<p>The development of quick and affordable diagnostic methods is crucial for managing plant viral diseases. This study establishes a novel Recombinase Polymerase Amplification (RPA) assay for detecting mungbean yellow mosaic India virus (MYMIV) for the first time in wild <i>Vigna</i> germplasm. We designed and validated three primer pairs targeting the MYMIV coat protein gene. Using crude sap extracted with 0.5 M phosphate buffer—the most effective of ten lysis buffers tested—optimal amplification was achieved at 45 °C for 30 minutes. The RPA assay demonstrated exceptional sensitivity, detecting MYMIV in crude sap at a dilution of 10⁻⁹, whereas conventional PCR failed to amplify from crude extracts. With purified DNA, RPA and PCR showed detection limits of 10⁻⁷ and 10⁻⁶, respectively. The assay was highly specific, with no cross-reactivity against other legume-infecting viruses like dolichos yellow mosaic virus, horsegram yellow mosaic virus, and bean common mosaic virus. The entire RPA procedure, from sample to result, required only 60–90 minutes, offering a significant time saving over PCR (~3–3.5 hours). This optimized, crude sap-based RPA protocol provides a sensitive, specific, and practical tool for MYMIV detection, proving particularly valuable for resource-limited settings, field applications, and the identification of latent infections in wild <i>Vigna</i> germplasm.</p>