Multiple resistance to imazethapyr and atrazine in Powell amaranth (Amaranthus powellii)

Abstract

Multiple-herbicide resistance represents an added weed management challenge to growers as it can considerably reduce their options for weed control. The widespread nature of triazine resistance in Ontario coupled with the more recent appearance of resistance to ALS inhibitors in Amaranthus species warranted documenting biotypes with multiple resistance. A collection of Powell amaranth and redroot pigweed biotypes that had previously been characterized for resistance to ALS inhibitors was therefore screened with atrazine. Dose–response analysis with atrazine and imazethapyr was also conducted. High-level resistance to imazethapyr and atrazine was determined in a Powell amaranth biotype from Perth County, Ontario. This biotype had a > 1,860-fold and 109-fold resistance to atrazine and imazethapyr, respectively. Sequence analysis was conducted for the psbA and ALS genes that code for the target sites of the triazines and imidazolinones, respectively. A mutation in the psbA gene was identified that coded for an amino acid substitution of glycine for serine at residue 264 of the D1 protein. This mutation is the most likely cause for triazine resistance in this biotype. Similarly, a nucleotide substitution was identified that codes for threonine in place of serine at position 652 of the ALS protein. This mutation in the ALS gene has only been observed previously in laboratory-selected mutants of arabidopsis and tobacco and is known to endow resistance to imidazolinones in plants. It is concluded that multiple resistance in this Powell amaranth biotype is due to the presence of altered target sites for triazine and imidazolinone herbicides.

Nontarget-Site Resistance to ALS Inhibitors in Waterhemp (Amaranthus tuberculatus)

“…The six amino acid substitutions identified in JG11 were shared among the plants sequenced (although the zygosity of each substitution was different among plants) but nevertheless are unlikely to be responsible for resistance: these same substitutions relative to WCS were identified in ACR and IR-101. In addition, these amino acid substitutions were observed in other weed species as well, in both resistant and susceptible biotypes, suggesting that they are in nonconserved regions of ALS and not associated with herbicide resistance (Diebold et al 2003;McNaughton et al 2005;Patzoldt and Tranel 2007).…”

Rapid bidirectional allele‐specific PCR identification for triazine resistance in higher plants

“…Since its discovery in Amaranthus hybridus L.,5 the sole mutation Ser 264 –Gly has been found in nearly all the spontaneous field herbicide‐resistant mutants analysed so far (Table 1). 5–34 There were two exceptions, namely a Ser–Thr mutation at the same residue 26435 and a Val–Ile mutation at residue 219 36…”

Management of Pigweed (Amaranthusspp.) in Glufosinate-Resistant Soybean in the Midwest and Mid-South

“…), and redroot pigweed (Amaranthus retroflexus L.) are highly competitive broadleaf weed species that are becoming increasingly troublesome to manage in agricultural production systems. This is due to exceedingly high growth rates and development plasticity (Horak and Loughin 2000), prolific seed production (Sellers et al 2003), and an ability to rapidly evolve resistance to multiple herbicide sites of action (Bell et al 2013;Culpepper et al 2006;Diebold et al 2003;Heap 2014). Once pigweeds infest soybean fields, interference has shown to reduce soybean grain yield by up to 78% (Bensch et al 2003).…”