Target-site resistance to bensulfuron-methyl in Sagittaria trifolia L. populations

Sagittaria trifolia L. is one of the most serious weeds in paddy fields in northeast of China and cannot be controlled effectively by bensulfuron-methyl in recent years. In this study, two suspected resistant S. trifolia populations (R1 and R2) were collected in Liaoning province of China. Whole-plant dose-response studies showed that R1 and R2 were highly resistant to bensulfuron-methyl, with the GR50 R/S ratios of 76.99 and 49.94 respectively. In vitro acetolactate synthase (ALS) assays revealed that resistance was due to reduced sensitivity of the ALS to bensulfuron-methyl inhibition, with I50 R/S ratios of 81.86 and 67.48 for R1 and R2, respectively. Total ALS activity was similar for the S and R2 populations, whereas the R1 population displayed significantly higher ALS activity than did the S population. The mutations Pro-197-Leu and Pro-197-Ser were identified in the ALS gene of the R1 and R2 populations, respectively. This is the first report examining bensulfuron-resistant S. trifolia in Liaoning province, China. The Pro197 mutation is likely responsible for resistance to bensulfuron-methyl in S. trifolia populations.