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ARS Home » Midwest Area » Madison, Wisconsin » Vegetable Crops Research » Research » Research Project #439213

Research Project: Impact and Spread of the Glyphosate Resistance Genes in Feral Alfalfa Populations

Location: Vegetable Crops Research

Project Number: 5090-21000-068-20-I
Project Type: Interagency Reimbursable Agreement

Start Date: Sep 1, 2020
End Date: Aug 31, 2022

The overall goal of this project is to quantify the frequency of the glyphosate resistance (GR) genes in feral alfalfa populations over a larger geographic scale, model the spread of these genes and quantify their impact on population growth rate, pollinators, pests and disease. More specifically, we will 1) extend the survey of feral populations for the GR genes to a larger geographical scale 2) estimate the frequency and change in incidence of the GR genes in feral populations, 3) quantify the impact of the GR genes on life-history parameters, pollinators, pests and disease of feral alfalfa, and 4) parameterize a population matrix model for GR and non-GR alfalfa.

We will survey a minimum of 200 sites in at least three states: California, Nebraska, and Wisconsin. The GPS location and population size of each site will be recorded, and leaf tissue will be collected from all plants in each population. Presence and type of management practices, for e.g. mowing, will be recorded for each feral population. Leaf tissue will be bulked and tested for the presence of the GR gene using commercially available strips. For bulks that tested positive we will use PCR and qPCR to measure the zygosity of the J101 and J163 events in each plant and obtain gene frequencies in each population. In at least three populations with the GR gene and three without within each state, we will collect data on pollinators, pests, disease and reproductive strategies. Each population with the GR gene will be paired with a population without the GR gene in an area. Populations with a minimum of 40 plants will be selected and with at least 50% of the plants carrying the GR gene for a GR population. Pollinators will be collected using net sweeping and pan traps. Net sweeps and observations will quantify pest presence and the presence and proportion of infested plants will be recorded. In these populations, all plants will be permanently marked and whether each plant is flowering or not will be recorded together with the size of each plant. Plant size will be quantified with its height and the diameter of its leaf tissue, and for the flowering plants, the number of stems, average number of racemes per stem and flowers per raceme will be recorded. Later in the season, at least 10 pods will be collected per plant and average seed set per raceme (pod) and total seed set per plant will be recorded. These same parameters will be measured the second year. Stages will be established based on the first- year data on plant size and we will build a stage matrix using seedlings, plants in stage 1, stage 2 and stage 3. By revisiting each of these populations over consecutive summers, we will quantify transitions between stages and reproductive effort and use these demographic data to parameterize a stage-based population matrix model and estimate ' for feral alfalfa with and without GR genes in state. The variable ' is a measure of population growth rate and is thus indicative of the invasiveness of these feral populations.