Factors affecting common lambsquarters' tolerance to imazethapyr
Ohki, Tooru
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Permalink
https://hdl.handle.net/2142/22479
Description
Title
Factors affecting common lambsquarters' tolerance to imazethapyr
Author(s)
Ohki, Tooru
Issue Date
1996
Doctoral Committee Chair(s)
Stoller, Edward W.
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Agriculture, Plant Pathology
Biology, Plant Physiology
Language
eng
Abstract
Field, greenhouse, and laboratory experiments were conducted to examine the tolerance mechanisms of common lambsquarters (Chenopodium album) to imazethapyr (2- (4,5-dihydro-4-methyl-(1-methylethyl)-5-oxo-1H-imidazol-2-yl) -5-ethyl-3-pyridinecarboxylic acid, active ingredient of Pursuit$\sp\circler$ herbicide) by comparing it with susceptible smooth pigweed (Amaranthus hybridus). Both field and greenhouse studies, conducted in Illinois in 1994, showed common lambsquarters to be more tolerant than smooth pigweed, especially at the late growth stages. To determine mechanisms involved in tolerance, imazethapyr absorption, translocation, and metabolism were investigated. Decreased absorption rate of imazethapyr was observed in both species at late growth stage and these factors may account for reduced efficacy of the herbicide at later growth stages. Effective control of common lambsquarters at an early growth stage could be attributed to rapid accumulation of imazethapyr in plant parts above the treated leaf. However, reduced efficacy of imazethapyr in common lambsquarters compared with smooth pigweed at late growth stages was not explained by differential absorption, translocation, and metabolism. Since acetolactate synthase (ALS, or acetohydroxyacid synthase) (EC 4.1.3.18) is the target enzyme of imazethapyr, the activity of this enzyme was also examined in vivo and in vitro. In vitro studies showed higher ALS activity in extracts from common lambsquarters than smooth pigweed in the presence of the herbicide. However, the decreased efficacy of imazethapyr to common lambsquarters at late growth stages could not be accounted for by increased in vitro ALS activity. With the in vivo assay, common lambsquarters showed higher tolerance to imazethapyr at the recommended rate of 70 g/ha than smooth pigweed at every harvest in both experiments. This observation confirmed that the higher tolerance of common lambsquarters than smooth pigweed could, at least partially, be attributed to higher ALS tolerance to the herbicide. In addition, the amount of acetolactate synthesized in untreated plants increased with plant growth in common lambsquarters, suggesting that the greater enzyme activity present at the late growth stage than the early growth stage could contribute to common lambsquarters' tolerance to the herbicide.
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