Two new PPX2 mutations associated with resistance to PPO-inhibiting herbicides in Amaranthus palmeri

BACKGROUND Resistance to herbicides that inhibit protoporphyrinogen oxidase (PPO) is a widespread and growing problem for weed managers across the midwestern and midsouthern United States. In Amaranthus spp., this resistance is known to be conferred by a glycine deletion at the 210th amino acid (ΔG210) in PPO2. Preliminary analysis indicated that the ΔG210 mutation did not fully account for observed resistance to PPO inhibitors in two Amaranthus palmeri populations from Tennessee and one from Arkansas. RESULTS Sequencing PPX2 cDNA from six resistant plants uncovered two new mutations at the R98 site (R98G and R98M), a site previously found to endow PPO-inhibitor resistance in Ambrosia artemisiifolia. Sequencing of this region from additional plants sprayed with 264 g fomesafen ha−1 showed the presence of one or both R98 mutations in a subset of the resistant plants from all three populations. No plants sensitive to fomesafen contained either mutation. A derived cleaved amplified polymorphic sequence (dCAPS) assay to test for the presence of these mutations in A. palmeri was developed. CONCLUSION Two new mutations of PPX2 (R98G, R98M) likely confer resistance to PPO-inhibitors in A. palmeri, and can be rapidly identified using a dCAPS assay. © 2017 Society of Chemical Industry