First confirmation and characterization of target and non-target site resistance to glyphosate in Palmer amaranth ( Amaranthus palmeri ) from Mexico

Abstract

Following the introduction of glyphosate-resistant (GR)-cotton crops in Mexico, farmers have relied upon glyphosate as being the only herbicide for in-season weed control. Continuous use of glyphosate within the same year and over multiple successive years has resulted in the selection of glyphosate resistance in Palmer amaranth (Amarantus palmeri). Dose-response assays confirmed resistance in seven different accessions. The resistance ratio based on GR values (50% growth reduction) varied between 12 and 83. At 1000 μM glyphosate, shikimic acid accumulation in the S-accession was 30- to 2-fold higher at compared to R-accessions. At 96 h after treatment, 35-44% and 61% of applied C-glyphosate was taken up by leaves of plants from R- and S-accessions, respectively. At this time, a significantly higher proportion of the glyphosate absorbed remained in the treated leaf of R-plants (55-69%) compared to S-plants (36%). Glyphosate metabolism was low and did not differ between resistant and susceptible plants. Glyphosate was differentially metabolized to AMPA and glyoxylate in plants of R- and S-accessions, although it was low in both accessions (<10%). There were differences in 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) enzyme activity by 50% (I) between R- and S-accessions. However, no significant differences were found in the basal EPSPS activity (μmol inorganic phosphate μg total soluble protein min) between R- and S-accessions. A point mutation Pro-106-Ser was evidenced in three accessions. The results confirmed the resistance of Palmer amaranth accessions to glyphosate collected from GR-cotton crops from Mexico. This is the first study demonstrating glyphosate-resistance in Palmer amaranth from Mexico.

Distribution of glyphosate‐resistant Amaranthus spp. in Nebraska

“…The multiple glyphosate resistance mechanisms reported in common waterhemp, such as EPSPS target site mutation (Pro106Ser) and non‐target‐site resistance mechanisms with reduced glyphosate uptake and translocation, could contribute to the higher frequency of glyphosate resistance in common waterhemp when compared with Palmer amaranth. Although both glyphosate resistance mechanisms were also reported in a Palmer amaranth population from Mexico, the literature suggests that both mechanisms are more frequent in common waterhemp.…”

“…29 Glyphosate resistance mechanisms reported in common waterhemp populations include EPSPS gene amplification, 25,[39][40][41] EPSPS target site mutation, 24,25,33 and non-target-site resistance mechanisms with reduced glyphosate uptake and translocation. 42 EPSPS target site mutation and non-target-site resistance mechanisms with reduced glyphosate uptake and translocation were also reported in Palmer amaranth, 43 albeit at a lower frequency when compared with common waterhemp. According to Sammons and Gaines, accumulation of multiple resistance mechanisms under glyphosate selection pressure, especially in cross-pollinated species, leads to enhanced glyphosate resistance levels.…”

“…Agronomic variables, estimation of GR 50 and GR 90 , and resistance levels for selected common waterhemp populations from Nebraska. Resistance levels were calculated as the ratio of the GR 90 of each population to the glyphosate recommended label rate (868 g ae ha -1 ) amaranth population from Mexico, 43 the literature suggests that both mechanisms are more frequent in common waterhemp. The majority of the GR common waterhemp populations were collected in eastern Nebraska, where approximately 85% of these were collected in soybean fields.…”

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

“…TSR mechanisms involve one or more mutations in the DNA encoding the target protein of the herbicide, which leads to changes in amino acids or conformational changes in protein folding . Amplified basal expression of EPSPS for instance, also a TSR mechanism, provides additional active sites for phosphoenolpyruvate and S3P to bind normally and continue to move carbon flux through the shikimate pathway …”

“…13 Amplified basal expression of EPSPS for instance, also a TSR mechanism, provides additional active sites for phosphoenolpyruvate and S3P to bind normally and continue to move carbon flux through the shikimate pathway. 14 Each mechanism can show different levels of resistance. For example, in TSR, a single mutation in the EPSPS gene, Pro106 is the most common, confers low levels of resistance, in the order of 2-4-fold.…”