Water chickweed is a widespread and competitive winter annual or biennial weed of wheat in China. One
Water chickweed population (HN02) resistant to several acetolactate synthase (ALS) inhibitors was found
in Henan province of China. Whole-plant bioassays showed that HN02 was high resistance to tribenuron
(292.05-flod). In vitro ALS assays revealed that resistance was due to reduced sensitivity of the ALS
enzyme to tribenuron. This altered ALS sensitivity in the resistant population was due to a mutation in
the ALS gene resulting in a Pro197 to Ser substitution. Cross-resistance experiments indicated that HN02
exhibited various resistance patterns to pyrithiobac-sodium, f