INVESTIGATING THE ROLE OF PHENOTYPIC VARIABILITY IN LOCAL ADAPTATION OF A NATIVE AGRICULTURAL WEED, AMBROSIA TRIFIDA (GIANT RAGWEED)

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1021813
• Project Start Date: Dec 12, 2019
• Project End Date: Sep 30, 2024
• Program Code: [(N/A)]- (N/A)

Recipient Organization
OHIO STATE UNIVERSITY
1680 MADISON AVENUE
WOOSTER,OH 44691

Performing Department
Horticulture and Crop Science

Non Technical Summary
Giant ragweed is a major agricultural weed of row crops in the U.S. and a principal source of allergenic pollen that adversely affects one in five U.S. citizens.As a native plant of riparian and other non-agricultural habitats in North America, giant ragweed exhibits a high degree of phenotypic variability, and its well-documented, rapid development of resistance to several different herbicides suggests it has a high degree of genetic variation and evolvability in other traits.The spread of traits advantageous to giant ragweed have no doubt contributed to its continued success as an agricultural weed and therefore warrant detailed investigation in order to gain a better understanding of 1) how it first invades agricultural fields and 2) how it becomes adapted to modern crop production practices.We aim to study phenotypic factors that contribute to giant ragweed's weedy behavior and determine the role of seed size and seedling emergence duration as adaptations to current agricultural practices.A better understanding of the ecological effects of giant ragweed genotypic and phenotypic variability will lead to better preventive and management strategies that will reduce its prevalence in agricultural fields.

Animal Health Component

100%

Research Effort Categories

Basic

(N/A)

Applied

100%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
213	1599	1140	100%

Knowledge Area
213 - Weeds Affecting Plants;

Subject Of Investigation
1599 - Grain crops, general/other;

Field Of Science
1140 - Weed science;

Keywords

ambrosia trifida

giant ragweed

phenotypic variability

allergen

weed adaptation

Goals / Objectives
The overallgoalof this project is to characterize phenotypic variation in giant ragweed and determine its potential role in driving giant ragweed's introduction and spread in agricultural fields.Objective 1: To quantify and characterize phenotypic variation in giant ragweed seed morphology in locally adapted successional vs. agricultural field populations.Objective 2: To determine the extent to which variation in giant ragweed fecundity, seed size, and seedling emergence duration contribute to variation in local adaptation.

Project Methods
Procedures for Objective 1: Twenty pairs of giant ragweed populations, representing successional and agricultural populations selected within a 0.1-km radius of each other at each of 20 sampling sites, will be established on a uniform soil at the research station. Sampling sites will be selected along an east-west transect from Columbus, OH to the Indiana border and will be spaced a minimum of 5 km apart. At each sampling site we will collect seeds from a giant ragweed population in an agricultural field and from a nearby (within 0.2 km) non-crop habitat (e.g., riparian, forest edge, or perennial grass-dominated habitat). Giant ragweed population density, height, and shoot biomass/area will be sampled from six randomly placed 0.25 m2quadrats just prior to anthesis in each population. At weed maturity in October, seeds will be collected from 20 plants selected randomly from each population. Twenty filled seeds per plant will be selected at random for morphometric measurements using ImageJ software. Morphometric measurements of seeds will include area, length:width ratio, convexity (convex hull perimeter/fruit perimeter), and solidity (fruit area/convex hull area) (Hovick et al., 2018).Nested analysis of variance will be conducted to determine significant differences in seed morphology characteristics among sampling sites, habitats, and individual plants. The percent of total variance attributable to each factor will be determined. Orthogonal contrasts will be used to determine the effect of sampling site and habitat on seed morphological characteristics and on within-population variation in seed morphology.Procedures for Objective 2: A common garden seedling emergence duration experiment will be conducted at the Western Agricultural Research Station of the Ohio Agricultural Research and Development Center located in west-central Ohio. Seeds collected from sites described in Objective 1 will serve as the source material. The field experiment will be composed of a factorial treatment arrangement consisting of 20 sampling sites (east-west transect from central OH to the Indiana border) x 2 habitats (agriculture vs. successional) x 3 replicates = 120 plots arranged in a randomized complete block design. Each plot will be 9 square m and be seeded with 500 seeds/plot in late October the year of seed collection to allow for cold stratification over the winter. Weekly giant ragweed seedling emergence monitoring will commence beginning in early March and continuing throughout the summer each year, with seedlings being removed after they emerge. Emergence data will be analyzed as described for objective 1; in addition, nonlinear regression models will be fit to the emergence data as described in Schutte et al. (2012).

Progress 12/12/19 to 09/30/20

Outputs
Target Audience: Agriculture professionals in the public and private sector, Certified Crop Advisers, and weed scientists in academia and industry Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?We will conduct addition analyses of paired agricultural vs. riparian giant ragweed populations sampled from Ohio, then publish the results of our finding in a peer-reviewed journal and the appropriate extension newsletter.

Impacts
What was accomplished under these goals? Giant ragweed (Ambrosia trifida) initially became established as a weed in crop fields with flood plain transition to agriculture, but over the past 30 years its range has been expanding outward into crop fields across the U.S. Corn Belt to Colorado in the west, Ontario in the north, and Mississippi in the south. In a common garden experiment, we investigated variability in intraspecific fecundity, seed morphology, and seedling emergence characteristics among giant ragweed populations sampled from the U.S. Corn Belt along an east-west gradient, which we hypothesize has been the direction of giant ragweed spread as an agricultural weed over the past several decades. Paired populations (agricultural and non-agricultural, riparian habitats) were sampled from seven regions ranging from central Ohio in the east to southern Minnesota in the west. Giant ragweed populations on the western invasion front had four-fold greater fecundity and allocated 50% more biomass to reproductive allocation than Ohio populations, reflecting an inverse relationship between fruit size and fruit number across the region. This trade-off may have the net effect of increasing propagule pressure near the western invasion front compared to eastern populations. On a smaller scale, giant ragweed seedlings from agricultural populations were smaller and emerged later than those from riparian populations; however, total fecundity did not differ between habitats because agricultural populations had greater reproductive allocation than riparian populations. Giant ragweed's adaptive potential and apparent phenotypic plasticity appear to play an important role in its spread as an invasive weed.

Publications