# Validation and Improvement of a Rapid, CRISPR-Cas-Free RPA-PCRD Strip Assay for On-Site Genomic Surveillance and Quarantine of Wheat Blast

## TL;DR

This paper presents a fast, portable, and easy-to-use diagnostic test for detecting wheat blast, a dangerous plant disease, in the field without needing lab equipment.

## Contribution

The study validates and improves a CRISPR-free RPA-PCRD strip assay for rapid and specific detection of wheat blast in resource-limited settings.

## Key findings

- The RPA-PCRD strip assay detected Magnaporthe oryzae pathotype Triticum (MoT) at 10 pg/µL with no cross-reactivity to other pathogens.
- The assay detected MoT in wheat leaves as early as 4 days post-infection and in infected spikes, seeds, and alternate hosts.
- The method enabled detection of MoT within 30 minutes at ambient temperature using a simplified DNA extraction method.

## Abstract

As an emerging threat to global food security, wheat blast necessitates the development of a rapid and field-deployable detection system to facilitate early diagnosis, enable effective management, and prevent its further spread to new regions. In this study, we aimed to validate and improve a Recombinase Polymerase Amplification coupled with PCRD lateral flow detection (RPA-PCRD strip assay) kit for the rapid and specific identification of Magnaporthe oryzae pathotype Triticum (MoT) in field samples. The assay demonstrated exceptional sensitivity, detecting as low as 10 pg/µL of target DNA, and exhibited no cross-reactivity with M. oryzae Oryzae (MoO) isolates and other major fungal phytopathogens under the genera of Fusarium, Bipolaris, Colletotrichum, and Botrydiplodia. The method successfully detected MoT in wheat leaves as early as 4 days post-infection (DPI), and in infected spikes, seeds, and alternate hosts. Furthermore, by combining a simplified polyethylene glycol-NaOH method for extracting DNA from plant samples, the entire RPA-PCRD strip assay enabled the detection of MoT within 30 min with no specialized equipment and high technical skills at ambient temperature (37–39 °C). When applied to field samples, it successfully detected MoT in naturally infected diseased wheat plants from seven different fields in a wheat blast hotspot district, Meherpur, Bangladesh. Training 52 diverse stakeholders validated the kit’s field readiness, with 88% of trainees endorsing its user-friendly design. This method offers a practical, low-cost, and portable point-of-care diagnostic tool suitable for on-site genomic surveillance, integrated management, seed health testing, and quarantine screening of wheat blast in resource-limited settings. Furthermore, the RPA-PCRD platform serves as an early warning modular diagnostic template that can be readily adapted to detect a wide array of phytopathogens by integrating target-specific genomic primers.