A family affair: resistance mechanism and alternative control of three Amaranthus species resistant to acetolactate synthase inhibitors in Italy

Abstract

BACKGROUND Several soybean fields in Italy were found to be infested by multiple species of Amaranthus spp. not adequately controlled by acetolactate (ALS) inhibitor herbicides. The objectives of this research were (i) to create a simplified botanical key to identify weedy amaranths; (ii) to determine the number and type of sites of action the accession are resistant to, i.e. resistance pattern; and (iii) to determine the main resistance mechanisms involved d) to evaluate the efficacy of herbicides with different site of action. RESULTS An easy‐to‐use botanical key was devised and successfully used in the infested sites and results were confirmed through a species‐specific molecular marker. Amaranthus retroflexus L. (redrood pigweed) was found in three sites; plants with Asp376Glu substitution at the ALS gene were resistant to thifensulfuron‐methyl. Amaranthus tuberculatus (Moq.) J.D.Sauer (waterhemp) and Amaranthus hybridus L. (smooth pigweed) accessions were cross‐resistant to thifensulfuron‐methyl and imazamox; most ALS‐resistant plants had a point mutation at position 574. One A. hybridus accession had the substitution Trp574Met, new for Amaranthus genus. All ALS‐resistant accessions were controlled by glyphosate and metribuzin. A. retroflexus accessions were controlled by bentazon, instead an A. hybridus and some A. tuberculatus accession were not. CONCLUSIONS The simplified botanical key proposed herein could be a useful tool for farmers and weed scientists to reliably identify Amaranthus species in the field. The main resistance mechanism in the three Amaranthus species is target‐site mediated. This is the first evidence of ALS‐resistant A. tuberculatus outside its native North American range. © 2019 Society of Chemical Industry

Population structure and evolution of resistance to acetolactate synthase (ALS)‐inhibitors in Amaranthus tuberculatus in Italy

“…Seven of eight A. tuberculatus populations used in this study were described in a previous paper 10 . The original population codes were simplified as follows: G, 10–10L; F, 10–13L; A, 14–35L; B, 17–56; D, 17–60; H, 17–61; E, 17–65.…”

“…Despite its invasiveness, weedy waterhemp in crop fields was discovered in the eastern Po Valley only in 2010. Since then, other field populations have been identified in the Emilia‐Romagna (2014) and Veneto (2017) regions 10 . All of these populations were cross‐resistant to thifensulfuron‐methyl and imazamox due to a substitution at codon 574 of the ALS gene that is known to cause broad cross‐resistance to ALS inhibitors in A. tuberculatus 10,11 .…”

Herbicide resistance in Amaranthus tuberculatus†

“…10 Although there are few reports of weedy populations of A. tuberculatus outside of the United States and Canada, herbicide-resistant populations infesting cultivated fields recently were reported in Italy. 11 Understanding the evolution of herbicide resistance in A. tuberculatus requires some knowledge of its biological characteristics. Rapid growth rate, high seed production, asynchronous seed germination, and dioecy are prominent biological characteristics contributing to its weediness.…”

“…Amaranthus tuberculatus continues to expand its range, now being found in Canada, and it has emigrated to western Asia and Europe 10 . Although there are few reports of weedy populations of A. tuberculatus outside of the United States and Canada, herbicide‐resistant populations infesting cultivated fields recently were reported in Italy 11 …”

Combination of Herbicide Band Application and Inter-Row Cultivation Provides Sustainable Weed Control in Maize

“…Band application can therefore be a feasible and sustainable approach to allow the use of active ingredients with non-optimal eco-toxicological characteristics, such as some pre-emergence herbicides commonly applied on maize. In recent years resistance to the main post-emergence herbicides used on maize, mainly ALS-inhibitors, was reported in Italy for troublesome summer weeds such as Echinochloa and Amaranthus species [30,31]; therefore retaining the availability of a wide range of active ingredients with different sites of action is crucial to manage the existing resistant populations and prevent further evolution and diffusion of herbicide resistance in maize fields.…”