Citrullus amarus Drought Tolerance: An Above and Below Ground Analysis

Author

Ben A. Hyland, Clemson UniversityFollow

Date of Award

12-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Plant and Environmental Science

Committee Chair/Advisor

Brian Ward

Committee Member

Sandra Branham

Committee Member

William Bridges

Committee Member

Matthew Cutulle

Abstract

Ever rising environmental temperatures threaten global food security by worsening severity and increasing the occurrence of drought. Commercially cultivated watermelon (Citrullus lanatus), have reduced drought tolerance due to a narrow genetic base caused by breeding for desirable traits such as sweetness, size, and flesh/rind color. Comparatively, the crop wild relative desert watermelon variety (Citrullus amarus), while more drought tolerant than their commercially cultivated relatives (C. lanatus), still require large amounts of water to grow and produce reliable fruit yields. Watermelon root morphology plays a key role in their ability to tolerate drought, with more extensive root architecture (length, volume, surface area, and diameter) allowing for more efficient water utilization, especially when water is scarce. The root architecture of 122 accessions of Citrullus amarus were screened using a WinRhizo root and shoot scanner in a greenhouse setting. The results indicate significant differences between the accessions, each one having distinct root and shoot lengths, volumes, surface areas, and diameters. Furthermore, certain accessions stood out from the rest as having exceptionally large or small root systems. Additionally, a genome-wide association study (GWAS) was performed to identify significant SNPs associated with the previous four types of root data. We report broad sense heritability for each of the four types of root and shoot data as well as scatter plots highlighting the top 5% and bottom 5% accessions for both root and shoot length, volume, surface area, and diameter.

Consecutively, the top 2, middle 2, and bottom 2 accessions from the 122 screened in the Hyland et al. (2025) WinRhizo root architecture study were selected based on root length, the morphological quality most significantly affecting drought resistance. These 6 accessions (referred to as 1 – 6 based on size of root architecture, largest to smallest) were grown in a greenhouse setting and analyzed for plant response qualities related to drought stress (stomatal conductance, transpiration rate, and carbon assimilation) using a LICOR – 6800 portable photosynthesis system. It was observed that all PIs had a large drop off across all plant response values regardless of treatment (drought or no drought) around scan 4 out of 9 (coinciding with about 4 – 5 weeks since seeding). This widespread drop off was likely caused by a lack of nitrogen access resulting from no added fertilizer at any point, a decision made to avoid added salt stress on the stomata effecting stomatal conductance results. Results include tracking physiological responses that are heavily impacted by drought stress (stomatal conductance, transpiration rate, and carbon assimilation) for all PIs across 9 total scans (3 scans per week). Additionally, supplemental data such as fresh and dry weight, vine length, leaf surface area, and leaf count were taken at the end of the study and added necessary context to the physiological results.

Recommended Citation

Hyland, Ben A., "Citrullus amarus Drought Tolerance: An Above and Below Ground Analysis" (2025). All Theses. 4642.
https://open.clemson.edu/all_theses/4642