Location: Vegetable Crops Research
2022 Annual Report
Objectives
Objective 1: Identify pollinator behaviors, pollinator management strategies, and crop production strategies that together mitigate unintended gene flow.
Sub-objective 1.1: Pollinator behavior and plant reproductive strategies affect gene flow risk.
Sub-objective 1.2: Visual and Olfactory cues that attract pollinators can guide the development of pollinator or crop management strategies that reduce gene flow and increase yield.
Objective 2: Determine the impacts of cultivated carrot genes on the genomic landscape of wild carrot.
Approach
Objective 1. This objective is divided into two sub-objectives, each with three hypotheses to be tested.
Sub-Objective 1.1. We will use a combination of field and greenhouse experiments to test the hypotheses within this subobjective. For example, the rules bees use when moving between patches or fields will be tested using patches of distinct sizes and isolation distances and measuring the number of transitions made by bees from a center glyphosate-resistant patch to the different conventional patches. The number of gene flow events in the different conventional patches, identified by the presence of glyphosate-resistant seeds, will also be used to test the decision making process of bumble bees. Greenhouse experiments will examine the pattern of seed deposition on flowers visited in succession by three bee species, honey bees, leafcutting bees and bumble bees. We will use glyphosate-resistant pollen donor and conventional pollen recipients and examine the number and proportion of glyphosate-resistant seeds on flowers visited in succession to determine the seed curve for each bee species.
Sub-Objective 1.2. To determine the preference of each of three bee species to visual and/or olfactory cues, we will perform greenhouse experiments and quantify approaches and landings to different visual and/or olfactory cues. To identify a blend derived from nest cells that attract leafcutting bees, we will capture and identify the chemicals present in the bee cell using Gas Chromatography-Mass Spectrometry (GC-MS); determine whether there is a behavioral response and then use couple gas chromatography – electroantennographic detection (GC-EAD) to identify physiological responses. Finally, the electrophysiologically active constituents will be tested using a behavioral assay.
Objective 2. We will use genotyping by sequencing on both cultivated carrots used in a breeding program and wild carrots in close proximity to the breeding area and far away to detect the presence of cultivated carrot genes in wild carrot populations. The presence of cultivated genes in wild populations represents introgression. We will determine the extent of introgression of cultivar genes in wild carrot populations.
Progress Report
Objective 1, Sub-objective 1.1.
Submitted a manuscript examining the potential risk of three bee species of moving glyphosate resistance genes when foraging on alfalfa.
Submitted a manuscript examining the degree of patch fidelity of honey bees and bumble bees and how this behavior affects plant reproduction and gene flow.
Submitted a manuscript linking the foraging behavior of three bee species to models of bee movement.
We are writing a manuscript examining the decision-making process of leafcutting bees when selecting patches. ARS researchers in Madison, Wisconsin, completed experiments linking the number of visits to a flower by a bee and pollen deposition on stigmas.
ARS researchers in Madison, Wisconsin, completed experiments linking the number of flowers visited by a bee and the amount of pollen on its body in the area likely to come into contact with the stigmas of alfalfa flowers.
Objective 1, Sub-objective 1.2.
Agricultural Research Service (ARS) and University of Wisconsin (UW) scientists in Madison, Wisconsin, pursued behavior experiments and determined the eletroantennogram (EAG) responses of Lygus hesperus to different scent compounds emitted by favored host plants.
Objective 2.
ARS researchers in Madison, Wisconsin, and collaborators have completed genotyping by sequencing (GBS) of wild and cultivated carrot cultivars, identified single nucleotide polymorphisms (SNPs), and performed the analyses to detect introgression of carrot cultivar genes into wild carrot populations.
University of Georgia collaborators and ARS researchers in Madison, Wisconsin, have determined best method for performing outcross crosses, and are growing plants in the greenhouse and will perform crosses when plants reach the flowering stage.
Land Institute collaborators, and ARS and Oakridge Institute for Science and Education (ORISE) scientists in Madison, Wisconsin, have collected first year data on the reproduction and pollination of feral alfalfa. ARS and ORISE researchers in Madison, Wisconsin, have performed a pilot experiment to determine the reduced water conditions under which alfalfa plants can survive and flower and the potential impact of reduced water on floral and reward traits in alfalfa.
Accomplishments
1. Bee species differ in their ability to move genes via pollen. Distinct bee species present distinct risk of spreading genetically engineered genes, and it is important to understand which aspects of their behavior create such differences. ARS researchers in Madison, Wisconsin, and colleagues examined the behavior of bees visiting alfalfa plants. The bees foraged on plants carrying the glyphosate resistance (GR) gene and were then moved to an array of conventional plants. Each flower visited by a bee was marked and recorded. Mature seeds were counted and tested for the presence of the GR gene. For each bee species, we determined the probability that a pod carried a GR seed as a bee moved among successive flowers. Leafcutting bees moved GR genes the shortest distances, and bumble bees the farthest, with honey bees being intermediary. Leafcutting bees produced the lowest number of GR genes in a foraging bout. These results correlate with field-based gene flow estimates for leafcutting bees and honey bees. Therefore, behavior of a bee species within a foraging bout helps predict gene flow risk in seed-production fields. This finding has important implications in terms of the bee species to use with GE crops to reduce gene flow risk.
2. Model of movement differs among bee species. In insect-pollinated plants, the foraging behavior of pollinators affects their pattern of movement. If distinct bee species vary in their foraging behaviors, different models may best describe their movement and a general model of bee movement cannot be applied to all bee species. ARS researchers in Madison, Wisconsin, and colleagues examined the fine scale movement of three bee species. Bee movement was described using distances and directions traveled between consecutive racemes. Bee species varied in their foraging behaviors. Bumble bees and honey bees traveled shorter distances after visiting many flowers on a raceme, while the distance traveled by leafcutting bees was independent of flower number visited by a focal bee. Bumble bees and honey bees showed directionality of movement within foraging bouts, meaning they tended to keep moving in the direction they started their foraging bout in. Leafcutting bees moved randomly between racemes. For each bee species, we tested four movement models that differed in how distances and directions were selected, and identified the model that best explained the movement data. The fine-scale, within-patch movement of bees could not always be explained by a random movement model, and a general model of movement could not be applied to all bee species. Movement models help predict spread of genetically engineered genes and it is important to identify the proper model to use for specific bee species.
