Mutations inALSconfer herbicide resistance in redroot pigweed (Amaranthus retroflexus) and Powell amaranth (Amaranthus powellii)

Abstract

A number of redroot pigweed and Powell amaranth populations from various locations in Ontario, Canada, have distinct patterns of resistance to the acetolactate synthase–inhibiting herbicides imazethapyr and thifensulfuron. This suggested the presence of diverse ALS gene mutations among these populations. Seven polymerase chain reaction primer pairs were used to amplify the gene to obtain full sequence information and to determine the identity of resistance-conferring mutations. There was a high degree of similarity in the ALS gene of the two species with only five nucleotides and one amino acid differing. A total of four herbicide resistance-conferring mutations were identified in the two species. The Ala122Thr, Ala205Val, and Trp574Leu amino acid substitutions were found in redroot pigweed whereas Ala122Thr, Trp574Leu, and Ser653Thr were detected in Powell amaranth. The pattern of resistance known to be conferred by the mutations concurred with the resistance level observed at the whole plant level. Distinct mutations being found in geographically separated populations suggest that selection for resistance occurred simultaneously in different locations. It reinforces the fact that resistance to ALS inhibitors is easily selected and that growers need to take this into account when formulating weed management strategies.

Acetolactate synthase mutation conferring imidazolinone-specific herbicide resistance in Amaranthus hybridus

“…2). This mutation has been identified as the basis for ALS-inhibitor resistance in three other weedy species: Xanthium strumarium L. (Bernasconi et al, 1995), Solanum ptycanthum Dun (Milliman et al, 2003), and A. retroflexus L. (McNaughton et al, 2005). Since the entire gene was not sequenced, it is possible that additional polymorphisms may exist between the resistant and susceptible enzymes.…”

The biology of Canadian weeds. 130. Amaranthus retroflexus L., A. powellii S. Watson and A. hybridus L.

“…Resistance to ALS-inhibiting herbicides is due to target site mutations, which result in the production of an ALS enzyme with decreased sensitivity to these herbicides (reviewed by Saari et al 1994;McNaughton et al 2001). The resistance trait is controlled by a single nuclear gene with incomplete dominance.…”

Florida beggarweed (Desmodium tortuosum) management in peanut (Arachis hypogaea) with residual herbicides

“…If ALS resistance does develop in Florida beggarweed, it will likely occur as a result of these types of control methods. Weed resistance to ALS herbicides occurs because of the repetitive use of this mode of action in multiple crops, and the ability of different mutations to hinder herbicide binding (McNaughton et al 2005;Tranel and Wright 2002). For this study, chlorimuron did reduce Florida beggarweed biomass but it did not reduce the populations.…”