Date of Graduation

5-2022

Document Type

Thesis

Degree Name

Master of Science in Horticulture (MS)

Degree Level

Graduate

Department

Horticulture

Advisor/Mentor

Worthington, Margaret L.

Committee Member

Lee, Jacquelyn A.

Second Committee Member

Douglas, Marlis R.

Third Committee Member

McDonald, Garry V.

Keywords

Genetics; Grape; Muscadine; Population Structure; Propagation; Rooting

Abstract

The muscadine (Vitis rotundifolia syn. Muscadinia rotundifolia) is a grape species native to the southeastern United States. Muscadines are one of three grape species in subgenus Muscadinia with a chromosome number of 2n=40 (V. rotundifolia, V. munsoniana, and V. popenoei), making them genetically distinct from the European wine and table grape (Vitis vinifera) and other species in subgenus Euvitis. Rooting hardwood cuttings from muscadine vines has traditionally been considered an exceptionally difficult task. Many previous studies observed almost no root formation, leading to a general consensus that muscadines should either be propagated by softwood cuttings or vegetative layering. However, the University of Arkansas System Division of Agriculture Fruit Breeding Program has been using a hardwood rooting protocol for muscadines with moderate success for the past ten years. The first chapter of this thesis investigated the effects of cultivar, bottom heat, cold storage, vineyard location, and cutting collection date on the outcome of muscadine hardwood cuttings. The study was conducted during the dormant seasons of 2019-2020 and 2020-2021, and an overall rooting percentage of 16% was observed. There were multiple higher-order interactions affecting rooting efficacy. Cuttings taken in November generally rooted at higher rates, although interactions with vineyard location and cultivar played a significant role in those results. The Ocilla, GA location performed exceptionally well in November with rooting percentages of over 40%. The effects of supplying bottom heat and/or a cold storage treatment on rooting success declined as the dormant season progressed. Other variables such as increased cutting length and diameter were associated with increased rooting success. Ultimately, this research shows that institutions with modest muscadine propagation needs can successfully propagate plants from hardwood cuttings. Muscadine breeding has been continuous since the late 19th century, yet the germplasm that served as the foundation for early breeding efforts was sourced almost exclusively from the coastal plains of North Carolina. The second chapter of this thesis investigated the diversity of wild and cultivated muscadine populations. We used the rhAmpSeq Vitis core panel haplotype markers to genotype 194 Muscadinia accessions from five cultivated populations and 15 wild populations collected across their native range. Wild populations from the western half of the native range were generally less genetically differentiated than hypothesized, but were genetically distinct from the material used in both past and present breeding efforts. One population collected from coastal North Carolina grouped closely with Vitis munsoniana accessions despite being well outside the reported range for that species. Principal coordinate and structure analyses revealed three main groups within the 194 accessions. At K=5, structure results showed that more recent muscadine cultivars are further differentiated from wild accessions and varieties. These analyses confirmed our hypothesis that muscadine cultivars are genetically differentiated from their wild counterparts. This study also showed that genetic diversity in V. rotundifolia is not equally distributed across its native range and that the limited number of genotypes used in crop improvement efforts have not fully utilized the genetic diversity within the species.

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