Location: Crop Production Systems Research
2023 Annual Report
Objectives
1. Determine differences in seed biology and fitness characteristics, such as competitiveness, photosynthetic capacity, responses to stress, and other growth- related factors of herbicide-susceptible versus herbicide-resistant weed biotypes.
1A. Determine differences in fitness characteristics, such as competitiveness, photosynthetic capacity, and responses to stress factors in herbicide-susceptible versus herbicide-resistant weed biotypes.
1B. Determine differences in fitness characteristics, such as competitiveness and responses to stress factors in herbicide-susceptible versus herbicide-resistant weed biotypes.
1C. Determine differences in fitness characteristics, photosynthetic capacity, and responses to stress factors in herbicide-susceptible versus herbicide-resistant weed biotypes.
1D. Comparison of whole-plant physiological processes of herbicide resistant weed populations with corresponding susceptible populations.
1E. Comparison and characterization of pigment contents and antioxidant capacities of red and green biotypes of glyphosate-resistant Palmer amaranth plants and their responses to selected herbicides and a bioherbicide.
2. Discover and characterize patterns of herbicide resistance in weed populations, elucidate underlying physiological, biochemical, and molecular mechanisms for use in identifying unique biological features that define their “weediness”, and explore their utility for developing control strategies.
2A. Discover and characterize patterns of herbicide resistance in weed populations.
2B. Elucidate underlying physiological, biochemical, molecular mechanisms of resistance to herbicides in weed populations where the level and nature of resistance is known.
2C. Discover and develop new approaches to weed control based on development of molecular herbicides specifically targeting our most troublesome weeds.
3. Identify key additive and/or synergistic interactions of combinations of chemicals, natural products and/or plant pathogens with herbicides to manage or control herbicide resistant weeds.
4. Evaluate for efficacy novel herbicide drift management and application techniques, emerging commercial herbicide or herbicide resistant crop technologies, and weed control methods such as microwave and steam.
4A. Evaluation of a novel fluorescent compound for measuring herbicide drift.
4B. Evaluation of unmanned aerial vehicle (UAV) technology for detection and management of herbicide-resistant weed populations and herbicide drift issues.
4C. Evaluation of emerging commercial herbicide and or herbicide resistant crop technologies.
4D. Evaluate the efficacy of microwave weed control methods.
Approach
The overall project goal is to discover basic and practical knowledge of the occurrence, distribution, mechanism of resistance and management of weeds that are difficult to control or that have evolved resistance to one or to multiple herbicides. This broad-scope approach will lead to more effective weed control methods and novel weed control management practices. The development of new weed management tools, aided by knowledge of resistance mechanisms and weed biology will advance the development of sustainable practices for early detection and management of weeds and facilitate the development of strategies to provide more efficacious weed control via integrated use of chemical, mechanical, biological and cultural methods.
Through basic analyses, assays and bioassays of whole plants and plant tissues from laboratory, greenhouse and field experiments will determine major differences in resistant versus susceptible weed biotypes. Subsequent biochemical, genetic, proteomic, immunochemical and radiological studies will identify and characterize specific site differences in herbicide resistant and sensitive weed biotypes within species. Experiments on the development of novel mechanical weed control methods and weed control using bioherbicides will provide important results that could substantially lower the amount of herbicide usage. The knowledge generated from these experiments will provide a greater understanding of the biochemistry, physiology and genetics of resistance mechanisms and provide insight for recommendations that will promote efficacious and sustainable weed control coupled with more efficient and economic crop production with reduced herbicide usage and impact on the environment.
Progress Report
Studies continued on the antioxidant capacity of two (red-pigmented and green-pigmented) glyphosate -resistant Palmer amaranth biotypes that exhibit different betalain pigment profiles. Data on phenolic compound levels, various assays for antioxidant/reducing potential, oxidative enzyme activity and tolerance/susceptibility to herbicides (acifluorfen, paraquat and atrazine) are being summarized and a manuscript is being drafted.
Gibberellic acid (GA) and glyphosate effects on growth and phenolic metabolism using soybean as a model plant indicated both GA and glyphosate caused increased phenylalanine ammonia-lyase activity (PAL) above control levels, and GA plus glyphosate treatments resulted in additive increases of PAL activity. GA increased hypocotyl and epicotyl elongation and caused marginal reversal of glyphosate inhibition of elongation of these organs. Results were summarized and a manuscript is in journal review. Extended research on GA interactions with bioherbicides/herbicides was initiated.
Studies on interactions of phenoxy herbicides and a fungal bioherbicide (Fusarium lateritium) showed that combinations of 2,4-DB and the fungus were synergistic for the control of the weed, velvetleaf. Results have been summarized and a manuscript is being prepared.
Studies on glyphosate-resistant horseweed (Conyza canadensis) control with a fungal bioherbicide (Albifimbria verrucaria) continued and a manuscript is in journal review.
Continued research on a bioherbicide (Colletotrichum gloeosporioides) that causes high efficacy (mortality and growth reduction) on the weed, cutleaf geranium (Geranium dissectum). Data were summarized and manuscript is in journal review.
Studies continued on two distinct biotypes of Palmer amaranth that differ in betaxanthin and betacyanin pigment levels. The finding that betaxanthin emits fluorescence is an important physiological property and its distribution in plant organs of these biotypes is being assessed.
Accomplishments
1. Plant growth regulator and herbicide interactions. ARS researchers in Stoneville, Mississippi, found important interactions of gibberellic acid (GA) and glyphosate on growth and phenolic metabolism using soybean as a model plant. Laboratory studies showed both GA and glyphosate caused increased phenylalanine ammonia-lyase activity (PAL) above control levels throughout a 96-hr time course, and GA plus glyphosate treatments resulted in additive increases in PAL activity. GA increased hypocotyl and epicotyl elongation and caused marginal reversal of glyphosate inhibition of elongation of these organs. Results show some differential effects of GA and glyphosate interactions on growth and phenolic metabolism that provide impetus for further research of GA with herbicides and/or bioherbicides to discover synergistic formulations for improved weed control.
