Occurrence of a herbicide-resistant acetyl-coenzyme A carboxylase mutant in annual ryegrass (Lolium rigidum) selected by sethoxydim

Abstract

Abstract. The spectrum of herbicide resistance was determined in an annual ryegrass (Lolium rigidum Gaud.) biotype (SLR 3) that had been exposed to the grass herbicide sethoxydim, an inhibitor of the plastidic enzyme acetylcoenzyme A carboxylase (ACCase, EC 6.4.1.2), for three consecutive years. This biotype has an 18-fold resistance to sethoxydim and enhanced resistance to other cyclohexanedione herbicides compared with a susceptible biotype (VLR 1). The resistant biotype also has a 47-to > 300-fold cross-resistance to the aryloxyphenoxypropanoate herbicides which share ACCase as a target site. No resistance is evident to herbicide with a target site different from ACCase. The absorption of [4-14C]sethoxydim, the rate of metabolic degradation and the nature of the herbicide metabolites are similar in the resistant and susceptible biotypes. While the total activity of the herbicide target enzyme ACCase is similar in extracts from the two biotypes, the kinetics of herbicide inhibition differ. The concentrations of sethoxydim and tralkoxydim required to inhibit the activity of ACCase by 50% are 7.8 and > 9.5 times higher, respectively, in the resistant biotype. The activity of ACCase from the resistant biotype was also less sensitive to aryloxyphenoxypropanode herbicides than the susceptible biotype. The spectrum of resistance at the whole-plant level is correlated with resistance at the ACCase level and confirms that a less sensitive form of the target enzyme endows resistance in biotype SLR 3.

High survival frequencies at low herbicide use rates in populations of Lolium rigidum result in rapid evolution of herbicide resistance

“…The pellet was resuspended in 2.5 ml elution buffer (50 mM Tricine, pH 8.0, 2.5 mM MgCl 2 , 50 mM KCl, 1 mM DTT) and desalted on a Sephadex G-25 (Pharmacia PD-10) column pre-equilibrated with elution buffer. The eluent was stored at À201C until use (modified from Tardif et al, 1993).…”

Resistance cost of a cytochrome P450 herbicide metabolism mechanism but not an ACCase target site mutation in a multiple resistant Lolium rigidum population

“…Individual L. rigidum plants can display multiple resistance to ACCase and ALS inhibiting herbicides owing to both target site-and nontarget site-based resistance mechanisms (Tardif et al ., 1993;Tardif & Powles, 1994;Preston et al ., 1996;Preston & Mallory-Smith, 2001). This phenomenon of multiple resistance provides an excellent opportunity to compare resistance costs associated with different herbicide resistance mechanisms in individuals within a single resistant population (similar genetic background).…”

Evolution of herbicide resistance in weeds: initial frequency of target site-based resistance to acetolactate synthase-inhibiting herbicides in Lolium rigidum

“…One unusual aspect of herbicide resistance in southern Australia has been the rapid evolution of resistance. Resistance to both ACCase-and ALSinhibiting herbicides has occurred with as few as three applications of these herbicides (Tardif et al, 1993;Powles et al, 1997;Preston et al, 1999). Gill (1995) established that of the L. rigidum populations sent for testing for herbicide resistance, all receiving four or more applications of ALSinhibiting herbicides, were resistant to these herbicides.…”