Non-target Site Tolerance Mechanisms Describe Tolerance to Glyphosate in Avena sterilis

Abstract

Sterile wild oat (Avena sterilis L.) is an autogamous grass established in warm climate regions. This species has been used as a cover crop in Mediterranean perennial crops during the spring period prior to initiating competition with the main crop for water and nutrients. However, such cover crops need to be controlled (by glyphosate or tillage) before the beginning of summer period (due to the possibility of intense drought stress). In 2011, the olive grove farmers of southern Spain expressed dissatisfaction because of the ineffective control with glyphosate on A. sterilis. Experiments were conducted to determine whether the continued use of glyphosate over a 5 year period had selected a new resistant or tolerant species. The GR50 values obtained for A. sterilis were 297.12 and 245.23 g ae ha−1 for exposed (E) and un-exposed (UE) glyphosate accessions, respectively. The spray retention and shikimic acid accumulation exhibited a non-significant difference between the two accessions. The results of 14C- glyphosate absorption was the same in the two accessions (E and UE), while the translocation from the treated leaf to the rest of the shoots and roots was similar in A. sterilis accessions. Glyphosate metabolism to aminomethylphosphonic acid (AMPA) and glyoxylate was similar in both accessions, but increased after treatment with glyphosate, indicating that metabolism plays an important role in tolerance. Both A. sterilis accessions, present similarity in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity enzyme with different glyphosate concentrations and without glyphosate, confirming that both accessions present the same genomic characteristics. The above-mentioned results indicate that innate tolerance to glyphosate in A. sterilis is probably and partly due to reduced herbicide absorption and translocation and metabolism compared to the susceptibility of other grasses weeds like Chloris inflata, Eleusine indica, and Lolium rigidum.

Mechanisms of glyphosate resistance and response to alternative herbicide‐based management in populations of the three Conyza species introduced in southern Spain

“…Although metabolism assays are carried out in many studies determining resistance, this mechanism appears to be of low importance in glyphosate‐resistant weeds. However, in innate glyphosate‐tolerant weeds its importance as a responsible mechanism increases …”

First Resistance Mechanisms Characterization in Glyphosate-Resistant Leptochloa virgata

“…In addition, L. virgata was effectively controlled previously with glyphosate (Pérez-López et al, 2014; Alcántara-de la Cruz et al, 2016c). According to bibliography, innate tolerance to glyphosate not involve target site tolerance mechanisms within the same species, and the tolerant populations generally are compared with sensitive populations of other species (Yuan et al, 2002; Alcántara-de la Cruz et al, 2016a; Fernández-Moreno et al, 2016; Mao et al, 2016). To demonstrate the innate glyphosate tolerance in species such as: Avena sterilis, Cologania broussonetii, Dicliptera chinensis, Liriope platyphylla, Liriope spicata, Ophiopogon japonicas , among others, it has been necessary compare them with glyphosate sensitive species.…”

Trp‐1999‐Ser mutation of acetyl‐CoA carboxylase and cytochrome P450s‐involved metabolism confer resistance to fenoxaprop‐P‐ethyl in Polypogon fugax

“…), water chickweed ( Myosoton aquaticum L.), rigid brome ( Bromus rigidus Roth. ), and wild oat species ( Avena fatua L. and Avena sterilis L.) . Several candidate genes putatively associated with NTSR were also identified in different species.…”

“…), 17 and wild oat species (Avena fatua L. and Avena sterilis L.). 18,19 Several candidate genes putatively associated with NTSR were also identified in different species. Asia minor bluegrass (Polypogon fugax Nees ex Steud.)…”