FATE OF ATRAZINE IN TREATED AND PRISTINE ACCESSIONS OF 3 SETARIA SPECIES

Three species of Setaria have a modicum of resistance to atrazine in S pain. Two of them, Setaria adherens and Setaria verticillata are natur ally resistant to field levels of atrazine and are 12 times more resis tant than wild-type Setaria glauca. S. glauca evolved a >700-fold incr ease in resistance under continuous atrazine treatment in monoculture maize. Only the S. glauca R biotype plastids had less affinity for atr azine than those of its susceptible (S) biotype based on chlorophyll f luorescence (both intensity and fast fluorescence). As expected, it ex hibited cross-resistance to a wide variety of PS II inhibitors. Conver sely, S. adherens and S. verticillata leaves from habitats with monocu lture maize as well as pristine habitats conjugated >80% of the atrazi ne while both S. glauca biotypes conjugated <20% of the atrazine. S. a dherens leaves conjugated atrazine much better than simazine and propa zine, and no other PS II herbicides were tested. The specific glutathi one transferase for atrazine had a 1.5 times greater activity in the S . verticillata than in the Setaria glauca, which may be the cause of t he enhanced metabolism. (C) 1996 Academic Press.