The ecological fitness of ALS‐resistant Amaranthus retroflexus and multiple‐resistant Amaranthus blitoides

Abstract

Field studies were conducted to evaluate the ecological fitness of Amaranthus spp. biotypes that evolved resistance to either acetolactate synthase (ALS) inhibitors (A. retroflexus, SuR), to triazine herbicides (A. blitoides, SuS ⁄ TR), or to both (A. blitoides, SuR ⁄ TR), and estimate their ecological fitness under competitive conditions. The plants were grown in monoculture and in replacement series experiments. The examined mixtures were 100%S, 75%S ⁄ 25%R, 50%S ⁄ 50%R, 25%S ⁄ 75%R and 100%R, at a constant stand of 400 plants m )2 . The SuR and SuS A. retroflexus biotypes attained similar shoot dry biomass per plant, biomass per plot and relative yield total (RYT) ¼ 1. In monoculture, the final shoot biomass of A. blitoides biotypes SuS ⁄ TS plants was higher than that of SuR ⁄ TR and SuS ⁄ TR. A negative effect of association was observed, amensalism, when SuS ⁄ TS was grown in mixture with SuR ⁄ TR, in favour of the wild type. However, SuR ⁄ TR and SuS ⁄ TR biomass was not influenced by the presence of the competitor. These data support the hypothesis that the ALS-resistance trait in A. retroflexus and A. blitoides is not associated with growth penalty and did not incur ecological cost in the field. We suggest that the cause of the observed reduction in growth rendering the SuS ⁄ TR and SuR ⁄ TR less fit than the wild type is due to the triazine resistance, and may facilitate their dissipation.

Nucleotide substitutions in the acetolactate synthase genes of sulfonylurea-resistant biotypes of Monochoria vaginalis (Pontederiaceae)

“…However, these 13 amino acids do not interact with pyruvate, the substrate of ALS (Pang et al, 2002). These data indicate that these amino acids do not play an important role in catalysis; this is consistent with other observations, such as that the mutations conferring resistance to ALS inhibitors do not affect enzymatic properties (Lee et al, 1999;Duggleby et al, 2003) and that the acquisition of ALS inhibitor resistance does not decrease the fitness of an individual (Thompson et al, 1994a;Thompson et al, 1994b;Christoffoleti et al, 1997;Sibony and Rubin, 2003a). Because of the lack of a fitness deficiency in ALS inhibitor-resistant biotypes under herbicide-free conditions, it is very difficult to completely eliminate the resistant biotypes from agricultural fields.…”

Valor adaptativo e habilidade competitiva de azevém resistente e suscetível ao iodosulfuron em competição com o trigo

“…Não foram relatadas diferenças na capacidade competitiva de biótipos resistentes aos inibidores da ALS, para várias espécies (Sibony & Rubin, 2003;Lamego et al, 2011;Légère et al, 2013). A falta de efeitos negativos em biótipos resistentes aos inibidores da enzima ALS favorece a evolução, a propagação e a competitividade dessas espécies nos sistemas agrícolas (Légère et al, 2013).…”

Competitiveness of ALS inhibitors resistant and susceptible biotypes of Greater Beggarticks (Bidens subalternans)

“…In which case, the resistant plants will be at a disadvantage once the herbicide selection pressure is removed. Sibony & Rubin (2003) showed that ALS-resistant and -susceptible biotypes of redroot pigweed (Amaranthus retroflexus) expressed similar ecological fitness. Also, studies on ALS-resistant Kochia scoparia, downy brome (Bromus tectorum), prostrate pigweed (Amaranthus blitoides), common cocklebur (Xanthium strumarium), common sunflower (Helianthus annuus), and prairie sunflower (Helianthus petiolaris) did not show growth penalty (Christoffoleti et al, 1997;Park et al, 2004;Crooks et al, 2005;Massinga et al, 2005).…”