Document Type
Article
Publication Date
2-2023
Keywords
Pre-emergence herbicide resistance; PPO inhibitors; PPO2 gene
Abstract
Resistance to protoporphyrinogen oxidase (PPO) inhibitors in Palmer amaranth is a major concern, given the high selection pressure and increasing number of populations with reduced sensitivity to PPO herbicides in the US. We evaluated the effect of five soil-applied herbicides on Palmer amaranth (Amaranthus palmeri S. Wats.) populations collected in 2014 and 2015 in Arkansas, USA. Soil-applied saflufenacil, sulfentrazone, and flumioxazin reduced the seedling emergence 91–100%; however, fomesafen and oxyfluorfen showed reduced (63–90%) efficacy on some populations. Target-site mutation (TSM) is the major mechanism of resistance to PPO herbicides; therefore, six populations showing resistance to soil-applied fomesafen were selected for molecular investigations. A total of 81 survivors were genotyped for all known resistance-conferring mutations. A total of 64% and 36% survivors had single and double TSMs, respectively, with 69% of plants carrying TSM in both alleles of PPO2. Three survivors from two populations showed an additional copy of PPO2, whereas all other survivors had one copy. Expression analysis showed 3- to 6-fold upregulation of PPO2 in all plants from resistant populations tested. Transgenic overexpression of WT-ApPPO2 and dG210-Apppo2 in A. thaliana confirmed the reduced sensitivity to soil-applied fomesafen compared to the wild type. Collectively, PPO inhibitors applied pre-emergence are still effective in controlling populations resistant to foliar-applied PPO herbicides. Mechanically, elevated expression of resistant PPO2, alongside functional TSM, contribute to reduced sensitivity to soil-applied fomesafen.
Citation
Rangani, G.; Porri, A.; Salas-Perez, R.A.; Lerchl, J.; Karaikal, S.K.; Velásquez, J.C.; Roma-Burgos, N. Assessment of Efficacy and Mechanism of Resistance to Soil-Applied PPO Inhibitors in Amaranthus palmeri. Agronomy 2023, 13, 592. https://doi.org/10.3390/agronomy13020592
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This work is licensed under a Creative Commons Attribution 4.0 International License.
Comments
Supplementary Materials
The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy13020592/s1, Figure S1: Copy number of PPO2 gene in survivors from 1x soil-applied fomesafen treatment; Table S1: Common, trade names, and manufacturers of herbicides used in the study; Table S2: List of primers used in the copy number and expression assay; Table S3: Comparison of frequency of two resistant allele with the frequency of survivors to soil-applied fomesafen (1x) among six resistant A. palmeri population; Table S4: Comparison between frequency of survivors with foliar- and soil-applied fomesafen (1x).