Characterization of cross-resistance patterns in acetyl-CoA carboxylase inhibitor resistant wild oat (Avena fatua)

Abstract

The purpose of this study was to determine cross-resistance patterns among wild oat lines resistant to acetyl-CoA carboxylase (ACCase) inhibitors and to determine which, if any, cross-resistant type was more common than another. Discriminatory concentrations of two aryloxyphenoxy-propionates (APP) and three cyclohexanediones (CHD) were determined using a petri-dish bioassay. These concentrations were then applied to 82 resistant wild oat lines identified in previous studies. In addition, two resistant standards (UM1 and UM33) and a susceptible standard (UM5) were included in the experiments. Coleoptile lengths expressed as percentages of untreated controls were used to assess the level of resistance to each herbicide. Large variations were observed among wild oat lines and herbicides. However, cluster analysis summarized the relationship between the five herbicides (variables) and the wild oat lines into three main cross-resistance types. Type A included wild oat lines with high resistance to APP herbicides and no or low resistance to CHD herbicides. Types B and C included those with low to moderate resistant and high levels of resistance to all five herbicides, respectively. Type C was the most common cross-resistance type. Relationships among herbicides were determined using pairwise correlation and principal component analysis (PCA). All correlations were high between APP herbicides and between CHD herbicides but not between APP and CHD herbicides. The first two axes of the PCA accounted for 88.4% of the total variance, with the first axis correlated to the CHD herbicides and the second axis correlated to the APP herbicides. In the PCA, wild oat lines were segregated into the three types identified in the cluster analysis. Although CHD and APP herbicides bind at the same region on the ACCase, resistant wild oat lines respond differently to them.

Cross Resistance of Acetyl-coa Carboxylase (ACCase) Inhibitor–Resistant Wild Oat (Avena fatua) Biotypes in the Pacific Northwest

“…Cross-resistance patterns were characterized using 82 ACCase inhibitor-resistant wild oat lines, in which lines were categorized into three resistant types, A, B, or C, based on cluster analysis (Bourgeois et al 1997). Type A was highly resistant to APP herbicides and had no or low resistance to CHD herbicides.…”

“…Types B and C were low to moderately resistant (type B) and highly (type C) resistant to both APP and CHD herbicides, respectively. In their (Bourgeois et al 1997) study, type C was the most common cross-resistance Table 3. Herbicides and rates used in dose-response studies with five resistant (R1 to R5) and susceptible (S) wild oat biotypes.…”

Resistance to acetyl‐CoA carboxylase‐inhibiting herbicides

“…However, these methods have rarely been used outside research owing to the high costs involved, restrictions to target‐site resistance only and ambiguity arising from multiple amino acid changes at specific resistance codon positions . Equally, methods based on pollen, seeds, enzyme and metabolism assays have not been widely adopted because they do not cover all possible resistance mechanisms and are therefore prone to false negative prediction of resistance. To date, the classical whole‐plant test using seeds collected at the end of the growing season remains the most commonly employed method for confirming resistance to ACCase herbicides .…”

Resistance to herbicides inhibiting the biosynthesis of very‐long‐chain fatty acids

“…A. fatua is highly prone to evolving resistance, and indeed single‐resistant and multiple‐resistant populations have been found across western Canada. A. fatua has been reported to be resistant to group A, group B, group K 2 and N. However, after 15–20 years, resistance to triallate (N) in A. fatua has not expanded much and appears to remain at low levels (<10%) in Canada, probably because the pre‐emergence herbicide is not commonly used now. Glasshouse studies have shown that A. fatua populations are up to tenfold more resistant than susceptible lines .…”