Location: Crop Production Systems Research
2022 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
The sequence of circular DNA content in the replicon of glyphosate-resistant Palmer amaranth from geographically distant populations was characterized. The replicon is a feature of the glyphosate-resistant pigweed genome that gives the weed selective advantage to survive and proliferate and it has characteristics similar to some human cancers. Results were summarized and published.
Studies on the effects of the fungal bioherbicide, Alternaria cassiae on peroxidase, pectinolytic and proteolytic activities in the weed sicklepod suggested some of these enzymes may be involved in resistance/defense against pathogen attack. This novel information provides impetus for further molecular biology research on these pathogen:weed interactions. Results have been summarized and published.
A 3-year study on a winter rye-soybean summer cover crop rotation system demonstrated that a winter rye cover crop, followed by summer soybean cash crop, is agronomically feasible and offers a sustainable management option for the soybean growers. Data on rye cover crop effects on weed control/management, soybean yield and profitability was summarized and published.
Studies on a bioherbicidal isolate of Myrothecium verrucaria that has been extensively studied in our laboratory resulted in re-classifying the organism as, Albifimbria verrucaria. These morphological and genetic analyses have been summarized and published.
Studies on branching configurations of five new cotton varieties demonstrated variance. Differences in branching patterns and spacial arrangements of bolls may contribute to differences in canopy closure and harvesting efficiency and should be considered in variety selection processes. Data has been summarized and submitted for publication.
The bioherbicidal fungus, Albifimbria verrucaria (formerly Myrothecium verrucaria) was found to be efficacious against glyphosate-resistant and -susceptible horseweed (Conyza canadensis) when applied as a mycelial formulation under greenhouse and field conditions. Results indicate that this fungus can infect and kill horseweed, demonstrating its bioherbicidal potential on this important aggressive weed that has evolved resistance to multiple herbicides.
Cutleaf geranium (an introduced weed), has become an early season weed in the U.S. Collaborative studies demonstrated the fungus (Colletotrichum gloeosporioides) caused significant mortality and growth reduction to weed seedlings and that a dew period was required to cause infection under greenhouse conditions. Experiments showed the environmental conditions for optimal control of this weed would occur in early-mid-spring. Results have been summarized for publication.
Studies continued on two major Palmer amaranth biotypes (red pigmented and green-pigmented), both resistant to glyphosate. Bioassays of the biotypes showed differential tolerances to three herbicides that may be related to pigmentation differences or to other biochemical mechanisms of tolerance.
Accomplishments
1. Replicon characterization in glyphosate-resistant Palmer amaranth. ARS researchers in Stoneville, Mississippi, and Clemson University, continued molecular research on the unique extra-chromosomal circular DNA structure (the replicon of glyphosate-resistant Palmer amaranth), which contains the EPSPS gene (target of glyphosate), to more clearly understand the molecular genetics of glyphosate resistance in this major weed. RNA sequencing experiments were completed on the replicon to determine the number of genes of the replicon that were amplified and expressed. The function and assay of known genes will be determined to elucidate the overall functionality of the replicon and its relationship to inheritance, breeding, biotechnology and to human circular DNA.
2. Bioherbicidal control of weeds. ARS researchers in Stoneville, Mississippi, discovered that a fungal bioherbicide, Albifimbria verrucaria (formerly Myrothecium verrucaria) had potential as a biocontrol agent against Conyza canadensis (horseweed). Horseweed is problematic due to aggressive growth traits and resistance to several herbicides, including glyphosate. A. verrucaria was efficacious against glyphosate-resistant and – susceptible horseweed plants when applied as a mycelial formulation under greenhouse and field conditions. Rosette leaf-stage plants were more susceptible, but the fungus provided ~95-100% control of bolting plants under greenhouse conditions. Field tests of plants in the bolting/inflorescence stage showed less efficacy. Results indicate that this fungus can infect and kill horseweed and suggest improved formulation may be required to improve efficacy under field environments.
3. Weed: pathogen interactions. Numerous reports demonstrate the control of weeds using bioherbicides, but there is sparse information on the enzymes involved in pathogen:weed interactions related to weed resistance/defense mechanisms. ARS researchers in Stoneville, Mississippi, investigated the interactions of (Alternaria cassiae) and its host weed (sicklepod) with respect to various enzyme activities. Peroxidase and pectinolytic activities were elevated in seedling tissues early after inoculation with the bioherbicide suggesting possible involvement in the resistance/defense against pathogen attack. This information provides impetus for further molecular biology research useful for improvements to biological weed control programs utilizing plant pathogens.
Review Publications
Hoagland, R.E., Boyette, C.D. 2021. Effects of the fungal bioherbicide, Alternaria cassia on peroxidase, pectinolytic and proteolytic activities in sicklepod seedlings. The Journal of Fungi. https://doi.org/10.3390/jof7121032.
Pinnamaneni, S.R., Saseendran, A., Molin, W.T., Reddy, K.N. 2022. Effect of cereal rye cover crop on weed control, soybean yield and profitability. Frontiers in Agronomy. https://doi.org/10.3389/fagro.2022.907507.
Weaver, M.A., Hoagland, R.E., Boyette, C.D., Brown, S.P. 2021. Taxonomic evaluation of a bioherbicidal isolate albifimbria verrucaria, formerly myrothecium verrucaria. The Journal of Fungi. 7(9):694. https://doi.org/10.3390/jof7090694.
