Nol N, Tsikou D, Eid M, Livieratos IC & Giannopolitis CN (2012). Shikimate leaf disc assay for early detection of glyphosate resistance in Conyza canadensis and relative transcript levels of EPSPS and ABC transporter genes. Weed Research52, 233–241.
Twenty-two biotypes of Conyza canadensis (Canadian fleabane, horseweed) from a conventional orchard in Crete displayed varying degrees of reduced glyphosate susceptibility in standard whole plant assays. A refined shikimate leaf disc assay was developed to precisely determine the resistance levels, permitting early detection of resistance evolution and integrated management of the weed. The 5-enolpyruvoylshikimate-3-phosphate synthase (EPSPS) homologue genes (1 and 2) were sequenced for three different biotypes (one of reduced susceptibility from Crete, one resistant from mainland Greece and one resistant from the USA), and no amino acid substitution of Pro106 was found. Real-time qRT-PCR was used to study the expression profiles for EPSPS and the M10 and M11 ABC transporter genes, following glyphosate application. The expression levels of the EPSPS genes were not significantly altered following glyphosate application in any biotype, but both M10 and M11 were found to be highly upregulated in glyphosate-treated reduced susceptibility or resistant biotypes and not in a susceptible biotype. These results are in accordance with data recently reported by other researchers, supporting a role of the M10 and M11 ABC transporter genes in glyphosate resistance in Conyza canadensis, because of reduced translocation.