Event-specific qualitative and quantitative detection of three genetically modified papaya events using a single standard reference molecule

Abstract A novel standard reference plasmid (pGEM-PAPAYA3) was constructed as a positive control and reference standard for event-specific qualitative and quantitative detection of genetically modified (GM) papaya (55-1, 16-0-1, and Huanong No.1). The plasmid pGEM-PAPAYA3 contained the specific fragments of papaya endogenous reference gene chymopapain and the 3 GM papaya events. The qualitative PCR assay using pGEM-PAPAYA3 was established with a limit of detection correlating to approximately 5–50 copies of papaya haploid genomes. In the quantitative PCR assay, the square regression coefficients ( R 2 ) ranged from 0.993 to 0.997. The standard deviation and relative standard deviation values for repeatability ranged from 0.04 to 0.25 and 0.05%–0.86%, respectively. The method was used to test 11 papaya products purchased from Thailand, China, the Philippines and the USA, and the results revealed 2 varieties of GM papaya in 5 of the 11 samples tested. These results indicate the developed detection methods with the standard reference plasmid are applicable for identifying 3 GM papaya events.