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ARS Home » Midwest Area » Madison, Wisconsin » Vegetable Crops Research » Research » Research Project #434431

Research Project: Pollinators and Gene Flow

Location: Vegetable Crops Research

2018 Annual Report

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.

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. ARS scientists in Madison, Wisconsin planted the field experiments with a center glyphosate-resistant patch and four peripheral conventional patches of alfalfa of different sizes and distances from the center patch. The experiment was planted at three different locations at the West Madison Agricultural Research Station. This experiment will help determine how bumble bees choose the next patch they would move to. Transitions between patches by bees will be collected over the summer months to determine which patches bees move to most frequently from the center patch. We will compare the number of transitions to each conventional patch type to a random expectation using a Chi-square test. Objective 1, Sub-objective 1.2. ARS scientists in Madison, Wisconsin started the greenhouse experiments examining the response of honey bees to visual cues. To examine the preference of bees for visual cues we quantified the number of approaches and landings of bees on plants covered with clear plastic bags (visual only) relative to clear plastic bags without plants in them (control). We compared the number of visits to a random expectation using a Chi-Square test. Objective 2. ARS scientists in Madison, Wisconsin collected leaf tissue from various plants in four wild carrot populations in the vicinity of the carrot breeding area and four populations far away from the breeding area. Deoxyribonucleic acid (DNA) has been extracted from some of these samples and sequenced. Collaborators from Washington State, University of California at Fresno, and University of California, Agricultural and Natural Resources (UCANR) collected leaf and seed samples from 30 alfalfa seed-production fields throughout the alfalfa seed production areas in California and the Pacific Northwest. We threshed all the samples and counted the number of seeds per raceme and racemes per stem. In collaboration with an ARS scientist in Madison, Wisconsin, we are genotyping the leaf (or stem) and seed samples at various microsatellite loci. Using the progeny array genotypic data, the selfing rate of each field is estimated. To date, selfing rate estimates have been obtained for 12 fields, with the majority of these fields located in the Central Valley. Our collaborators also obtained data on diverse management practices used in these fields, and we will compile these data and format them for future statistical analyses. Current results have been presented at the North American Alfalfa Improvement Conference (NAAIC) in Logan, Utah. We examined the impact of the agricultural landscape on bee foraging behavior. We separately determined how patch size and isolation distance affected the foraging behavior of three distinct bee species foraging on alfalfa flowers. We examined various foraging behaviors and found impact of both patch size and isolation distance on some of these behaviors. For example, we obtained a significant effect of both field size and field isolation on residence or the number of flowers visited in a patch by a bee during a foraging bout. Bees visited more flowers in large patches and in more distant patches and this pattern was observed for all three bee species: bumble bees, honey bees and leafcutting bees. For a given bee species, greater residence is associated with lesser gene flow: these results indicate that such agricultural landscape features can help design field configuration to reduce gene flow in areas where both genetically engineered (GE) and conventional alfalfa are planted.

1. Field size and field isolation affect bee behavior and subsequent gene flow. Both field size and field isolation affected residence or the number of flowers visited by a bee in a field during a foraging bout. ARS scientists at Madison, Wisconsin found that bees visited more flowers in large patches and in far-away patches. This pattern was observed for all three bee species examined: honey bees, leafcutting bees, and bumble bees. Because higher residence reduces gene flow, results indicate that landscape configuration can be used to help reduce gene flow risk in areas where both genetically engineered (GE) and conventional alfalfa are grown in close proximity. This information is useful to farmers, the alfalfa seed industry, and the regulatory agencies concerned about adventitious presence in alfalfa seed-production fields.