Distribution of target-site resistance mechanisms to nicosulfuron and glyphosate in Amaranthus palmeri accessions from two different regions of Turkiye

Palmer amaranth, a resilient weed, has developed resistance to herbicides in Turkiye, causing concern among farmers. This investigation aimed to identify the prevalence of resistance mechanisms to two specific herbicides, nicosulfuron and glyphosate, in A. palmeri samples from two distinct regions: the Cukurova Region and the Gediz Basin.

The researchers examined 96 plant samples for mutations in the ALS gene and variations in the EPSPS gene copy number, as well as measured their response to nicosulfuron and glyphosate at twice their field application rates. The ALS mutations Pro197Ser, Trp574Leu, and Ser653Asn were significantly more common in Cukurova Region plants compared to Gediz Basin plants.

The Gediz Basin plants exhibited a higher relative EPSPS gene copy number. Field trials confirmed that Cukurova Region plants had a greater response to nicosulfuron, while Gediz Basin plants were more resistant to glyphosate. Statistical analysis showed that the Pro197Ser and Trp574Leu mutations were the primary factors influencing nicosulfuron resistance, while EPSPS gene copy number variation was the main determinant of glyphosate resistance.

These results highlight regional disparities in resistance profiles of A. palmeri in Turkiye, likely influenced by local agricultural practices, resistance introduction history, and genetic factors. However, the precise interplay between selection pressure, population dynamics, and gene flow requires further investigation.