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R128L Target Site Mutation in PPO2 Evolves in Wild Poinsettia (Euphorbia heterophylla) with Cross-Resistance to PPO-Inhibiting Herbicides

  • Rafael R Mendes (a1), Hudson K Takano (a2), Fernando S Adegas (a3), Rubem S Oliveira (a4), Todd A Gaines (a5) and Franck E Dayan (a6)...

Abstract

Wild poinsettia (Euphorbia heterophylla L.) is a troublesome broadleaf weed in grain production areas from South America. Herbicide resistance to multiple sites of action has been documented in this species, including protoporphyrinogen oxidase (PPO) inhibitors. We investigated the physiological and molecular bases for PPO resistance in a E. heterophylla population (R-PPO) from Southern Brazil. Whole-plant dose response experiments revealed a cross resistance profile to three different chemical groups of PPO inhibitors. Based on dose response parameters, R-PPO was resistant to lactofen (47.7-fold), saflufenacil (8.6-fold), and pyraflufen-ethyl (3.5-fold). Twenty-four h after lactofen treatment (120 g ha-1) in POST, R-PPO accumulated 27 times less protoporphyrin than the susceptible population (S-PPO). In addition, R-PPO generated 5 and 4.5 times less hydrogen peroxide and superoxide than S-PPO, respectively. The chloroplast PPO (PPO1) sequences were identical between the two populations, whereas 35 single nucleotide polymorphisms were found for the mitochondrial PPO (PPO2). Based on protein homology modeling, the R128L (homologous to R98L in common ragweed (Ambrosia artemisiifolia L.) was the only one located near the catalytic site, also in a conserved region of PPO2. The cytochrome P450 monooxygenase inhibitor malathion did not reverse resistance to lactofen in R-PPO, and both populations showed similar levels of PPO1 and PPO2 expression, suggesting that metabolic resistance and PPO overexpression are unlikely. This is the first report of a R128L mutation in PPO2 conferring cross resistance to PPO inhibitors in E. heterophylla.

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Corresponding author

Author for correspondence: Franck E Dayan, Professor, Colorado State University, Agricultural Biology, 1177 Campus Delivery, Fort Collins, CO, USA. (E-mail: franck.dayan@colostate.edu)

Keywords

R128L Target Site Mutation in PPO2 Evolves in Wild Poinsettia (Euphorbia heterophylla) with Cross-Resistance to PPO-Inhibiting Herbicides

  • Rafael R Mendes (a1), Hudson K Takano (a2), Fernando S Adegas (a3), Rubem S Oliveira (a4), Todd A Gaines (a5) and Franck E Dayan (a6)...

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