Differences in metabolism of three Conyza species to herbicides glyphosate and triclopyr revealed by LC-MS/MS

Abstract

Conyza spp. are among the most common weeds found in perennial crops, and resistance to several herbicides has already occurred worldwide. In the present study, pot and laboratory experiments were conducted to evaluate differences in glyphosate and triclopyr susceptibility between different biotypes of Conyza spp. Plant material was obtained from seeds collected in perennial crops in Greece. Seeds of four Conyza spp. biotypes were sown in separate pots and treated with glyphosate at the rosette stage, while seeds of six different Conyza spp. biotypes were sown and treated with triclopyr. Twenty-four hours after the herbicide treatment, the aboveground part of the weeds was manually collected and plant samples were prepared to determine the analytes with LC-MS/MS. In two C. bonariensis biotypes, the glyphosate concentration was 50% to 52% lower than for other biotypes; therefore, they could be considered as potentially resistant to glyphosate because the resistant biotype had a stronger and faster metabolism than the sensitive biotype, transforming glyphosate into non-toxic metabolites. The higher glyphosate concentration was detected in C. canadensis biotypes, which proved to be potentially susceptible to glyphosate. Three C. bonariensis biotypes and one C. albida biotype were less susceptible to triclopyr because analytes were detected in 63% to 82% higher concentrations than the two C. canadensis biotypesthat were susceptible to triclopyr. These results reveal significant differences between the three species, confirm the problem of herbicide resistance, and suggest that glyphosate and triclopyr efficacy in Conyza spp. is merely due to herbicide metabolism to other compounds.