Breeding Watermelon for Human Nutrition

New Flesh Colors and Nutrients

by Todd C. Wehner
Department of Horticultural Science
North Carolina State University
Raleigh, NC 27695-7609

Introduction

Watermelon flesh color is controlled by several genes to produce scarlet red, coral red, orange, salmon yellow, canary yellow, or white. Genes conditioning flesh colors are B, C, i-C, Wf, y, and y-o. Canary yellow (C) is dominant to other colored flesh (c). Coral red flesh (Y) is dominant to salmon yellow (y). Orange flesh (y-o) is a member of multiple allelic system at that locus, where Y (coral red flesh) is dominant to both y-o (orange flesh) and y (salmon yellow), and y-o (orange flesh) is dominant to y (salmon yellow). In a separate study, two loci with epistatic interaction controlled white, yellow, and red flesh. Yellow flesh (B) is dominant to red flesh. The gene Wf is epistatic to B, so genotypes WfWf BB or WfWf bb were white fleshed, wfwf BB was yellow fleshed, and wfwf bb was red fleshed. Canary yellow flesh is dominant to coral red, and i-C inhibitory to C, resulting in red flesh. In the absence of i-C, C is epistatic to Y.

A single dominant gene, Scr, produces the scarlet red flesh color of ‘Dixielee’ and ‘Red-N-Sweet’ instead of the lighter, coral red (scr) flesh color of ‘Angeleno Black Seeded’. Additional studies are needed to determine the interaction of Scr with Y, y-o and y, and the interaction of C with Y, y-o and y.

Although flesh color is shown to be controlled by single genes, the fruit in a segregating generation from a cross between two different inbreds is often confusing. Often there are different flesh colors in different areas of the same fruit. One possible hypothesis to explain the presence of the abnormal types is that the expression of the pigment is caused by several different genes, one for each area of the fruit. Thus, the mixed colorations would have been caused by recombination of these genes. It may be useful to have a separate rating of the color of different parts of the flesh to determine whether there are genes controlling the color of each part: the endocarp between the carpel walls and the mesocarp (white rind); the flesh within the carpels, originating from the stylar column; and the carpel walls.

Human nutrition

Lycopene
- Watermelon is a good source of antioxidants (lycopene), arginine, and the arginine precursor, citrulline. Lycopene is a red-pigmented carotenoid with antioxidant properties that serves as an intermediate for the biosynthesis of other carotenoids. In red-fleshed watermelon, lycopene accounts for 70 to 90% of the total carotenoids, the remainder consisting of phytofluene, phytoene, β-carotene, lutein, nerosporene, and ζ-carotene. In orange-fleshed watermelon, prolycopene, phytoene, and ζ-carotene are the major carotenoids. In canary yellow and salmon yellow fleshed watermelons, neoxanthin is the major carotenoid. Studies have shown that the content of lycopene and carotenoids increases rapidly and accumulates 10 to 12 days after pollination in diploid watermelons, and continues to accumulate as the fruit mature.
- In humans, lycopene reduced cancer cell growth and induced cell death in malignant leukemia, endometrial, mammary, lung, and prostate cancer cells. Lycopene protected against lipid peroxidation and foam cell production, which are implicated in the initiation of atherosclerosis. A diet consisting of fruits and vegetables rich in lycopene can protect against stroke and cardiovascular diseases. Watermelon juice containing lycopene and citrulline may improve athlete recovery and performance.
Citrulline
- Citrulline is present in some cucurbits, including watermelon. It belongs to the L-arginine metabolic family. In related Citrullus species, citrulline content increases in the foliage during drought stress, and may improve plant tolerance to stress. In melon, foliage citrulline content is an important indicator for drought stress. In developing watermelon fruit, citrulline content is low, reaching peak levels just before maturity, and declining as the fruit age. Citrulline content tends to be higher in canary yellow watermelons.
- In humans, citrulline helps in muscle recovery during exercise, and benefits vascular health, such as reducing blood pressure, and increasing vasodilation in many tissues of the body, which helps mitigate cardiovascular disease.

The morphological and resistance genes of watermelon, including gene symbol, synonym, description, references, availability (y), and photograph.(z)

Symbol	Gene description and type lines	Human nutrition	Photograph (click for larger image)
C	Canary yellow flesh; dominant to pink; i-C inhibitory to C, resulting in red flesh; in the absence of i-C, C is epistatic to Y; CC from ‘Honey Cream’* and NC-517, cc from ‘Dove’; CC YY I-C I-C* from ‘Yellow Baby’ F1 and ‘Yellow Doll’ F1; cc yoyo I-C I-C from ‘Tendersweet Orange Flesh’*; cc yy I-C I-C* from ‘Golden Honey’*; cc YY i-C i-C* from ‘Sweet Princess’**.	Citrulline
Scr	Scarlet red flesh color; dark red color of the fruit flesh (darker red than the YY red color of ‘Angeleno Black Seeded’); Scr from ‘Dixielee’ and ‘Red-N-Sweet’; scr from ‘Angeleno Black Seeded’.	Lycopene
Wf	White flesh; (named white flesh by Robinson); Wf is epistatic to B (Y renamed B by Henderson); WfWf BB* or WfWf bb white fleshed; wfwf BB yellow fleshed; wfwf bb red fleshed; B from breeding line V.No.3 and b from V.No.1; flesh color segregated into 12 white, 3 yellow and 1 red in the F2.	None
y	yellow flesh; recessive to coral (light) red flesh (Y); y from ‘Golden Honey’; Y from ‘Angeleno’ (black seeded).	Citrulline
y-o	orange flesh; allelic to y; Y (red flesh) is dominant to y-o (orange flesh) and y (salmon yellow flesh); y-o (orange flesh) is dominant to y (yellow flesh); cc y-oy-o I-C I-C from ‘Tendersweet Orange Flesh’; cc yy I-C I-C from ‘Golden Honey’; cc YY i-C i-C from ‘Sweet Princess’.	Prolycopene