiroplasma citri (S. citri). For these pathogens, an association of symptoms with a causal agent is often complicated by co-infections and the inability to culture CPt (Hu 2021; Rivedal et al. 2022, 2024; Schoener & Wang 2023). In 2022, 35 hemp (Cannabis sativa) plants were observed at the Washington State University (WSU) Research Station in Othello, WA, with typical symptoms of BCTV (a finding published by Jarugula et al. 2023) and we further tested these samples for C. tenellus-associated bacteria. In 2024, 23 and 15 hemp plants observed in Prosser, WA, from the WSU Irrigated Agriculture Research Center and WSU Roza Farm, respectively, with symptoms of CPt infection, including stem fasciation and purpling. Leaf tissue from each plant was ground in liquid nitrogen, DNA extracted using the DNeasy Plant Mini Kit (Qiagen, Inc.), and a multiplex real-time PCR protocol used to detect the C. tenellus-associated pathogens (Swisher Grimm et al. 2023). CPt was identified in 8.6% and 65.8% of plants in 2022 and 2024, respectively, while S. citri was not detected in 2022 but was found in 15.8% of plants in 2024. Co-infections were common. Nested PCR (primers P1/P7 and R16F2n/R16R2, Crosslin et al. 2006) and conventional PCR (primers Trif-SecY-163F, 5ʹ-AGCAGCTAAAAAAGTTAGAAAAAACCTC-3ʹ/Trif-SecY-1040R, 5ʹ-AAATCTAGCGAAAATGATTTTTTGTTTTCA-3ʹ) targeted the CPt 16S rRNA and secY genes, respectively. S. citri infection was confirmed by PCR targeting the spiralin gene (primers SpiralinF/R, Yokomi et al. 2008). All targets were amplified using PrimeSTAR HS DNA polymerase (Takara Bio Inc.). Thermal cycle conditions for CPt 16S rRNA and S. citri spiralin genes consisted of 30 or 40 cycles, respectively, at 98°C for 10 s, 55°C for 15 s, and 72°C for 10 s, followed by a final elongation at 72°C for 5 min. Conditions for CPt secY consisted of 35 cycles at 98°C for 15 s, 55°C for 30 s, and 72°C for 10 s, followed by a final elongation at 72°C for 5 min. Amplicons of size 1,250 bp, 877 bp, and 675 bp for the 16S rRNA, secY, and spiralin genes, respectively, were visualized on an agarose gel stained with GelRed (Sigma-Aldrich) or Ethidium Bromide. For CPt, sequencing of 16S rRNA from seven infected samples (2 from 2022, 5 from 2024) revealed identical sequences (GenBank Accession PV983691) with 100% identity to CPt in U.S. hemp (OQ597521), and sequencing of secY in one sample from 2022 and one from 2024 revealed identical sequences (PX725980), with 100% identity to CPt in U.S. periwinkle (GU004317). For S. citri, two sequenced samples had identical spiralin sequences (PV955037), matching 100% and 99.85% with S. citri found in Oregon cabbage (PV099668) and hemp (OQ969984), respectively. This is the first confirmed report of CPt and S. citri in C. sativa in Washington state. These findings highlight the need to evaluate effects of mollicutes on hemp and underscore the need to develop integrated pest management strategies to reduce vector transmission. In addition, these findings suggest that hemp could serve as a reservoir of the C. tenellus-transmitted pathogens, leading to higher pathogen prevalence across the region, and negatively impacting economically important vegetable and seed crops grown in Washington state that are susceptible to these pathogens.
Development of a Loop-Mediated Isothermal Amplification (LAMP) Method to Detect the Potato Zebra Chip Pathogen ‘Candidatus Liberibacter solanacearum’ (Lso) and Differentiate Haplotypes A and B
‘Candidatus Liberibacter solanacearum’ (Lso) is the causal agent of zebra chip of potato (Solanum tuberosum), which can significantly reduce potato yield. In this study, a loop-mediated isothermal amplification (LAMP) method for the detection of Lso haplotypes A and B was developed and evaluated. Two sets of LAMP primers named LAMP-A and LAMP-B were designed and tested for specificity and sensitivity. Both LAMP-A and LAMP-B were specific to Lso in in silico analysis using the Primer-Blast tool. The LAMP-A and LAMP-B could only produce positive signals from DNA mixtures of Lso-infected tomato but not from the genomic DNA of 37 nontarget plant pathogens. The sensitivity of LAMP-A and LAMP-B on Lso haplotypes A and B were tested on gBlocks and genomic DNA from Lso-infected tomato. On the genomic DNA for LAMP-A, the lowest amount of template DNA for a positive LAMP reaction was 2 to 20 ng on four haplotype A strains and 20 to 80 ng on four haplotype B strains; for LAMP-B, the lowest amount of template DNA for a positive LAMP reaction was 0.02 to 2 ng on four haplotype B strains and 20 ng to no amplification on four haplotype A strains. On gBlocks for LAMP-A, the lowest number of copies for a positive LAMP reaction was 60 on haplotype A and 600 on haplotype B; for LAMP-B, the lowest number of copies for a positive LAMP reaction was 60 on haplotype B and 600 on haplotype A. Therefore, considering the convenience of the LAMP technique, as well as the high specificity and sensitivity, the LAMP-A and LAMP-B primers can be used together to test the probable Lso-infected plant or psyllid samples to rapidly, accurately, and directly differentiate haplotypes A and B. We highly recommend this LAMP system to plant pathology practitioners and diagnostic labs for routine detection of Lso and confirmation of zebra chip disease on potato or tomato.
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