Development and Application of a Loop-Mediated Isothermal Amplification (LAMP) Assay for the Detection of Pseudomonas syringae Pathovars pisi and syringae

Pseudomonas syringae causes bacterial blight (BB) disease worldwide on economically important fruit and vegetable crops including field pea (Pisum sativum L.). The two pathovars responsible for BB in field pea are Pseudomonas syringae pathovar pisi (Psp) and syringae (Pss). In the field, both pathovars cause indistinguishable symptoms on field pea and require laboratory diagnosis to determine the causal pathovar. To aid in-field and laboratory diagnosis, accurate, and robust loop-mediated isothermal amplification (LAMP) assays for Psp and Pss were developed. The assays were able to detect Psp or Pss on live or heat-killed bacterial cells, plant exudates, seeds, and DNA extracts with no inhibitory effects. The two specific LAMP assays developed detected Psp and Pss accurately in less than 20 min and no cross-reaction was observed with 18 strains of closely related species of Pseudomonas syringae. Compared to the conventional PCR assays, the two LAMP assays were equally specific but have advantages of producing quicker and visual live results, enabling early detection and differentiation of Psp and Pss. Our results suggested a potential use of LAMP assays for laboratory testing and can be applied for in-field surveys.