Selection of atrazine tolerant soybean calli and expression of that tolerance in regenerated plants.

Lines of soybean [Glycine max (L.)] tolerant of atrazine were developed by an in vitro and in vivo atrazine challenge. Cotyledonary node plus epicotyl explants from mature germinated seed of soybean introduction PI 438489B were cultured on RV-5 medium containing 48 mg active ingredient (a.i.)/l atrazine for one month. Most of the explants (66%) on medium containing atrazine, and 10% on medium without atrazine died. Explants surviving exposure to atrazine callused and organogenically regenerated shoots developed. Soil around R0 plants regenerated from atrazine tolerant shoots and nonatrazine challenged shoots (controls) were subsequently tested in vivo for atrazine tolerance. All controls died. Seeds were collected from atrazine tolerant R0 plants. Two weeks after planting, emerged R1 seedlings were tested in vivo for atrazine tolerance as the R0 plants were. This procedure was repeated on the R2 plants. All nonatrazine selected control plants died when exposed to this herbicide. Atrazine tolerant R2 plants were maintained in atrazine amended soil and appeared as healthy and vigorous as the control growing in atrazine free soil.