Physiological studies of mecoprop‐resistance in chickweed (Stellaria media L.)

Summary Glasshouse experiments have confirmed that resistance to mecoprop is present in a biotype of Stellaria media. Resistant plants were less vigorous than the susceptible population and ED 50 values were calculated as 3·92 and 0·18 kg a.i. ha −1 respectively. The physiological basis of mecoprop resistance was investigated by studying the responses of each biotype in two experimental systems, namely explant stem elongation and ethylene evolution. These studies have discounted differential ethylene evolution as the basis of resistance but have indicated altered elongation growth in resistant plants. This observation suggests the possibility of reduced mecoprop binding in resistant plants, although the role of mecoprop metabolism remains to be elucidated.