A nonnative Palmer amaranth (Amaranthus palmeri) population in the Republic of South Africa is resistant to herbicides with different sites of action

Abstract

Palmer amaranth (Amaranthus palmeri S. Watson) is not native to Africa. Based on the presence and persistence of A. palmeri populations, its invasive status in southern Africa is classified as “naturalized”. Globally, A. palmeri is one of the most troublesome weed species in several crops including soybean [Glycine max (L.) Merr.], maize (Zea mays L.), and cotton (Gossypium hirsutum L.). Certain populations of A. palmeri in various countries were reported to be resistant to herbicides with different sites-of-action (SOAs). Two biotypes of A. palmeri in the United States of America reportedly each have resistance to herbicides representing five different SOAs, and between them a total of eight different SOAs are involved. Resistance mechanisms in these biotypes involve target site and/or non-target site resistance. Here we characterize a specific A. palmeri population that was found in Douglas district in South Africa and showed resistance to various herbicide SOAs. Initially, this A. palmeri population was discovered in a glyphosate-tolerant cotton field, where it survived glyphosate treatment. Subsequently, greenhouse experiments were conducted to characterize this A. palmeri population for potential resistance to herbicides of additional SOAs, and molecular analyses were conducted to reveal the mechanisms of herbicide resistance. Results indicated resistance to chlorimuron ethyl and glyphosate in this population, while <90% control (decreased sensitivity) was observed at the label rate for mesotrione, atrazine, saflufenacil, and s-metolachlor. However, glufosinate, tembotrione, acifluorfen, dicamba, 2,4-D, metribuzin, acetochlor, isoxaflutole, diflufenican and pyroxasulfone were effective at controlling this population. This profiling of herbicide sensitivity has allowed development of programs to control and potentially minimize the spread of this weed. In addition, molecular analysis of EPSPS revealed the role of higher copy number as a mechanism for glyphosate resistance in this population, and a Ser-653-Asn target site mutation likely conferring resistance to the ALS-inhibitor chlorimuron-ethyl. No known target site mutations were identified for the PPO-inhibitor group.

Occurrence ofAmaranthus palmeriin Israeli agriculture: status of spread and response to glyphosate and trifloxysulfuron

“…DNA extraction was performed using the same procedures as described in Matzrafi et al (2017). Primers that were used to sequence the ALS gene and the PCR procedure are described in Reinhardt et al (2022). Sequence analyses and alignment were performed using the BioEdit software (Hall, 1999).…”

“…The nucleotide sequence of the ALS gene was amplified using two pairs of primers (Reinhardt et al, 2022). Sequences were then aligned with each other and compared to the A. thaliana ALS gene, in order to identify the nucleotide substitutions leading to point mutations.…”

Confirmation of a four-way herbicide-resistant Palmer amaranth (Amaranthus palmeri) population in Iowa

“…Previous research reported that newly introduced A. palmeri populations in the United States, Brazil, Turkey, and South Africa were confirmed to be MHR (Faleco et al 2022;Küpper et al 2017;Mennan et al 2021;Reinhardt et al 2022). Wisconsin researchers reported a recently discovered A. palmeri population was threeway MHR and survived labeled rates of imazethapyr, glyphosate, and atrazine (Faleco et al 2022).…”

Metabolism of the 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor, Mesotrione, in Multiple-Herbicide-Resistant Palmer amaranth (Amaranthus palmeri)

“…10 Seasonal and long-term control of Palmer amaranth is difficult because it has a season-long emergence pattern, vigorous seedling growth, the ability to rapidly replenish the soil seed bank, and a tendency to evolve resistance to herbicides. 9,11,12 From its native origins in the Sonoran Desert, Palmer amaranth populations have spread throughout different areas of the United States, 13 parts of South America, 6 and recently in South Africa, 14 including multiple-herbicide-resistant (MHR) populations, 14 either due to trade of contaminated farm equipment, crop seeds, or other raw food materials. To date, Palmer amaranth has evolved resistance to nine herbicide sitesof-action, including the 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides, and numerous MHR Palmer amaranth populations have contributed to its success as an invasive weed.…”