ACETOLACTATE SYNTHASE ACTIVITY AND CHLORSULFURON SENSITIVITY OF WHEATCULTIVARS

Differences were observed in the sensitivity of three wheat (Triticum aestivum L.) cultivars to chlorsulfuron. Shoot dry weight was reduced by foliar applications of chlorsulfuron to a greater extent in cv. Ron gotea than in cvs Lancer and Kotare. There was no difference between t hese cultivars in the specific activity of acetolactate synthase (ALS) enzyme extracted from leaves or roots. Moreover, chlorsulfuron inhibi ted ALS from the wheat cultivars to the same extent in vitro. ALS meas urement in vivo showed that after 15 h of incubating excised leaf tiss ues with chlorsulfuron, there was a greater reduction in ALS enzyme ac tivity in Rongotea than in the other cultivars. Furthermore, 1 day aft er a foliar application of chlorsulfuron, in vitro ALS activity in lea ves was reduced more in Rongotea than in Lancer or Kotare. Recovery of the enzyme activity following chlorsulfuron application was quicker i n Kotare than in Lancer or Rongotea. It is concluded that differences in sensitivity of these wheat cultivars to chlorsulfuron are not due t o differential ALS sensitivity or level, but may be due to differentia l rates of herbicide metabolism.