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ARS Home » Southeast Area » Poplarville, Mississippi » Southern Horticultural Research Unit » Research » Publications at this Location » Publication #410477
Research Project: Management of Diseases, Pests, and Pollinators of Horticultural Crops

Location: Southern Horticultural Research Unit

Title: Development of a quantitative qPCR method to detect the bacterial gall pathogen Pseudomonas amygdali pv. loropetali from Loropetalum plant materials

Author
item JIA, JIAYUAN - Mississippi State University
item PHILLIPS, KATE - Mississippi State University
item WILLIS, EMMA - Mississippi State University
item PHILLIPS, WES - Mississippi State University
item Copes, Warren
item LU, SHI-EN - Mississippi State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2025
Publication Date: 5/22/2025
Citation: Jia, J., Phillips, K., Willis, E., Phillips, W., Copes, W.E., Lu, S. 2025. Development of a quantitative qPCR approach to detect the bacterial gall pathogen Pseudomonas amygdali pv. loropetali from Loropetalum plant materials. Plant Disease. https://doi.org/10.1094/PDIS-11-23-2533-SR.
DOI: https://doi.org/10.1094/PDIS-11-23-2533-SR

Interpretive Summary: Bacterial gall disease caused by Pseudomonas amygdali pv. loropetali is a relatively new disease that has become a prevalent problem on Loropetalum shrubs in commercial plant nurseries in the southern and southeastern US. Little is known about the pathogen, so research is needed to develop reliable control approaches. First, we need a tool that gives us the ability to readily detect the bacterium and monitor its seasonal activities in nurseries. Based on a genome wide analysis, a pair of genetic primers with a probe were designed from the AraC regulator locus. These genetic markers provide a reliable method to specifically detect the presence of P. amygdali pv. loropetali on and in Loropetalum plant tissues and on surrounding production surfaces, even if other plant pathogenic Pseudomonas species are present. Identification of these primers and probe will help research scientists investigate this pathogen in nurseries and help diagnostic laboratories verify the presence of this pathogen.

Technical Abstract: Bacterial gall disease caused by Pseudomonas amygdali pv. loropetali is a significant problem on Loropetalum chinense shrubs in commercial plant nurseries. Research was conducted to develop a reliable method to detect the presence of the pathogen on vegetative propagation stem cuttings and other tissue types. Genomewide analysis identified a genetic locus encoding an AraC regulator that was specific to P. amygdali pv. loropetali, thus a pair of primers with a probe were designed from the genetic region. Positive results of PCR amplification were obtained with DNA from all P. amygdali pv. loropetali strains but not from any other strains of Pseudomonas species. Melting curve analysis demonstrated that all PCR products shared the same melting temperature of 79°C. TaqMan-based qPCR analysis of the AAC genomic DNA exhibited a strong linear response of bacterial cell numbers with the Ct value (R2=0.9986) and amplification efficiency (E=1.96). The detection limit of the reaction was ten cells of the target pathogenic bacteria from pure culture. The qPCR approach was able to provide reliable qPCR positive results when a plant material sample contained more than 2,500 bacterial cells. The qPCR approach is useful for detection of P. amygdali pv. loropetali strains associated with plant tissue.