This study documents the physiology and genetics of evolved atrazine resistance in a wild radish population from Western Australia. Plant response to atrazine treatment confirmed a high level of resistance in population WARR5. At 0.25 kg atrazine/ha, all plants from a susceptible population were killed, whereas resistant WARR5 was unaffected at the highest dose tested (4 kg atrazine/ha). Leaf photosynthesis in susceptible plants was inhibited after 1 kg atrazine/ha treatment, whereas leaf photosynthesis in WARR5 plants was unaffected. Furthermore, atrazine resistance was maternally inherited. Sequencing of a psbA gene fragment in resistant WARR5 and susceptible plants revealed a single point mutation resulting in a coding change from Ser₂₆₄ to Gly of the D1 protein in resistant plants. We are confident that this mutation is the basis of resistance to the photosystem II inhibitors in this wild radish population.

Nomenclature: Atrazine; metribuzin; wild radish, Raphanus raphanistrum L. RAPRA.