Frequency of Gly-210 Deletion Mutation among Protoporphyrinogen Oxidase Inhibitor–Resistant Palmer Amaranth (Amaranthus palmeri) Populations

Abstract

The widespread occurrence of Palmer amaranth resistant to acetolactate synthase inhibitors and/or glyphosate led to the increased use of protoporphyrinogen oxidase (PPO)-inhibiting herbicides. This research aimed to: (1) evaluate the efficacy of foliar-applied fomesafen to Palmer amaranth, (2) evaluate cross-resistance to foliar PPO inhibitors and efficacy of foliar herbicides with different mechanisms of action, (3) survey the occurrence of the PPO Gly-210 deletion mutation among PPO inhibitor–resistant Palmer amaranth, (4) identify other PPO target-site mutations in resistant individuals, and (5) determine the resistance level in resistant accessions with or without the PPO Gly-210 deletion. Seedlings were sprayed with fomesafen (263 gaiha−1), dicamba (280 gaiha−1), glyphosate (870 gaiha−1), glufosinate (549 g ai ha−1), and trifloxysulfuron (7.84 gaiha−1). Selected fomesafen-resistant accessions were sprayed with other foliar-applied PPO herbicides. Mortality and injury were evaluated 21 d after treatment (DAT). The PPX2L gene of resistant and susceptible plants from a selected accession was sequenced. The majority (70%) of samples from putative PPO-resistant populations in 2015 were confirmed resistant to foliar-applied fomesafen. The efficacy of other foliar PPO herbicides on fomesafen-resistant accessions was saflufenacil>acifluorfen=flumioxazin>carfentrazone=lactofen>pyraflufen-ethyl>fomesafen>fluthiacet-methyl. With small seedlings, cross-resistance occurred with all foliar-applied PPO herbicides except saflufenacil (i.e., 25% with acifluorfen, 42% with flumioxazin). Thirty-two percent of PPO-resistant accessions were multiple resistant to glyphosate and trifloxysulfuron. Resistance to PPO herbicides in Palmer amaranth occurred in at least 13 counties in Arkansas. Of 316 fomesafen survivors tested, 55% carried the PPO Gly-210 deletion reported previously in common waterhemp. The PPO gene (PPX2L) in one accession (15CRI-B), which did not encode the Gly-210 deletion, encoded an Arg-128-Gly substitution. The 50% growth reduction values for fomesafen in accessions with Gly-210 deletion were 8- to 15-fold higher than that of a susceptible population, and 3- to 10-fold higher in accessions without the Gly-210 deletion.

First evidence of multiple resistance of Sumatran Fleabane (Conyza sumatrensis (Retz.) E.Walker) to five- mode-of-action herbicides

“…The resistance mechanism to saflufenacil remains unknown, but resistance to PPOherbicides in Amaranthus spp. was attributed to a target-site mutation in the PPX2 gene only, characterized by a Gly-210 deletion (Patzoldt et al, 2006, Salas et al, 2016Salas-Perez et al, 2017). PSII inhibitors block electron transfer to the secondary QB plastoquinone (QB-site) acceptor of the D1 subunit protein, resulting in interruption of electron transfer from the primary plastoquinone site (QA-site) to QB (Powles and Yu, 2010).…”

The challenge of herbicide resistance around the world: a current summary

“…140 PPO-resistant biotypes of A. palmeri have also been discovered across much of the mid-South in states such as Arkansas and Tennessee. 141,142 Resistance in these biotypes tends to be more strongly exhibited to foliar applications of PPO herbicides compared with soil-applied products within the same SOA, with lower resistance ratios for the soil-applied materials. 143 This may be mainly due to the relatively high dose of soil-applied products made to ensure sufficient length of residual control.…”

“…Results from 593 field samples of A. tuberculatus and A. palmeri collected in 10 Midwestern states indicated as many as 82% testing positive for both GR and PPO resistance, depending on the state . PPO‐resistant biotypes of A. palmeri have also been discovered across much of the mid‐South in states such as Arkansas and Tennessee . Resistance in these biotypes tends to be more strongly exhibited to foliar applications of PPO herbicides compared with soil‐applied products within the same SOA, with lower resistance ratios for the soil‐applied materials .…”

“…As glyphosate failed, farmers who simply moved to the next best alternative herbicide without implementing other diversification tactics often saw development of resistance to the alternative herbicide and more multiple‐resistant populations in their fields. Recent increases in Amaranthus populations with resistance to both glyphosate and PPO herbicides are prime examples of this sequence of events . In some crops such as soybeans, the herbicide options for foliar control of some species have narrowed sharply.…”

“…Recent increases in Amaranthus populations with resistance to both glyphosate and PPO herbicides are prime examples of this sequence of events. 140,141 In some crops such as soybeans, the herbicide options for foliar control of some species have narrowed sharply. New herbicide-tolerant soybeans and cotton enable use of auxin herbicides (i.e.…”