CHARACTERIZATION OF CROSS-RESISTANCE PATTERNS IN ACETYL-COA CARBOXYLASE INHIBITOR RESISTANT WILD OAT (AVENA-FATUA)

The purpose of this study was to determine cross-resistance patterns a mong wild oat lines resistant to acetyl-CoA carboxylase (ACCase) inhib itors and to determine which, if any, cross-resistant type was more co mmon than another Discriminatory concentrations of two aryloxyphenoxy- propionates (APP) and three cyclohexanediones (CHD) were determined us ing a petri-dish bioassay. These concentrations were then applied to 8 2 resistant wild oat lines identified in previous studies. In addition , two resistant standards (UM1 and UM33) and a susceptible standard (U M5) were included in the experiments. Coleoptile lengths expressed as percentages of untreated controls were used to assess the level of res istance to each herbicide. Large variations were observed among wild o at lines and herbicides. However, cluster analysis summarized the rela tionship between the five herbicides (variables) and the wild oat line s into three main cross-resistance types. Type A included wild oat lin es with high resistance to APP herbicides and no or low resistance to CHD herbicides. Types B and C included those with low to moderate resi stant and high levels of resistance to all five herbicides, respective ly. Type C was the most common cross-resistance type. Relationships am ong herbicides were determined using pairwise correlation and principa l component analysis (PCA). All correlations were high between APP her bicides and between CHD herbicides but not between APP and CHD herbici des. The first two axes of the PCA accounted for 88.4% of the total va riance, with the first axis correlated to the CHD herbicides and the s econd axis correlated to the APP herbicides. In the PCA, wild oat line s were segregated into the three types identified in the cluster analy sis. Although CHD and APP herbicides bind at the same region on the AC Case, resistant wild oat lines respond differently to them.