Rapid and specific detection of Yam mosaic virus by reverse - transcription recombinase 1 polymerase amplification 2 3 4

28 Yam mosaic virus (YMV; genus Potyvirus) is considered to cause the most economically important 29 viral disease of yams (Dioscorea spp.) in West Africa which is the dominant region for yam 30 production globally. 31 Yams are a vegetatively propagated crop and the use of virus-free planting material forms an essential 32 component of disease control. Current serological and PCR-based diagnostic methods for YMV are 33 time consuming involving a succession of target detection steps. 34 In this study, a novel assay for specific YMV detection is described that is based on isothermal 35 reverse transcription-recombinase polymerase amplification (RT-exoRPA). This test has been shown 36 to be reproducible and able to detect as little as 14 pg/μl of purified RNA obtained from an YMV37 infected plant, a sensitivity equivalent to that obtained with the reverse transcription-polymerase chain 38 reaction (RT-PCR) in current general use. The RT-exoRPA assay has, however, several advantages 39 over the RT-PCR; positive samples can be detected in less than 30 min, and amplification only 40 requires a single incubation temperature (optimum 37°C). These features make the RT-exoRPA assay 41 a promising candidate for adapting into a field test format to be used by yam breeding programmes or 42 certification laboratories. 43 44 45 46