Resistance to Glyphosate in Junglerice (Echinochloa colona) from California

Abstract

A suspected glyphosate-resistant (R) junglerice population was collected from a glyphosate-R corn field near Durham in northern California where glyphosate had been applied at least twice a year for over 6 yr. Based on the amount of glyphosate required to reduce growth by 50% (ED50), the R population was 6.6 times more R than the susceptible (S) standard population. Based on the glyphosate concentration that inhibits EPSPS by 50% based on shikimate accumulation (I50) in leaf discs, R plants were four times more R than S plants. By 3 d after treatment with 0.42 kg ae ha−1glyphosate, the S population had accumulated approximately five times more shikimate than the R population. No differences in [14C]-glyphosate uptake and translocation were detected between R and S plants. However, partial sequencing of theEPSPSgene revealed a mutation in R plants causing a proline to serine change at EPSPS position 106 (P106S). Our results reveal the first case of a P106S target site mutation associated with glyphosate resistance in junglerice.

Verification of the Mechanism of Glyphosate Resistance in Italian Ryegrass Biotypes

“…An analysis of regression was conducted, adjusting the data to the sigmoidal regression equations, according to Alarcón-Reverte et al (2013):…”

“…On a study with biotypes of Eleusine indica resistant to glyphosate in the state of Mississippi, shikimate accumulation values up to 800% higher than the ones of the susceptible biotype were observed (Molin et al, 2013). The differential response to glyphosate observed between the biotypes refers to a resistance mechanism or mechanisms that mitigate the toxic effects resulting from the mechanism of action of glyphosate on plants ( Alarcón-Reverte et al, 2013), and they may or may not be a result of the change on the site of action of the herbicide (Powles and Preston, 2006;Powles and Yu, 2010). The resistance mechanism due to the changed site of action may occur due to the exchange of one or more amino acids on the target enzyme, which hinders the correct coupling of the herbicide, or even due to the overexpression of the target enzyme (Powles and Yu, 2010).…”

“…When related to the site of action, resistance may be a result of the reduced affinity of the herbicide for the site of action (enzyme), as a result of DNA mutation, or due to the overexpression of this enzyme. Different EPSPs gene mutations have been reported for conferring resistance to glyphosate on Lolium rigidum (Kaundun et al, 2011), Lolium multiflorum (Perez-Jones et al, 2005) and Echinochloa colona (Alarcón-Reverte et al, 2013). When the resistance is not related to the site of action, it may occur due to mechanisms such as reduced absorption, reduced or increased translocation and increased metabolism and compartmentalization (Powles and Yu, 2010).…”

Herbicide-resistant weeds challenge some signature cropping systems

“…Junglerice (Echinochloa colona) resistant to glyphosate was first identified in 2008 in a Roundup Ready corn field in the Sacramento Valley (Alarcon-Reverte et al 2013); since then, glyphosate-resistant junglerice has become widespread in orchards and field crops throughout California (Moretti, Garcia et al 2013). Resistance appears to be due to mutations in the EPSPS target site (Alarcon-Reverte et al 2013), although some populations also appear to have enhanced EPSPS activity (A.J.…”

“…Resistance appears to be due to mutations in the EPSPS target site (Alarcon-Reverte et al 2013), although some populations also appear to have enhanced EPSPS activity (A.J. Fischer, unpublished data).…”