Phenotypic diversity for root traits andiIdentification of superior germplasm for root breeding in watermelon

Authors: Katuuramu, Dennis; Wechter, William - Pat; Washington, Marcellus; Horry, Matthew; CUTULLE, MATTHEW - Clemson University; Jarret, Robert - Bob; Levi, Amnon

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2020
Publication Date: 7/6/2020
Citation: Katuuramu, D.N., Wechter, W.P., Washington, M., Horry, M.I., Cutulle, M.A., Jarret, R.L., Levi, A. 2020. Phenotypic diversity for root traits andiIdentification of superior germplasm for root breeding in watermelon. HortScience. 55(8):12-72-1279. https://doi.org/10.21273/HORTSCI15093-20.
DOI: https://doi.org/10.21273/HORTSCI15093-20

Interpretive Summary: Watermelon is an important crop domesticated and consumed by people throughout the world for many decades. As a result of many years of domestication and selection for a watermelon with desirable fruit qualities, modern watermelon varieties have root systems smaller in size compared with those of their progenitor lines collected in the wild in Africa. The root systems of modern watermelon varieties are also highly susceptible to a wide range of soil-borne diseases. There is a need to improve the root capacity of modern watermelon varieties. In this study, Agricultural Research Service (ARS) scientists used a digital imaging technology to analyze the root systems of 335 watermelon accessions maintained at the USDA, ARS, Plant Genetic Resources Conservation Unit in Griffin, Georgia. The researchers found a wide diversity in root size and architecture of these watermelon accessions. They also identified several accessions with a robust root system that can be used in breeding programs aimed to improve the root system of modern watermelon varieties. This study provides valuable information to breeders and scientists working to improve watermelon.

Technical Abstract: Root traits are an important component for productive plant performance. Roots offer immediate absorptive surfaces for water and nutrient acquisition and are thus critical to crop growth and response to biotic and abiotic stresses. In addition, roots can provide the first line of defense against soil-borne pathogens. Watermelon crop performance is often challenged by inclement weather and environmental factors. A resilient root system can support the watermelon crop’s performance across a diverse range of production conditions. In this study, 335 3-day old watermelon (Citrullus spp.) seedlings were evaluated for total root length, average root diameter, total root surface area, and total root volume. Total root length varied from 8.78 to 181 mm (20.6-fold variation) and total surface area varied from 2 to 35.5 mm2 (17.7-fold variation). Average root diameter and total root volume had an 8 and a 29.5-fold-variation, respectively. Genotypes PI 195927 (Citrullus colocynthis) and PI 674448 (Citrullus amarus) had the largest total root length values. Accessions PI 674448 and PI 494817 (C. amarus) had the largest total root surface area means. Watermelon (C. lanatus) cultivars had a relatively smaller root system and significantly fewer fibrous roots when compared to the roots of the other Citrullus spp. Positive genetic correlations were identified among total root length, total root surface area and total root volume. This information will be useful in future breeding efforts to select for multiple root architecture traits in watermelon. Germplasm identified in this study that exhibit superior root traits can be used as parental choices to improve watermelon for root traits.