Date of Award

9-1-2025

Degree Type

Thesis

Degree Name

Master of Science (M.S.)

Department

Agricultural and Environmental Sciences

First Advisor

Ahmad Aziz

Abstract

Herbicide-resistant weeds pose an escalating threat to crop productivity in Tennessee, leading to notable economic losses and complicated conventional weed control strategies. Among the most persistent species, Sorghum halepense (Johnsongrass) and various Amaranthus species (pigweeds) have exhibited remarkable adaptability and increasing resistance to widely used herbicides. Addressing this growing issue necessitates a thorough understanding the genetic and biochemical mechanisms that drive herbicide resistance. This study conducted an extensive genetic analysis of Pigweed and Johnsongrass samples collected from a broad range of counties across Tennessee, ensuring representation from both the northern and southern portions of the state’s Eastern, Central, and Western regions. Genomic DNA was extracted and subjected to PCR-based molecular assays for species verification. EPSPS (5-enolpyruvylshikimate-3-phosphate synthase)-based enzymatic assays were used to assess the degree of herbicide resistance. Additionally, Johnsongrass samples were analyzed using Kompetitive Allele-Specific PCR (KASP) to detect SNPs linked to agronomic traits. PCR amplification was successful across most regions, with Johnsongrass showing a higher amplification rate (85.41%) than pigweed (74.50%). EPSPS activity in Johnsongrass varied regionally, peaking in the Central region (76.9%), followed by the Eastern (69.2%) and Western (64.1%) zones. In contrast, pigweed exhibited consistently high EPSPS activity across all regions, suggesting advanced glyphosate resistance. KASP profiling of 129 samples using 16 sugar-related markers revealed over 90% success and high heterozygosity (60–80%), indicating genetic diversity. The future addition of 20 growth vigor markers is expected to enhance our understanding of weed competitiveness and support the development of more targeted, sustainable weed management strategies across Tennessee.

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