Abstract

Growing food in urban spaces often means working within variable, resource-limited environments, creating a need for crops that can withstand heterogeneous growing conditions. Heirloom collards (Brassica oleracea var. viridis) are known for their aboveground diversity and cultural importance, but much less is known about the variation that exists belowground. This dissertation examines root system architecture (RSA) diversity across 19 historically underutilized heirloom collard accessions using a multi-scale phenotyping approach that includes controlled gel-based imaging of seedlings and 2D imaging of mature field-grown root systems. Across both seedling and mature stages, heirloom collards showed substantial variation in RSA. These differences revealed multiple strategies for soil exploration, biomass allocation, and root branching. Comparisons between seedling and mature-stage populations showed that seedling root systems were more flexible, with traits that were less tightly connected to one another, while mature root systems showed stronger trait relationships. Several accessions that appeared less distinct in the seedling analysis exhibited more complex root systems at maturity, highlighting the importance of evaluating roots across developmental stages. To better understand the genetic basis of RSA variation, an F₁ mapping population was developed using a nested diallel mating design with Georgia, a commonly grown open-pollinated variety, as the common maternal parent. Paternal donor identity significantly influenced progeny root phenotypes, suggesting that RSA traits are quantitatively inherited and shaped by specific genetic backgrounds. Together, these findings show that heirloom collards contain previously undocumented belowground diversity that may be useful for crop improvement. This work suggests that breeding climate-resilient collards for urban and low-input agroecosystems may require attention to a range of mature root phenotypes rather than a single ideal root architecture.

Committee Chair

Christopher Topp

Committee Members

Julie Dawson; Kristine Callis-Duehl; Malia Gehan; Rachel Penczykowski

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Plant & Microbial Biosciences)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

8-19-2026

Language

English (en)

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