First evidence for a target site mutation in the EPSPS2 gene in glyphosate-resistant Sumatran fleabane from citrus orchards

The glyphosate herbicide has been extensively used for long time periods in woody crops to control a broad range of weeds. The rapid determination of resistant weeds in different woody crops could maintain the efficacy of herbicides and could improve weed management using rotating strategies. Unfortunately Sumatran fleabane has developed a resistance to glyphosate. The mechanism of resistance of Sumatran fleabane is unknown so far. Therefore, here, we studied the resistance of a Sumatran fleabane biotype collected from a citrus orchard, under greenhouse and laboratory conditions. Our results show a resistance factor of 7.4. The resistant biotype absorbed and translocated lower amounts of ¹⁴C-glyphosate compared to the susceptible biotype. Moreover, at the molecular level, the target site sequence of the EPSPS2 gene showed a Pro-182-Thr substitution in the resistant biotype. As a consequence, this biotype uses mechanisms of reduced absorption-translocation and target site mutation to resist against glyphosate. This is the first study to report the reduced absorption and a mutation in the EPSPS2 gene in the resistance mechanism in the Conyza genus.