Target and Nontarget Resistance Mechanisms Induce Annual Bluegrass (Poa annua) Resistance to Atrazine, Amicarbazone, and Diuron

Abstract

Annual bluegrass is a weed species in turfgrass environments known for exhibiting resistance to multiple herbicide modes of action, including photosystem II (PSII) inhibitors. To evaluate populations of annual bluegrass for susceptibility to PSII inhibitors of varied chemistries, populations were treated with herbicides from triazolinone, triazine, and substituted urea families: amicarbazone, atrazine, and diuron, respectively. Sequencing of thepsbAgene confirmed the presence of a Ser264to Gly amino acid substitution within populations that exhibited resistance to both atrazine and amicarbazone. A single biotype, DR3, which lacked any previously reportedpsbAgene point mutation, exhibited resistance to diuron, atrazine, and amicarbazone. DR3 had a significantly lower rate of absorption and translocation of atrazine and had enhanced atrazine metabolism when compared with both the Ser264to Gly resistant mutant and susceptible biotypes. We thus report possible nontarget mechanisms of resistance to PSII-inhibiting herbicides in annual bluegrass.