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ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Publications at this Location » Publication #429703
Research Project: Detection, Biology, and Genomics of New and Emerging Viral and Bacterial Diseases of Ornamental Plants

Location: Floral and Nursery Plants Research

Title: Evaluation of enrichment to improve qPCR detection of Ralstonia solanaceraum in latently infected geranium plants

Author
item INABA, JUNICHI - Oak Ridge Institute For Science And Education (ORISE)
item SAAR, LILY - Oak Ridge Institute For Science And Education (ORISE)
item SANTILLANA, GEM - Animal And Plant Health Inspection Service (APHIS)
item Huang, Qi

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2026
Publication Date: 5/12/2026
Citation: Inaba, J., Saar, L., Santillana, G., Huang, Q. 2026. Evaluation of enrichment to improve qPCR detection of Ralstonia solanaceraum in latently infected geranium plants. PhytoFrontiers. 6. Article 3. https://doi.org/10.1094/PHYTOFR-09-25-0111-R.
DOI: https://doi.org/10.1094/PHYTOFR-09-25-0111-R

Interpretive Summary: A bacterium causes a serious disease in potato, especially in cool weather (<25C), and is not allowed to enter the United States. However, it can accidently be brought into the U.S. through geranium plants that looks healthy but contain the bacterium. To help find the bacterium more easily, we need to increase the number of bacterial cells in these plants so it can be picked up by lab tests. To do this, we used a special process called enrichment and tested three microbe-growing mixtures called media to see which one worked better. We found that all three media helped increase bacterial levels and improved detection in healthy-looking geraniums. However, they did not work consistently when the bacterial levels were very low. Our research will help scientists detect this dangerous bacterium more accurately and protect U. S. plant nurseries from it being unintentionally brought in.

Technical Abstract: Ralstonia solanacearum race 3 biovar 2 (r3b2), a U.S. select agent pathogen, causes brown rot of potato under cool conditions and has been unintentionally introduced into the U.S. multiple times through latently infected geranium cuttings. To improve molecular detection in asymptomatic tissue, bacterial enrichment is often necessary. This study evaluated a 24-hour enrichment protocol using three media, mCPG, mSMSA, and mCPG with antibiotics (mCPG+Ab), for their ability to enhance qPCR detection of R. solanacearum r3b2 strain UW551 and non-r3b2 strain RUN302 in 51 UW551- and 28 RUN302-inoculated geranium plants. No significant difference was observed among the media, indicating antibiotics did not affect qPCR detection when using specific primers and probes. In symptomatic plants (n=14), initial qPCR Cq values were consistently < 25 (range of 17.59-24.53). In asymptomatic plants (n=65), Cq values ranged from 20.43 to undetectable. Enrichment significantly improved qPCR detection in samples with initial Cq < 34. For samples with Cq = 34, results were variable: some showed substantial improvement (Cq reductions up to 13.65 for UW551 and 16.43 for RUN302), while others showed little or no improvement. Overall, 24-hour enrichment in mCPG, mSMSA, or mCPG significantly enhanced qPCR detection of both r3b2 and non-r3b2 strains in symptomatic and asymptomatic geraniums, although its effectiveness was inconsistent when initial bacterial populations are very low (Cq = 34). These findings support the use of enrichment for improving detection sensitivity but highlight limitations in reliably recovering very low pathogen levels.