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Authors Cowell

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Cowell, Sarah


Publications
2

CitationNamesAbstract
Effect of nucleic acid extraction methodology and PCR chemistry on the detection of ‘ Candidatus Phytoplasma pruni’ in sweet cherry Cowell, Harper (2026). Plant Disease Ca. Phytoplasma pruni
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Reservoir or Island? Chokecherry ( Prunus virginiana L.) as a host of ‘ Candidatus Phytoplasma pruni’-related strains Hoskins et al. (2026). Plant Disease Ca. Phytoplasma pruni
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Effect of nucleic acid extraction methodology and PCR chemistry on the detection of ‘ Candidatus Phytoplasma pruni’ in sweet cherry
Early and accurate detection of ‘Candidatus Phytoplasma pruni’ is essential for the control of X-disease in Prunus species, but this is made difficult by pathogen biology and the ability to consistently recover nucleic acids, both of which increase the likelihood of false negatives. Here we examined the latter, using high- and low-titer infected sweet cherry (P. avium) samples to compare three tissue disruption methods, four nucleic acid extraction chemistries, and four PCR chemistries. Results showed that method selection had minimal impact on high-titer samples but significantly affected low-titer detection. Bead-beating disruption consistently outperformed rotary and manual grinding, yielding lower Cq values and more reliable amplification. Among extraction methods, CTAB-based protocols provided the highest nucleic acid recovery and detection sensitivity, particularly when paired with bead beating. Column- and magnetic bead–based kits performed less consistently, especially with low-titer samples, where false negatives were frequent. PCR chemistry also influenced results, although RT-qPCR did not significantly improve sensitivity over qPCR. Importantly, commonly used host internal controls failed to reliably indicate pathogen detection success, as high-abundance targets masked poor extraction efficiency. Cumulatively these data suggest the need for optimizing diagnostic protocols to ensure capture of low-concentration pathogens to avoid false negatives.
Reservoir or Island? Chokecherry ( Prunus virginiana L.) as a host of ‘ Candidatus Phytoplasma pruni’-related strains
Chokecherry (Prunus virginiana L.) is a native shrub that is widely found across North America and is a host of ‘Candidatus Phytoplasma pruni’ associated with X-disease of stone fruits. This pathogen is of major concern to U.S. cherry and peach growers, with the most recent and ongoing outbreak in the Pacific Northwest causing major economic harm. To investigate the role of chokecherry as a potential reservoir and source of orchard-associated strains, we surveyed wild chokecherry trees across 12 U.S. states, and compared the strains present to those in commercially cultivated Prunus species. Approximately 47% of chokecherry sampled tested positive for a ‘Ca. P. pruni’-related strain and phylogenetic analysis revealed high strain diversity, including six distinct clades and four newly identified lineages. In contrast, ‘Ca. P. pruni’ strains isolated from cultivated cherry and peach trees exhibited lower diversity and were infected by known disease outbreak-associated strains such as NWX. These data suggest limited transmission between wild and cultivated hosts in the western U.S., with patterns indicating spillover from orchards into nearby chokecherry populations rather than the reverse. However, in states east of the Rocky Mountains, chokecherry likely functions as a reservoir for orchard infections.
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