PPO2 Mutations in Amaranthus palmeri: Implications on Cross-Resistance

Abstract

In Arkansas, resistance to protoporphyrinogen IX oxidase (PPO)-inhibiting herbicides in Amaranthus palmeri S. Wats. is mainly due to target site mutations. Although A. palmeri PPO-mutations are well investigated, the cross-resistance that each ppo mutant endows to weed populations is not yet well understood. We aimed to evaluate the response of PPO-resistant A. palmeri accessions, harboring the ppo2 mutations ΔG210 and G399A, to multiple PPO-inhibiting herbicides. Six resistant and one susceptible field accessions were subjected to a dose–response assay with fomesafen, and selected survivors from different fomesafen doses were genotyped to characterize the mutation profile. The level of resistance to fomesafen was determined and a cross-resistance assay was conducted with 1 and 2 times the labeled doses of selected PPO herbicides. The accession with higher predicted dose to control 50% of the population (ED50) had a higher frequency of ΔG210-homozygous survivors. Survivors harboring both mutations, and those that were ΔG210-homozygous, incurred less injury at the highest fomesafen rate tested (1120 g ai ha−1). The populations with a high frequency of ΔG210-homozygous survivors, and those with individuals harboring ΔG210 + G399A mutations, exhibited high potential for cross-resistance to other PPO herbicides. The new PPO–herbicide chemistries (saflufenacil, trifludimoxazin) generally controlled the PPO-resistant populations.

Microencapsulation of High‐Content Actives Using Biodegradable Silk Materials

“…This method is widely used across the agricultural industry for both greenhouse and field trials to determine the amount of injury that is present to the desired crop plant after a chemical application. [50,51] Corn crop response from herbicide applications consisted of necrotic spots on foliage exposed at the time of application. In Figure 4c, the experimental treatment SF/Saf-MSO resulted in significantly lower crop response compared to the standard Sharpen-MSO treatment, hence demonstrating improved crop safety with POST applications.…”

Field-Evolved ΔG210-ppo2 from Palmer Amaranth Confers Pre-emergence Tolerance to PPO-Inhibitors in Rice and Arabidopsis

“…Even though the transgene presence provided tolerance to foliar- and soil-applied fomesafen, plants displayed variable tolerance to fomesafen, which could be due to varying levels of transgene expression with the presence of hemizygous vs. homozygous states of the transgene. In PPO-resistant A. palmeri , Carvalho-Moore et al [ 49 ] showed that among the resistant accessions tested, the accession with a high frequency of survivors that are homozygous for Δ G210 also had higher ED50 and less injury at a high dose of fomesafen. Variation in transgene expression is expected in the progeny since transgenic individuals generally differ in transgene expression, and full or partial levels of gene expression may be heritable [ 50 ].…”

Design, synthesis and screening of herbicidal activity for new phenyl pyrazole‐based protoporphyrinogen oxidase‐inhibitors (PPO) overcoming resistance issues

“…In 2001, waterhemp was the first weed reported to evolve resistance to PPO herbicides, which was via the mechanism of the deletion of PPO2 glycine at position 210 (ΔG210) in the capping region of the a8 helix of extended mitochondrial isoform, PPx2L, which resulted in a change in the binding pocket 19,20 . The same mutation for Palmer amaranth was discovered later 13–15,21 . Additional herbicide‐resistant mechanisms for Palmer amaranth recently have been discovered, with two mutations found in the PPO2 enzyme in the R128 site (R128G or R128M) and a substitution of amino acid glycine for alanine in the catalytic domain of PPO2 at position 399 (G399A) 14,21,22 .…”

“…[13][14][15]21 Additional herbicide-resistant mechanisms for Palmer amaranth recently have been discovered, with two mutations found in the PPO2 enzyme in the R128 site (R128G or R128M) and a substitution of amino acid glycine for alanine in the catalytic domain of PPO2 at position 399 (G399A). 14,21,22 A nontarget-site resistance mechanism also has been reported for Palmer amaranth, which involves metabolizing and detoxifying the herbicide via cytochrome P450 monooxygenase and glutathione S-transferase activity. 18 A nontarget-site resistant population of waterhemp also has been reported recently, yet further research on this mechanism is still needed.…”