THE MECHANISM OF DIFFERENTIAL RESPONSE OF WHEAT CULTIVARS TO CHLORSULFURON

Wheat (Triticum aestivum L.) cultivars showed differential tolerance to chlorsulfuron. Cultivar Kotare showed no injury symptoms following foliar applications of chlorsulfuron at 15 or 60 g a.i. ha-1, while cultivars Rongotea and Lancer showed early damage in pot and field experiments at both rates of chlorsulfuron. Cultivars Abele and Jasper were intermediate in their response. The number of spikelets per ear was the only yield component affected by chlorsulfuron and was reduced in Lancer and Rongotea. Retention, uptake and translocation of chlorsulfuron were not different between Kotare and Rongotea. Within 48 h of application, Kotare metabolized 92.2% of [C-14]chlorsulfuron, while Lancer and Rongotea metabolized only 43.5% and 63% of the herbicide, respectively. The concentration of chlorsulfuron in young tissues of Kotare, Lancer and Rongotea, 48 h after application was calculated as 1.2, 31.9 and 15.6 ng g-1 dry weight, respectively. It is concluded that differential rates of metabolism are the main reason for differences in sensitivity to chlorsulfuron between the wheat cultivars tested.