Absorption, Translocation, and Metabolism of Mesotrione in Grain Sorghum

Studies were conducted under controlled growth conditions to determine whether differential absorption, translocation, or metabolism was the basis for the differential response of grain sorghum hybrids to mesotrione. Mesotrione-tolerant ('Dekalb DKS35-70') and mesotrione-susceptible ('Pioneer 84G62') grain sorghum hybrids were treated with C-14-labeled mesotrione. At 1 d after treatment (DAT), absorption was 7% in both hybrids; at 7 DAT, however, absorption remained nearly steady in Pioneer 84G62 but increased to 12% in Dekalb DKS35-70. Translocation of C-14-mesotrione in sorghum hybrids was similar with less than 30% of the absorbed herbicide translocated out of the treated leaf by 7 DAT. A distinct metabolite of C-14-mesotrione was separated in both hybrids at 3 DAT. The amount of mesotrione parent compound that remained in Pioneer 84G62 and DKS35-70 was 72 and 65%, respectively. Dekalb DKS35-70 had significantly less mesotrione at 3 DAT than Pioneer 84G62 did, but the amount of mesotrione was similar for both hybrids at 5 and 7 DAT. Rapid metabolism of mesotrione may help explain the differential response of grain sorghum hybrids.