# Rapid Visual Detection of Peronophythora litchii on Lychees Using Recombinase Polymerase Amplification Combined with Lateral Flow Assay Based on the Unique Target Gene Pl_101565

## TL;DR

A new rapid test for detecting Peronophythora litchii in lychees was developed using a unique gene and a portable method, enabling quick and accurate diagnosis in the field.

## Contribution

A novel RPA-LF assay based on the unique gene Pl_101565 for rapid and specific detection of P. litchii is introduced.

## Key findings

- The RPA-LF assay detects P. litchii with high specificity and no cross-reactivity to other pathogens.
- The assay can detect as low as 1 pg of P. litchii genomic DNA within 15 to 25 minutes.
- The method successfully identified P. litchii in infected lychee samples within 30 minutes.

## Abstract

Downy blight, caused by Peronophythora litchii, is a destructive disease that impacts lychee fruit throughout the pre-harvest, post-harvest, and transportation phases. Therefore, the prompt and precise identification of P. litchii is crucial for the effective management of the disease. A novel gene encoding a Rh-type ammonium transporter, Pl_101565, was identified in P. litchii through bioinformatic analysis in this study. Based on this gene, a coupled recombinase polymerase amplification–lateral flow (RPA-LF) assay for the rapid visual detection of P. litchii was developed. The assay has been shown to detect P. litchii accurately, without cross-reactivity to related pathogenic oomycetes or fungi. Moreover, it can be performed effectively within 15 to 25 min at temperatures ranging from 28 to 46 °C. Under optimized conditions, the RPA-LF assay could detect as low as 1 pg of P. litchii genomic DNA in a 25 μL reaction system. Furthermore, the RPA-LF assay successfully detected P. litchii in infected lychee samples within a 30 min timeframe. These attributes establish the RPA-LF assay as a rapid, sensitive, and specific method for diagnosing P. litchii early; it is particularly suitable for applications in resource-limited settings.