Evaluation of a loop-mediated isothermal amplification assay based on hrpZ gene for rapid detection and identification of Pseudomonas syringae pv. lachrymans in cucumber leaves.

AIMS: Cucumber angular leaf spot caused by Pseudomonas syringae pv. lachrymans (Psl) is an important and destructive disease worldwide, and no effective technique has been developed for the control of the pathogen. Detection of infection or latent in cucumber plants is critical to evaluate disease progress and strengthening management to avoid a serious epidemic in the fields. In this paper, we developed a rapid and sensitive method for detection of Psl using an isothermal method known as loop-mediated amplification (LAMP).

METHODS AND RESULTS: A set of six primers was designed to amplify the gene coding for the hrpZ, and conditions for detection were optimized to complete in 60 min at 67°C, and the amplification were confirmed through gel electrophoresis or visually inspected using calcein stain. The specificity of LAMP primers set was widely validated on Psl and nontarget strains. In sensitivity testing, LAMP allowed detection as low as 10(4)  CFU per ml bacterial cells without DNA extraction. The novel method was also applied for detecting Psl in infected cucumber leaves, and even the early onset of disease can be detected by the assay.

CONCLUSIONS: This study confirmed that the novel developed LAMP assay is an easy, rapid and sensitive method for the detection of Psl in infected leaves.

SIGNIFICANCE AND IMPACT OF THE STUDY: The method is suitable for direct detection of Psl without strain enrichment and complex DNA extraction from samples in the field, and hence it has the capability to be used for on-site disease diagnosis and field surveys.