Comparing responses of sensitive and resistant populations of Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus tuberculatus var. rudis) to PPO inhibitors

Abstract

Resistance to protoporphyrinogen oxidase (PPO) inhibitors was first observed in waterhemp in 2001 and was conferred by the deletion of a glycine residue at the 210th position (ΔGly-210) of the PPO enzyme. PPO-inhibitor resistance in Palmer amaranth was first observed in 2011, 10 years later. The objectives of this study were to directly compare PPO inhibitor responses in plants of both species with or without the ΔGly-210 mutation. Using greenhouse experiments, early (EPOST) and late (LPOST) postemergence dose responses using lactofen and fomesafen, and preemergence (PRE) dose responses using fomesafen and flumioxazin, were obtained for a sensitive and resistant population each of waterhemp and Palmer amaranth. An additional spray study confirmed each sensitive population used in the dose responses was representative of its respective species, with regards to PPO-inhibitor sensitivity. When treated at either POST timing, Palmer amaranth was more tolerant than waterhemp, and the ΔGly-210 mutation provided greater resistance in Palmer amaranth (48-fold to >3,440-fold, depending on timing and herbicide) than in waterhemp (31-fold to 123-fold). The level of tolerance in Palmer amaranth was striking; the sensitive Palmer amaranth population treated LPOST survived as well or better than the resistant waterhemp population treated EPOST. With PRE applications, response differences both between species and between resistant and sensitive populations generally were less pronounced, relative to POST applications. Collectively, this research indicates Palmer amaranth tolerance to POST-applied PPO inhibitors could have initially slowed (relative to waterhemp) evolution of resistance to these herbicides, and resistant and sensitive populations of both species are more likely to be effectively controlled with PRE rather than POST applications.

Coexpression Clusters and Allele-Specific Expression in Metabolism-Based Herbicide Resistance

“…2012 ). Herbicide-resistant plants from each population were crossed with an herbicide-sensitive A. tuberculatus population (WUS; originally collected in Brown County, OH) and F 1 seeds were screened to confirm resistance to both HPPD inhibitors and 2,4-D. To screen these F 1 populations, plants were grown under previously described greenhouse conditions ( Lillie et al. 2020 ) and sprayed with an initial discriminating dose of mesotrione (220 g ai ha −1 ; Callisto; Syngenta Crop Protection Inc., Greensboro, NC) plus 1% v/v crop oil concentrate, followed by a late POST treatment of 2,4-D (560 g ae ha −1 ; 2,4-D amine; Nufarm Americas Inc., Chicago, IL) plus 0.25% v/v nonionic surfactant.…”

“…2020 ) and sprayed with an initial discriminating dose of mesotrione (220 g ai ha −1 ; Callisto; Syngenta Crop Protection Inc., Greensboro, NC) plus 1% v/v crop oil concentrate, followed by a late POST treatment of 2,4-D (560 g ae ha −1 ; 2,4-D amine; Nufarm Americas Inc., Chicago, IL) plus 0.25% v/v nonionic surfactant. All herbicide applications were made using a moving-nozzle spray chamber as described previously ( Lillie et al. 2020 ).…”

Herbicide resistance in Amaranthus tuberculatus†

“…Further work has conclusively demonstrated, however, that plants with ΔG210 are less sensitive to PPO inhibitors regardless of the application timing. [51][52][53] A typical field use rate of a preemergence PPO inhibitor is sufficient to control resistant individuals that emerge within a few days after application (assuming appropriate rainfall for herbicide activity). However, as the herbicide concentration near the soil surface decreases over time (due to degradation, leaching, and diffusion), it will reach a point at which it is still sufficient to control an emerging cohort of sensitive individuals, but not resistant individuals.…”

“…PPO inhibitors applied preemergence were reported to provide effective control of A. tuberculatus populations that were resistant to these same herbicides applied postemergence, 50 leading to the misconception (which still persists) that the PPO G210 deletion confers resistance to PPO inhibitors applied postemergence but not preemergence. Further work has conclusively demonstrated, however, that plants with ΔG210 are less sensitive to PPO inhibitors regardless of the application timing 51–53 . A typical field use rate of a preemergence PPO inhibitor is sufficient to control resistant individuals that emerge within a few days after application (assuming appropriate rainfall for herbicide activity).…”

Valent USA LLC strategies, innovations, and collaborations to deal with herbicide resistance and achieve sustainability

“…Through a partnership with the University of Illinois, Valent has provided support in the surveying and understanding the spread of PPO resistance in the Amaranthus spp. In order to better understand PPO resistance in terms of mechanism(s), spread, differences in PPO resistance between species, and the development of a rapid detection method, Valent has sponsored research with the University of Illinois and Colorado State University 11‐13 …”