Glyphosate resistance of molecularly identified Conyza albida and Conyza bonariensis populations

In the initial screening, 18 out of 32 Conyza albida and 7 out of 28 Conyza bonariensis populations, sampled from main perennial crop regions of central and southern Greece, were found to be resistant to glyphosate. The level of resistance determined in dose–response experiments with representative populations of the two species was found to range from 7.7 to 37.3 for C. albida and from 3.4 to 7.8 for C. bonariensis. The comparison of the resistant and susceptible C. albida and C. bonariensis EPSPS gene sequences indicated that possess single nucleotide changes compared to Conyza canadensis EPSPS gene, but none of these changes is located at the position 106 that has been reported to confer resistance to glyphosate. Finally, the cpDNA sequence comparison analysis used for the most resistant population of each species and the respective susceptible counterparts was found to be a reliable tool for discrimination of conventionally classified C. albida and C. bonariensis plants that are morphologically similar. This is the first report for molecular identification of Conyza species.