Recovery of Imidazolinone‐Resistant Hard Red Wheat Lines Following Imazamox Application

Imidazolinone‐resistant hard red wheat ( Triticum aestivum L.) cultivars are occasionally injured by imazamox applications because a portion of the acetolactate synthase (ALS) remains susceptible to the herbicide. The growth and enzyme activity of two groups of hard red wheat near‐isolines with spring or winter growth habit were examined following imazamox application. Each group of near‐isolines contained a susceptible cultivar and cultivars with the imidazolinone‐resistant trait on either the B or D genome. The spring wheat group also contained a line carrying both the B and D genome copies of the resistance gene. In whole plant experiments, growth of all single‐gene resistant lines was delayed by both 35 and 105 g ha −1 imazamox while the two‐gene line was delayed at only the highest rate. There was a herbicide rate effect on biomass accumulation but no differences among genome locations in the single‐gene resistant lines or among spring vs. winter growth habit. On an ALS enzyme basis, however, there were differences among B‐ vs. D‐genome resistance and between winter and spring growth habit. Spring wheat cultivars with the B‐genome resistance had greater reductions in ALS activity compared to the D‐genome cultivars, while in winter wheat, B‐ and D‐genome lines responded similarly. Differences among genotypes existed in the recovery of ALS activity in imidazolinone wheat but other factors also likely influence the injury occasionally observed in the field.