Papaya leaf distortion mosaic virus (PLDMV) can infect transgenic papaya resistant to a related pathogen, Papaya ringspot virus (PRSV), posing a substantial threat to papaya production in China.Current detection methods, however, are unable to be used for rapid detection in the field.Here, a reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for the detection of PLDMV, using a set of four RT-LAMP primers designed based on the conserved sequence of PLDMV CP.The RT-LAMP method detected specifically PLDMV and was highly sensitive, with a detection limit of 1.32×10-6μg of total RNA per reaction.Indeed, the reaction was 10 times more sensitive than one-step RT-PCR, while also requiring significantly less time and equipment.The effectiveness of RT-LAMP and one-step RT-PCR in detecting the virus were compared using 90 field samples of non-transgenic papaya and 90 field samples of commercialized PRSV-resistant transgenic papaya from Hainan Island.None of the non-transgenic papaya tested positive for PLDMV using either method.In contrast, 19 of the commercialized PRSV-resistant transgenic papaya samples tested positive by RT-LAMP assay, and 6 of those tested negative by RT-PCR.Therefore, the PLDMV-specific RT-LAMP is a simple, rapid, sensitive, and cost-effective tool in the field diagnosis and control of PLDMV.