Distinct non-target site mechanisms endow resistance to glyphosate, ACCase and ALS-inhibiting herbicides in multiple herbicide-resistant Lolium rigidum

Abstract

This study investigates mechanisms of multiple resistance to glyphosate, acetyl-coenzyme A carboxylase (ACCase) and acetolactate synthase (ALS)-inhibiting herbicides in two Lolium rigidum populations from Australia. When treated with glyphosate, susceptible (S) plants accumulated 4- to 6-fold more shikimic acid than resistant (R) plants. The resistant plants did not have the known glyphosate resistance endowing mutation of 5-enolpyruvylshikimate-3 phosphate synthase (EPSPS) at Pro-106, nor was there over-expression of EPSPS in either of the R populations. However, [(14)C]-glyphosate translocation experiments showed that the R plants in both populations have altered glyphosate translocation patterns compared to the S plants. The R plants showed much less glyphosate translocation to untreated young leaves, but more to the treated leaf tip, than did the S plants. Sequencing of the carboxyl transferase domain of the plastidic ACCase gene revealed no resistance endowing amino acid substitutions in the two R populations, and the ALS in vitro inhibition assay demonstrated herbicide-sensitive ALS in the ALS R population (WALR70). By using the cytochrome P450 inhibitor malathion and amitrole with ALS and ACCase herbicides, respectively, we showed that malathion reverses chlorsulfuron resistance and amitrole reverses diclofop resistance in the R population examined. Therefore, we conclude that multiple glyphosate, ACCase and ALS herbicide resistance in the two R populations is due to the presence of distinct non-target site based resistance mechanisms for each herbicide. Glyphosate resistance is due to reduced rates of glyphosate translocation, and resistance to ACCase and ALS herbicides is likely due to enhanced herbicide metabolism involving different cytochrome P450 enzymes.

Evaluation of the Mechanism Responsible for the Low-Level Resistance to Glyphosate in Goosegrass

“…ha -1 and without the addition of an adjuvant, malathion, an inhibitor of metabolism action at a dose of 1,000 g a.i. ha -1 , was applied (Yu et al, 2009). In both applications, a knapsack sprayer was used, pressurized at CO 2 , with AVI 110.015 fan-type spraying nozzle tips, which provided an application volume of 150 L ha -1 .…”

“…ha -1 (Vargas et al, 2013). Therefore, the hypothesis that the 6 one by reducing the translocation of the herbicide and, for the others, for differentiated metabolism action of the herbicide with the action of P450 complex (Yu et al, 2009). Also for Digitaria insularis, glyphosate was degraded into aminomethylphosphonic acid (AMPA), glyoxylate, and sarcosine in the resistant biotype, whereas the susceptible biotype showed little glyphosate degradation potential, and this mechanism may contribute to the species resistance (Carvalho et al, 2012).…”

“…The inhibition of cyt-P450 complex by applying malathion and amitrole has shown multiple resistance to chlorsulfuron and diclofop, respectively, in a biotype of Lolium rigidum related to metabolizing herbicides (Yu et al, 2009). Inhibitor 1-aminobenzotriazole has also indicated the metabolism of herbicide chlortuluron via cyt-P450, providing the resistance of Bromus tectorum to the herbicide (Menendez et al, 2006).…”

“…The resistance mechanisms may result from changes in the herbicide target sites (target site resistance), as in the case of populations of Eleusine indica resisting to glyphosate due to the replacement of amino acids in positions 102 and 106 of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) (Yu et al, 2015) or by changes that do not occur in the site of action (non-target site resistance) (Powles and Yu, 2010). This latter resistance mechanism may involve the reduction of the uptake and translocation of the herbicide, as for Conyza bonariensis (Dinelli et al, 2008) resisting to glyphosate, compartmentalization of glyphosate in the vacuole in C. canadensis (Ge et al, 2009) or even the metabolism action such as resistance of Lolium rigidum to acetolactate synthase (ALS) and ACCase inhibitors (Yu et al, 2009). …”

Verification of the Mechanism of Glyphosate Resistance in Italian Ryegrass Biotypes

“…The previous application of metabolism inhibitors may partially or completely reduce the expression of detoxifying enzymes, thus, reducing the resistance factor of the biotypes (Matzenbacher, 2012). The inhibition of the cyt-P450 complex by applying malathion and amitrol showed the multiple resistance to chlorsulfuron and diclofop, respectively, on a Lolium rigidum biotype, related to the metabolism of these herbicides (Yu et al, 2009). …”