ACCase inhibitor resistant wild oat in Manitoba : prediction, identification, and characterization

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Bourgeois, Luc.
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High use of aryloxyphenoxypropionate (APP) and cyclohexanedione (CHD), collectively referred to as acetyl coenzyme A carboxylase (ACCase) inhibiting or Group 1 herbicides, has led to the selection of resistant wild oat (Avena fatua) populations in some regions of Manitoba. The first objective of this thesis was to determine areas of Manitoba at low, medium, and high risk of developing Group 1 resistance. This objective was achieved by using data included in the Manitoba Crop Insurance Corporation (MCIC) database. Low, medium, and high risk areas were those in which Group 1 herbicides were sprayed on less than 30%, 30 to 50%, and over 50% of the sprayed fields, respectively. Results showed that Group 1 herbicide use increased from 15 to 50% of the sprayed fields between 1981 and 1993. Almost 40% of the townships were at high risk between 1989 and 1993. Wild oat seeds were collected in fields from different risk areas with the second objective of determining the proportion of fields infested with resistant wild oat. In a high risk township, resistant wild oat occurred in 20 out of 30 surveyed fields. In general, Group 1 resistant wild oat were more common in high risk townships than in medium or low risk townships. Finally, the third objective was to characterize resistant wild oat lines according to cross-resistance patterns and to determine which one, if any, is the most common. Cross-resistance levels were based on seed-bioassay, and more specifically on the coleoptile length. Three types of cross-resistance were established. The first type included wild oat lines with high levels of resistance to the APP and CHD chemical families. The second type included lines with low levels of resistance to both chemical families, while the third type included lines with high levels of resistance to APP's but almost no resistance to CHD's. More than one type was found in some fields which indicates independent selection of several mutants within a field. Overall wild oat types with high levels of resistance to both chemical families were the most common.