Understanding the Interaction of Mesotrione and Atrazine in Redroot Pigweed (Amaranthus Retroflexus)
This dissertation covers an in-depth analysis on the interaction of mesotrione and atrazine and their impact on herbicide resistance stewardship and weed control efficacy. Mesotrione and atrazine are herbicides primarily used in corn, or maize. Herbicide resistance and a reduced number of new chemistries emerging to the market have led to an increased need in optimization and stewardship of currently-available herbicide portfolios. In this dissertation, the interaction of mesotrione and atrazine is investigated as a potential solution for increased longevity of use of mesotrione as an effective herbicide. Herbicide synergism between mesotrione and atrazine has demonstrated that efficacy of the two herbicides in mixture provide greater control of broadleaf weeds than either herbicide alone applied at particular rates. This herbicide synergism also persists in broadleaf weeds with a target site-based resistance to atrazine, thus, providing a potential reversal of atrazine resistance in these weed biotypes when atrazine is applied in mixture with mesotrione. Furthermore, an increased sensitivity to atrazine was observed in the target site-based atrazine resistant weed biotype at the whole-plant level as well as through chlorophyll fluorescence measurements, demonstrating a negative cross-resistance to the HPPD inhibitor mesotrione. While atrazine directly inhibits photosynthesis at photosystem II (PSII), mesotrione leads to the depletion of plastoquinone, a carrier molecule required to shuttle electrons from PSII, and carotenoids and tocopherols, which are antioxidants that protect from damage from excess energy evolving from photosynthesis. Analysis of the interaction of mesotrione and atrazine on a photosynthetic level using chlorophyll fluorescence for measuring damage to photosynthetic apparatus supports that the herbicides' synergy is based on an interaction of herbicidal effects within photosynthesis. Further studies investigating effects of mesotrione and atrazine using chlorophyll fluorescence demonstrated that mesotrione, which leads to depletion components involved in photosynthesis (carotenoids, tocopherols, and plastoquinone), has unique interactive effects with atrazine as a photosynthetic inhibitor, as compared with other herbicides that reduce levels of only carotenoids or carotenoids plus plastoquinone. Thus, a unique factor between HPPD-inhibitor (mesotrione) and PSII-inhibitor (atrazine) synergy is suggested to be the reduction of plastoquinone by the HPPD inhibitor mesotrione. These studies demonstrated that the proper use of herbicide interactions can help provide resistance management tools by controlling existing target site-based atrazine-resistant broadleaf weed populations and lead to longevity of use by avoiding overuse of herbicides of a single mode of action which selects for herbicide resistance.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign