Date of Graduation

8-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Agricultural, Food and Life Sciences (PhD)

Degree Level

Graduate

Department

Entomology and Plant Pathology

Advisor/Mentor

Rupe, John C.

Committee Member

Rojas, Alejandro

Second Committee Member

Spurlock, Terry

Third Committee Member

Purcell, Larry C.

Fourth Committee Member

Shi, Ainong

Keywords

Pthogen; Fungus; Soybean

Abstract

This study evaluated the effects of planting date (PD), seed vigor, and chemical seed treatments on the plant stand and yield of two soybean cultivars with different maturity groups (MGs) across four locations in Arkansas from 2018 to 2021. Early planting in early May (early PD) led to higher plant stands and yields compared to late planting in early June (late PD). The interaction between planting date and cultivar was significant, with both cultivars showing higher plant stands on early planting dates. Seed vigor and seed treatment also significantly impacted plant populations; high-vigor seeds planted early resulted in better stands than low-vigor seeds planted late. Seed treatments generally improved plant stands, although some treatments containing metalaxyl and thiamethoxam negatively affected seed germination and seedling survival. These findings highlight the importance of planting date, seed vigor, seed treatment, and cultivar selection in optimizing soybean production in Arkansas. Additionally, the study investigated the impact of environmental conditions and fungicide treatments on seed-borne pathogens like Diaporthe seed decay (DSD) and purple seed stain (PSS). Field trials demonstrated that foliar fungicides, especially pyraclostrobin, were effective in reducing DSD and PSS, despite conducive warm and wet conditions. Cercospora spp. negatively influenced certain seed components, while Diaporthe spp. infections correlated positively with oil content and specific amino acids. Furthermore, the research analyzed the fungal community and taxonomic composition of soybean seeds across developmental stages, locations, and years, identifying 2,674 unique fungal operational taxonomic units (OTUs) from 175 samples. Significant variations in fungal richness and diversity were primarily driven by seed development stages. Despite fungicide treatments reducing some fungal genera, these remained present in harvested seeds. This study provides insights into the soybean seed microbiome, showing significant differences due to seed phenology, locations, years, and cultivars, while indicating similar impacts of different fungicide active ingredients on seed microbiome assembly.

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Available for download on Friday, September 12, 2025

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