Date of Graduation

8-2024

Document Type

Thesis

Degree Name

Master of Science in Plant Pathology (MS)

Degree Level

Graduate

Department

Entomology and Plant Pathology

Advisor/Mentor

Correll, James C.

Committee Member

Rupe, John C.

Second Committee Member

Rojas, Alejandro

Third Committee Member

Bertucci, Matthew B.

Fourth Committee Member

Dhillon, Braham

Keywords

Cannabis sativa; Fungal diseases; Fungal genomics; Neofusicoccum parvum; Plant diseases

Abstract

Cannabis sativa has been an underutilized agricultural resource in the United States, largely due to federal regulations distinguishing marijuana from hemp. In 2018, Congress passed a Farm Bill, which defined hemp as C. sativa containing a tetrahydrocannabinol (THC) level of no more than 0.3%. As a result, commercial hemp production began in most states in 2019, including Arkansas, and was accompanied by numerous challenges like diseases and pests. The research on the epidemiology of diseases affecting C. sativa is limited, and understanding the pathogens is in its early stages in the U.S. For this study, an initial disease survey was conducted in 2020, 2021, and 2022 in Arkansas, California, and Oklahoma at various commercial hemp production sites. Plants showing signs and/or symptoms were collected for diagnosis, with pathogen recovery and identification to species-level based on morphology as well as molecular analysis. A focus of the thesis was on a newly identified disease, terminal or branch dieback of hemp, caused by the fungus Neofusicoccum parvum, identified in Arkansas for the first time in the U.S. in 2019. A subset of representative isolates from hemp and non-hemp hosts, and closely related species, selected from a larger collection of isolates was examined for the etiology and pathogenicity on hemp and several other reported hosts like, blueberry (Vaccinium sp.), oak (Quercus sp.), blackberry (Rubus fruticosus), and grape (Vitis labrusca). Additionally, the subset of isolates was examined for molecular diversity, morphological characteristics, and optimal growth temperatures. Whole genome sequencing was performed on four reference isolates of N. parvum from hemp using Illumina sequencing. Comparative genomics was then conducted between the hemp isolates and isolates of N. parvum from grape, pear, and mango obtained from other geographical locations. Although there was considerable variation in the criteria examined, hemp isolates of N. parvum were quite similar to other non-hemp isolates and closely related species. The thesis represents the first research effort on diseases of hemp in Arkansas.

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