First Resistance Mechanisms Characterization in Glyphosate-Resistant Leptochloa virgata.

José A Domínguez-Valenzuela,Francisco Barro,Rafael De Prado,María J Giménez,Hugo E Cruz-Hipolito,Ricardo Alcántara-De La Cruz,Antonia M Rojano-Delgado

doi:10.3389/fpls.2016.01742

Abstract

Leptochloa virgata (L.) P. Beauv. is an annual weed common in citrus groves in the states of Puebla and Veracruz, Mexico limiting their production. Since 2010, several L. virgata populations were identified as being resistant to glyphosate, but studies of their resistance mechanisms developed by this species have been conducted. In this work, three glyphosate-resistant populations (R8, R14, and R15) collected in citrus orchards from Mexico, were used to study their resistance mechanisms comparing them to one susceptible population (S). Dose-response and shikimic acid accumulation assays confirmed the glyphosate resistance of the three resistant populations. Higher doses of up to 720 g ae ha-1 (field dose) were needed to control by 50% plants of resistant populations. The S population absorbed between 7 and 13% more 14C-glyphosate than resistant ones, and translocated up to 32.2% of 14C-glyphosate to the roots at 96 h after treatment (HAT). The R8, R14, and R15 populations translocated only 24.5, 26.5, and 21.9%, respectively. The enzyme activity of 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS) was not different in the S, R8 and R14 populations. The R15 Population exhibited 165.9 times greater EPSPS activity. Additionally, this population showed a higher EPSPS basal activity and a substitution in the codon 106 from Proline to Serine in the EPSPS protein sequence. EPSPS gene expression in the R15 population was similar to that of S population. In conclusion, the three resistant L. virgata populations show reduced absorption and translocation of 14C-glyphosate. Moreover, a mutation and an enhanced EPSPS basal activity at target-site level confers higher resistance to glyphosate. These results describe for the first time the glyphosate resistance mechanisms developed by resistant L. virgata populations of citrus orchards from Mexico.

Highlights

Glyphosate is the most extensively used systemic foliar herbicide of broad spectrum used for over 40 years to control of annual and perennial weeds (Gomes et al, 2014; Armendáriz et al, 2016)
Glyphosate resistance was confirmed in the three L. virgata populations (R8, R14, and R15) collected in Persian lime groves from Veracruz
A field dose of glyphosate (720 g ae ha−1), used in Persian lime groves of Veracruz, was enough to achieve full control in the S population. With this dose of glyphosate, only 50% mortality was observed in R8 and R14 populations, and to the R15 for population, a dose 1.8 times more glyphosate than the field dose was required to obtain the same level of control

Summary

Introduction

Glyphosate is the most extensively used systemic foliar herbicide of broad spectrum used for over 40 years (early 1970s) to control of annual and perennial weeds (Gomes et al, 2014; Armendáriz et al, 2016). Resistance to glyphosate could be caused by different mechanisms either in the target or non-target site (Salas et al, 2015). Both groups limiting the amount of glyphosate which reaches the EPSPS at toxic levels, or causing a loss of affinity between the EPSPS and the glyphosate (Powles, 2010). Glyphosate is the only herbicide known to evolve amplification of the target-site (EPSPS) conferring resistance with field applications (Ribeiro et al, 2014)

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