Glyphosate-Resistant Parthenium hysterophorus in the Caribbean Islands: Non Target Site Resistance and Target Site Resistance in Relation to Resistance Levels

Abstract

Glyphosate has been the most intensely herbicide used worldwide for decades, and continues to be a single tool for controlling weeds in woody crops. However, the adoption of this herbicide in a wide range of culture systems has led to the emergence of resistant weeds. Glyphosate has been widely used primarily on citrus in the Caribbean area, but a study of resistance in the Caribbean islands of Cuba and the Dominican Republic has never been carried out. Unfortunately, Parthenium hysterophorus has developed glyphosate-resistance in both islands, independently. The resistance level and mechanisms of different P. hysterophorus accessions (three collected in Cuba (Cu-R) and four collected in the Dominican Republic (Do-R) have been studied under greenhouse and laboratory conditions. In in vivo assays (glyphosate dose causing 50% reduction in above-ground vegetative biomass and survival), the resistance factor levels showed susceptible accessions (Cu-S ≥ Do-S), low-resistance accessions (Cu-R3 < Do-R4), medium-resistance accessions (Do-R3 < Cu-R2 < Do-R2) and high-resistance accessions (Do-R1 < Cu-R1). In addition, the resistance factor levels were similar to those found in the shikimic acid accumulation at 1000 μM of glyphosate (Cu-R1 ≥ Do-R1 > Do-R2 > Cu-R2 > Do-R3 > Do-R4 > Cu-R3 >> Cu-S ≥ Do-S). Glyphosate was degraded to aminomethylphosphonic acid, glyoxylate and sarcosine by >88% in resistant accessions except in Cu-R3 and Do-R4 resistant accessions (51.12 and 44.21, respectively), whereas a little glyphosate (<9.32%) was degraded in both susceptible accessions at 96 h after treatment. There were significant differences between P. hysterophorus accessions in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity enzyme with and without different glyphosate rates. The R accessions showed values of between 0.026 and 0.21 μmol μg−1 TSP protein min−1 basal EPSPS activity values with respect to the S (0.024 and 0.025) accessions. The same trend was found in the EPSPS enzyme activity treated with glyphosate, where a higher enzyme activity inhibition (glyphosate μM) corresponded to greater resistance levels in P. hysterophorus accessions. One amino acid substitution was found at position 106 in EPSPS, consisting of a proline to serine change in Cu-R1, Do-R1 Do-R2. The above-mentioned results indicate that high resistance values are determined by the number of defense mechanisms (target-site and non-target-site resistance) possessed by the different P. hysterophorus accessions, concurrently.

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

“…Control levels attained for the several S populations tested for each Conyza species clearly showed that glyphosate is still a useful herbicide when used as part of an IWM scheme. Control failures are often due to applications at too advanced growth stages or to ignoring environmental factors during herbicide use . Such situations could lead to possible resistance in a few years.…”

“…In fact, this situation is becoming more common because of selection pressure. However, there are no reports about which mechanism develops first, or how each mechanism individually contributes to the resistance levels exhibited …”

“…However, there are no reports about which mechanism develops first, or how each mechanism individually contributes to the resistance levels exhibited. 16,17 The main objectives of this study were to: (a) elucidate the taxonomical identity of putative resistant populations of Conyza spp. based on molecular analysis; (b) evaluate their resistance levels and the mechanisms involved; and (c) test chemical alternatives for control of the resistant populations.…”

Evidence, Mechanism and Alternative Chemical Seedbank-Level Control of Glyphosate Resistance of a Rigid Ryegrass (Lolium rigidum) Biotype from Southern Spain

“…This result is consistent with previous studies in other glyphosate-resistant rigid ryegrass populations that did not demonstrate any contribution of metabolism to resistance (Fernandez et al, 2015). In fact, glyphosate metabolism does not seem to be a frequent resistance mechanism (Duke, 2011) and, to date, only sourgrass (de Carvalho et al, 2012), horseweed (Gonzalez-Torralva et al, 2012), and ragweed parthenium (Bracamonte et al, 2016) have been described as species able to transform glyphosate into non-toxic compounds.…”

“…Thus, it is plausible to assume that reduced uptake and translocation are the primary causal mechanisms of glyphosate resistance in the studied RG biotype of rigid ryegrass. Lower glyphosate uptake in the RG compared to SG biotype could be explained by structural differences in outer leaf surfaces (Shepherd and Griffiths, 2006; Rojano-Delgado et al, 2012; Alcántara-de la Cruz et al, 2016a), while reduced translocation could result from increased retention of glyphosate in the tips of treated leaves (de Carvalho et al, 2012; Gonzalez-Torralva et al, 2012, 2014; Adu-Yeboah et al, 2014; Bracamonte et al, 2016). …”