Coevolution of resistance to PPO inhibitors in waterhemp (Amaranthus tuberculatus) and Palmer amaranth (Amaranthus palmeri). Issue 5 (September 2019)

• Record Type: Journal Article
• Authors: Lillie, Kathryn J.; Giacomini, Darci A.; Green, Jonathan D.; Tranel, Patrick J.
• Is Part Of: Weed science. Volume 67:Issue 5(2019)
• Page Start: 521
• Page End: 526
• Publication Date: 2019-09
• Subjects: Ramon G. Leon, North Carolina State University; Convergent evolution, -- herbicide resistance, -- parallel evolution, -- protoporphyrinogen oxidase.; 632.505
• DOI: 10.1017/wsc.2019.41
• Languages: English
• ISSNs: 0043-1745

Abstract

Abstract: The first case of evolved protoporphyrinogen oxidase (PPO)-inhibitor resistance was observed in 2001 in common waterhemp [ Amaranthus tuberculatus (Moq.) Sauer var. rudis (Sauer) Costea and Tardif]. This resistance in A. tuberculatus is most commonly conferred by deletion of the amino acid glycine at the 210th position (ΔGly-210) of the PPO enzyme (PPO2) encoded by PPX2 . In a field in Kentucky in 2015, inadequate control of Amaranthus plants was observed following application of a PPO inhibitor. Morphological observations indicated that survivors included both A. tuberculatus and Palmer amaranth ( Amaranthus palmeri S. Watson). Research was conducted to confirm species identities and resistance and then to determine whether resistance evolved independently in the two species or via hybridization. Results from a quantitative PCR assay based on the ribosomal internal transcribed spacer confirmed that both A. tuberculatus and A. palmeri coexisted in the field. The mutation conferring ΔGly-210 in PPO2 was identified in both species; phylogenetic analysis of a region of PPX2, however, indicated that the mutation evolved independently in the two species. Genotyping of greenhouse-grown plants that survived lactofen indicated that all A. tuberculatus survivors, but only a third of A. palmeri survivors, contained the ΔGly-210 mutation. Consequently, A. palmeri plants were evaluated for the presence of an arginine to glycine or methionine substitution at position 128 of PPO2 (Arg-128-Gly and Arg-128-Met). The Arg-128-Gly substitution was found to account for resistance that was not accounted for by the ΔGly-210 mutation in plants from the A. palmeri population. Results from this study provide a modern-day example of both parallel and convergent evolution occurring within a single field.