Glyphosate-resistant smooth-pigweed (Amaranthus hybridus) in Brazil

Abstract

Background: Amaranthus hybridus, a common agricultural weed in Brazil, has been associated with complications in the management of major crops. Recently, A. hybridus biotypes with suspected resistance to the herbicide glyphosate have been observed in the state of Paraná. Objective: To characterize glyphosate-resistant Amaranthus hybridus biotypes. Methods: Three independent experiments were conducted to evaluate four biotypes of A. hybridus. Twelve doses of glyphosate were applied, including 64D, 32D, 16D, 8D, 4D, 2D, D, 1/2D, 1/4D, 1/8D, 1/16D, and a control with no herbicide. The dose D of glyphosate applied was 1080 g ha -1 ae. Four replicates for each treatment and a randomized block design were used. At 28 (DAA), the control (%) and residual dry mass of each plot were analyzed. Results: The biotypes with suspected resistance (R1, R2, and R3) had a GR 50 in the range of 3019.13 to 3316.45 g ha -1 ae and LD 50 in the range of 4081.52 to 4310.29 g ha -1 ae whereas the susceptible biotype had a GR 50 of 227.63 g ha -1 ae and LD 50 of 196.59 g ha -1 ae. Conclusions: Biotypes R1, R2, and R3 are resistant to the herbicide glyphosate.

Spodoptera eridania (Lepidoptera: Noctuidae): first report on Amaranthus hybridus (Amaranthaceae) in Brazil

“…The genus Amaranthus has a great importance in agriculture as it includes a lot of species considered as weeds. It has been reported in recent studies difficulty in controlling A. hybridus due the resistance to glyphosate, the main herbicide used for its control (García et al, 2020;Resende et al, 2022). Besides that, these plants can remain in crops becoming a green bridge for herbivorous insects that damage crops of interest reducing producer profit (Moraes et al, 2020).…”

Use of vegetation cover in the control of different species of the genus Amaranthus

“…Among the practices employed in weed management, the intensive use of an herbicide or herbicides with the same mechanism of action has been selecting tolerant species and resistant biotypes of weeds in the field (CHRISTOFFOLETI et al, 1994;JALALUDIN et al, 2014). Species of the genus Amaranthus stand out among the weeds selected by this management practice due to their high production and seed dispersal, long seed longevity, genetic variability, and high growth rate, which give these species a high ability to adapt to different environmental conditions and develop resistance to herbicides, making this weed difficult to control (CRUZ et al, 2020;HEAP, 2021;RESENDE et al, 2021).…”

“…Dentre as práticas empregadas no manejo de plantas daninhas, o uso intensivo de um herbicida ou herbicidas com o mesmo mecanismo de ação vem selecionando no campo espécies tolerantes e biótipos resistentes de plantas daninhas (CHRISTOFFOLETI et al, 1994;JALALUDIN et al, 2014). Entre as plantas daninhas selecionadas por essa pratica de manejo, as espécies do gênero Amaranthus se destacam em razão da alta produção e dispersão de sementes, ampla longevidade de sementes, variabilidade genética e alta taxa de crescimento, que conferem a essas espécies grande capacidade de se adaptar a diferentes condições de ambientes e desenvolver resistência aos herbicidas, tornando essa planta daninha de difícil controle (CRUZ et al, 2020;HEAP, 2021;RESENDE et al, 2021).…”

Smooth pigweed (Amaranthus hybridus) and unresolved Amaranthus spp. from Brazil resistant to glyphosate exhibit the EPSPS TAP-IVS substitution

“…It can reduce soybean grain yield by 82%, and the presence of one A. hybridus plant per square meter can result in a 6.4% yield reduction (Soltani et al 2017; Zandoná et al 2022). The importance of this species is increasing, including in Brazil, as resistance cases are reported (García et al 2020; Perotti et al 2019; Resende et al 2020; Whaley et al 2006).…”

“…Currently, A. hybridus populations have been identified with resistance to inhibitors of photosystem II, acetolactate synthase (ALS), protoporphyrinogen oxidase, 5-enol-pyruvylshikimate-3-phosphate synthase (EPSPS), and to the synthetic auxin herbicides (Heap 2023). Amaranthus hybridus biotypes from Brazil were identified with resistance to the EPSPS inhibitor, glyphosate, and to ALS-inhibiting herbicides (Mendes et al 2022; Resende et al 2020). However, the mechanism of resistance to ALS-inhibiting herbicides in biotypes from Brazil has not been characterized.…”