Response of heterozygous and homozygous Imidazolinone-resistant spring wheat genotypes to Imazamox
Imidazolinone-resistant (IR) spring wheat (Triticum aestivum L.) was released commercially in Canada in 2004, providing growers with a new opportunity to selectively control a broad range of weeds in wheat, including volunteer cereals and annual grasses. Imidazolinone (IMI) herbicides inhibit acetolactate synthase in susceptible (S) plants, but IR wheat plants have an altered target site that confers resistance to IMI herbicides. The IR trait has served as a phenotypic marker in a number of gene flow studies, but the response of IR F1 wheat hybrids to various doses of imazamox has not been adequately characterized. Therefore, a greenhouse study was initiated to assess the whole-plant response of several spring wheat genotypes with different parental backgrounds to increasing doses of imazamox. No differences in biomass accumulation prior to imazamox application were detected among genotypes. Biomass accumulation after foliar treatment with imazamox was similar within all groups of genotypes, with no significant differences detected within F1 or S genotype groups. The resistance factor (GR50 ratio) of the single IR genotype tested in the study was six-fold greater than the mean of the F1 genotypes, which was itself six-fold greater than that of the S genotypes examined. Differential mortality was observed between some S genotypes at 3.9 g a.i. ha–1, but no differences between genotypes were observed at any other dose. The results of this study indicate that for the spring wheat genotypes assessed, parental background and market class do not affect spring wheat tolerance to imazamox. Furthermore, results indicate that the IR trait in spring wheat should provide a satisfactory marker for pollen-mediated gene flow studies.