THE MECHANISM OF DIFFERENTIAL RESPONSE OF WHEAT CULTIVARS TO CHLORSULFURON

Wheat (Triticum aestivum L.) cultivars showed differential tolerance t o chlorsulfuron. Cultivar Kotare showed no injury symptoms following f oliar applications of chlorsulfuron at 15 or 60 g a.i. ha-1, while cul tivars Rongotea and Lancer showed early damage in pot and field experi ments at both rates of chlorsulfuron. Cultivars Abele and Jasper were intermediate in their response. The number of spikelets per ear was th e only yield component affected by chlorsulfuron and was reduced in La ncer and Rongotea. Retention, uptake and translocation of chlorsulfuro n were not different between Kotare and Rongotea. Within 48 h of appli cation, Kotare metabolized 92.2% of [C-14]chlorsulfuron, while Lancer and Rongotea metabolized only 43.5% and 63% of the herbicide, respecti vely. The concentration of chlorsulfuron in young tissues of Kotare, L ancer 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 differ ential rates of metabolism are the main reason for differences in sens itivity to chlorsulfuron between the wheat cultivars tested.