Molecular basis of Cyperus difformis cross-resistance to ALS-inhibiting herbicides

Applications of 64 times higher rates of azimsulfuron and halosulfuron-methyl failed to reduce by 50% growth of 10 putative resistant (R) Cyperus difformis (smallflower umbrella-sedge) populations collected from rice fields located in Northern Greece. However, the growth rate of the susceptible (S) population was reduced by 50% by 1/4 of the recommended rate of both herbicides. The als gene sequencing identified point mutations at Pro-197 position, leading to amino acid substitution by Ala or Ser of the ALS enzyme. The in vitro activity of the ALS enzyme indicated that the 150 values (herbicide concentration required for 50% reduction of the ALS activity) ranged from 10.7 to 55.5 mu M azimsulfuron and from 6.7 to 50.6 mu M halosulfuron-methyl, whereas the respective values for the S population were 0.09 and 0.11 mu M. These results strongly support that cross-resistance of 10 C. difformis populations was due to point mutations of the als gene, which resulted in a less-sensitive ALS enzyme. This study reports the presence of a 1240 bp intron in the C difformis als gene with the Pro-197 point mutations near the splice junction. (c) 2015 Elsevier Inc. All rights reserved.