ALS inhibitor resistance in populations of Powell amaranth and redroot pigweed

Abstract

In 1997, farmers in Ontario, Canada, reported failure of some ALS-inhibiting herbicides to provide adequate control of pigweed species. Growth room experiments were conducted to confirm resistance to ALS inhibitors in populations of Powell amaranth and redroot pigweed. Twenty-two out of 35 collected seed samples were able to grow in the presence of soil-applied imazethapyr or flumetsulam. Dose–response curves were generated for 11 and 9 populations of Powell amaranth and redroot pigweed, respectively, using foliar-applied imazethapyr and thifensulfuron. Resistance to ALS inhibitors was confirmed in nine and five populations of Powell amaranth and redroot pigweed, respectively. Within each species, comparison of the herbicide rate required to reduce plant dry weight 50% (GR50) between the resistant populations and a susceptible population was conducted to obtain resistance factors. For imazethapyr, resistance factors ranged from 4.2 to 3,438 and from 33 to 168 for Powell amaranth and redroot pigweed, respectively. High-level cross-resistance to thifensulfuron was found in two populations of each species, with resistance factors ranging from 270 to 2,416. In both species, populations could be grouped according to their cross-resistance patterns: some populations were resistant to imazethapyr only, whereas others expressed resistance to both imazethapyr and thifensulfuron. The observed patterns of cross-resistance were not correlated with known herbicide exposure history of the fields where these populations originated.

Glyphosate-resistant Canada fleabane [Conyza canadensis (L). Cronq.]: Dose response to glyphosate and control with postemergence herbicides in soybean in Ontario

“…Resistance factors in previous studies range from 4 to 13) compared with susceptible populations (VanGessel 2000;Koger et al 2004;Zelaya et al 2004). This, however, is low compared with reports of ALS inhibitor resistance indices of up to 3438) compared with susceptible (Ferguson et al 2001). Even though the resistance indices for previously reported GR Canada fleabane are low compared with the ALS inhibitors, the dose of glyphosate required for control of GR Canada fleabane is still not economically feasible (Hanson et al 2009 (1 for the control of the heterozygous and homozygous resistant biotypes, respectively.…”

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

“…In Ontario, A. retroflexus and A. powellii were among the first weeds to develop resistance to triazine herbicides, which inhibit photosystem II (Warwick and Weaver 1980). Later, they were the first weed species in Ontario to develop resistance to herbicides that inhibit the enzyme acetolactate synthase (ALS) (Ferguson et al 2001). Resistant plants cannot be distinguished visually from susceptible ones.…”

Comparative analysis of the anatomy of two populations of red-root amaranth (Amaranthus retroflexus L.)

“…This has been confirmed for a great number of amaranth species, such as: Amaranthus palmeri (Gaeddert et al, 1997), A. retroflexus (Ferguson et al, 2001), A. blitoides (Sibony and Rubin, 2003), A. rudis (Lovell et al, 1996), A. hybridus (Maertens et al, 2004) and A. powellii (Ferguson et al, 2001). Tardif et al (2006) attempted to determine a relationship between mutation that causes resistance to herbicides ALS-inhibitors, and morphological and histological characteristics of the species A. powellii, but could not identify a distinct connection between the Trp574Leu substitution on the ALS enzyme and plant morphology and anatomy of resistant populations.…”