Watermelon Breeding

North Carolina State University has had a breeding program on watermelon (Citrullus lanatus) for decades.

Warren Barham was the first watermelon breeder, starting around 1953. He worked with pathologist Nash Winstead, who went into administration in 1961. One of Dr. Barham’s graduate students was Tom Konsler, who later became a faculty member in the department. In 1958, Dr. Barham left to work as an onion breeder for Basic Vegetable, Inc, a vegetable dehydration company in Vacaville, CA (then Texas A&M Univ., then Barham Seeds). Warren Henderson took over the program in 1959. He worked with pathologist Sam Jenkins (1961-1986). Dr. Henderson retired in 1992, and Todd Wehner took over in 1993. The other U.S. public watermelon breeding program is located at Texas A&M University.

The objectives of the program are to expand our knowledge of watermelon genetics and breeding, educate graduate students interested in vegetable breeding, do research on problems affecting the watermelon industry, and develop improved cultivars and breeding lines for use in North Carolina and the U.S.

Watermelon, Citrullus lanatus (syn. C. vulgaris Schrad.) is an important crop in China, Africa, India, USA and other areas with a long, warm growing season. The plants are fairly drought resistant, flourishing on fertile, sandy soils in hot, sunny, dry environments. Worldwide consumption of watermelon fruit and their seeds is greater than that of any other cucurbit.

  • Introduction
  • NC State Breeding Program Overview
  • History of Watermelon
    • All Citrullus species originated in Africa, but C. colocynthis also grows wild in India. Citron (C. amarus) originated in southern and central Africa, sweet watermelon in northeast Africa, and egusi watermelon in west Africa. Sweet watermelon grows wild in Sudan, as well as Egypt, Ethiopia and Kenya, and may have evolved from C. rehmii or C. colocynthis.
    • Watermelon has a long history of cultivation in Africa and the Middle East. It has been an important vegetable in Egypt for at least 4000 years. By the tenth century ad, the crop was grown in China and southern Russia. Commercial production of black watermelon seeds has been ongoing in northwestern China for over 200 years. Watermelon was introduced to the New World by the Spanish in the sixteenth century, and quickly became popular with Native Americans. In the USA, it is commercially grown primarily in Florida, Georgia, California, Texas, North Carolina, South Carolina and Indiana.
  • Taxonomy
    • Seven species of Citrullus are currently recognized. C. lanatus subsp. vulgaris (Renner) is the sweet watermelon. The closely related egusi watermelon is C. mucosospermus (Vavilov). C. amarus Chomicki (formerly C. lanatus var. citroides) is the citron, tsamma or preserving melon. Another closely related species is C. ecirrhosus Cogn., the tendril-less melon. More distantly related (in order) species are C. rehmii De Winter, C. colocynthis and C. naudinianus. Three of the Citrullus species, C. ecirrhosus, C. rehmii, and C. naudinianis, are not cultivated. All species in the genus are cross-compatible with each other to varying degrees. Citrullus lanatus and C. ecirrhosus are more closely related to each other than either is to the colocynth, C. colocynthis (Navot and Zamir, 1987). Related genera (in order) include LagenariaBenincasa (Praecitrullus), Acanthosicyos, and Cucumis.
    • Sweet watermelon and egusi watermelon have been crossed to obtain traits from egusi, with success being higher when sweet watermelon was used as the female parent. Crosses of citron and sweet watermelon have produced progenies having preferential segregation (and reduced pollen fertility), making it difficult, although not impossible, obtain new (non-parental) combinations in plant breeding programs.
    • Citron (Citrullus amarus)
      • The fruit rind of preserving melon or citron (C. amarus, formerly C. lanatus var. citroides) is used to make pickles or conserves, and the fruit are fed to livestock (Fig. 4.7). Citron has white or pale green flesh that is bland to bitter. The large seeds are of various colours, including light green (e.g. ‘Colorado Preserving Melon’). In commercial production, over 100 fruit per plant and up to 200 seeds per fruit give seed yields of 500–700 kg ha−1.
      • Citron grows wild in Africa and as an escape elsewhere. It is a weed in watermelon growing areas of North America, causing severe problems in cotton and sorghum fields in Texas, where three distinct citron types exist. Citron crosses readily with watermelon, so seed production fields should be isolated and monitored. Citron fruit image (JPEG).
    • Egusi Watermelon (Citrullus mucosospermus)
      • Egusi watermelon (Citrullus mucosospermus Vavilov) is the most closely related species to sweet watermelon. Egusi watermelons, indigenous to western Africa, are usually spherical with bitter flesh, and have a soft, mucilaginous seed coat. They are cultivated for the consumption of their seeds, which vary widely in size and shape. Egusi seed image (JPEG).
    • Colocynth (Citrullus colocynthis)
      • The perennial C. colocynthis is cultivated for ‘colocynth’, a drug produced from the dried pulp of unripe but mature-sized fruit. Although colocynth fruit have bitter, white flesh, the non-bitter seeds are eaten and used for cooking oil in Africa. This species grows wild in northern Africa and southwestern Asia, and exists as an escape from cultivation in other areas, including Australia and southern Europe. Colocynth fruit image (JPEG).
  • Biogeography and Origin
  • Watermelon Uses
    • Watermelon fruit make a delicious and refreshing dessert, especially esteemed in hot weather. For centuries, watermelon and relatives such as citron have served as an important source of water in the Kalahari Desert and other arid areas of Africa. Watermelons are mostly eaten fresh, but in Africa they are also cooked. The rind may be pickled or candied. In the southern states of the former USSR, juice from watermelon fruit is made into a fermented drink or is boiled down to a heavy, sweet syrup.
    • Watermelon seeds are powdered and baked like bread in India. Roasted seeds are eaten in the Orient and the Middle East. Some Chinese cultivars used for this purpose have been bred to have very large seeds. However, big seeds can be objectionable for watermelons eaten as a dessert, and Japanese breeders have selected for small seed size.
    • Fresh
    • Fresh-cut slices and cubes
    • Juice
    • Rind Pickles
    • Candy (Glace’)
  • Production
  • Breeding
    • Commercial Breeding
    • Breeding Methods
    • Horticultural Traits and Breeding Objectives
    • Cultivar Types
    • Watermelon Cultivar List
      1. A-L
      2. M-Z
    • History, Important Varieties
    • Cultivar List
    • NC State Germplasm Releases
    • Germplasm Resources
      • Germplasm Exploration, Evaluation
      • Egusi watermelon
      • Similar to cucumber, watermelon has low diversity as a result of its narrow genetic base. This lack of diversity in general is in contrast to the large morphological variation observed in flesh color, seed size and color, and fruit rind pattern (discussed in detail in the above section). Watermelon, which originated in Africa at least 4000 years ago, was domesticated as a source of nutrients (seeds and flesh) and water in semi- and arid climates. From Africa or India (a secondary center of diversity), dessert watermelon was brought to the Mediterranean 800 years ago, and from there watermelon was developed to a higher degree of fruit quality. From its birth in the Mediterranean, sweet watermelon spread to Europe and China (secondary center of diversity) through the Silk Road. The tertiary center of diversity is central Asia.
    • Taxonomy, Morphology, Physiology
    • Flowering and Pollination
    • Genetics
      • Two genes of watermelon have been reported to govern anthracnose resistance, Ar-1 for race 1 and Ar-2-1 for race 2 resistance. Alleles db and Fo-1 provide resistance to gummy stem blight and race 1 of Fusarium wilt, respectively. However, gummy stem blight resistance appears to be due to more than just a single gene. Susceptibility to powdery mildew is governed by pm. Resistance to Papaya ringspot virus-watermelon strain controlled by a single recessive gene, prv. A moderate level of resistance to Zucchini yellow mosaic virus was conferred by a single recessive gene zym-FL. A high level of resistance to Zucchini yellow mosaic virus-Florida strain was controlled by a single recessive gene, zym-FL-2; not the same as zym-FL. Resistance to the China strain of Zucchini yellow mosaic virus was controlled by a single recessive gene zym-CH. A single dominant allele, Zym, confers resistance to zucchini yellow mosaic virus. Insect resistance genes for watermelon include Af (red pumpkin beetle resistance) and Fwr (fruit fly resistance).
      • Watermelon plants with short vines can be bred if they are homozygous recessive at the dw-2 locus or for one of the two alleles for dwarf plant habit at the dw-1 locus. Both genes make a super dwarf that has been used to develop cultivars for patio and container production. Branching at the lower nodes of the main stem is reduced by allele bl.
      • Andromonoecy is recessive to monoecy and conditioned by gene a. Two alleles are known that produce male sterility, ms and gms, the latter associated with glabrous foliage.
      • When plants are homozygous recessive for the e (explosive rind) allele, the fruit is tender (not tough rind, but can be thin or thick rind), bursting when cut. The f gene determines furrowed fruit surface. The incompletely dominant allele O governs elongate (OO), oval (Oo) and spherical (oo) fruit shape.
      • Dark green skin color (G-1 and G-2) is dominant, and other alleles at the g-1 locus determine the degree of color and striping: G (medium or dark solid green); gW (wide stripe); gM (medium stripe); gN (narrow stripe); and g (solid light green or gray). The dominance series is G > gW > gM > gN > g. Greenish mottling of the exocarp is produced by the m allele, and pencilled lines by p. Golden mature fruit color and chlorosis of older leaves is governed by gene go. Rind pattern image (JPEG).
      • A gene with a dominant allele for white flesh (Wf) is epistatic to a gene for yellow flesh; the double recessive is red-fleshed. Allele C produces canary yellow flesh colour. The darkness of red colour in the flesh (and the amount of lycopene) is controlled by multiple alleles at the y locus. Scarlet red flesh (YScr) is dominant to coral red flesh (YCrl), orange flesh (yO) and salmon yellow flesh (y). The dominance series is YScr > YCrl > yO > y. The allele YScr is from ‘Dixielee’ and ‘Red-N-Sweet’; the allele YCrl is from ‘Angeleno’ (black seeded); the allele yO is from ‘Tendersweet Orange Flesh’; and the allele y is from ‘Golden Honey’. The su allele suppresses fruit bitterness. Flesh color image (JPEG).
      • The interaction of alleles at several genes, including d (dotted seed coat), r (red), t (tan) and w (white seed coat), determine seed coat colour and pattern. Clump is RR TT ww; tan is RR tt WW; white is RR tt ww; green is rr TT WW; red is rr tt WW; and white with pink tip is rr tt ww. Seed size is controlled by several genes, including l (long) and s (short seed) genes with s epistatic to l, and long recessive to medium or short. The phenotypes are LL SS for medium, ll SS for long, and LL ss or ll ss for short seed. The sources for genotypes are ll SS from ‘Peerless’, LL SS from ‘Klondike’, and LL ss from ‘Baby Delight’. A third gene, ts, produces tomato seed size that is smaller than short seed. Also, tiny seed (Ti, dominant to short seed) from ‘Sweet Princess’ produces seeds that are in between short and tomato seed. Five genes for seed protein composition (Spr-1, Spr-2, Spr-3, Spr-4 and Spr-5) are included in the watermelon gene list. Seed size image (JPEG).
      • The Citrullus genome has been sequenced using the Chinese breeding line 97103, and ‘Charleston Gray’. According to studies of synteny, the 11 chromosome pairs of watermelon evolved into 12 chromosome pairs in melon which then evolved into 7 chromosome pairs in cucumber.
      • Genes of watermelon
    • Disease, Insect, and Stress Resistance
      • Chilling Resistance Induced by Hormones
      • Gummy Stem Blight (Overview)
      • Gummy stem blight screening
      • Powdery Mildew
      • Virus (PRSV-W, WMV, ZYMV)
      • Transplant Protection Using Hormones
      • Drought Resistance
        • Wild species of Citrullus demonstrated enhanced drought tolerance and produced elevated levels of citrulline.  A test of drought tolerance at the seedling stage revealed 25 Citrullus lanatus accessions from Africa with high tolerance amongst 1066 germplasm and breeding lines assayed. Many of these accessions were from Zimbabwe, with an equal split between domestic (Citrullus lanatus) and wild (Citrullus amarus) types.  These have potential for use as breeding parents to create both cultivars and rootstock lines with enhanced drought tolerance. In Turkey, 85 watermelon accessions were screened for drought tolerance in field experiments with deficit irrigation. Over a third demonstrated drought tolerance based on 9 trait measurements, with one accession rating 99 on a scale of 0 to 100.  These drought tolerant genotypes are serving as the basis for development of new watermelon cultivars adapted to deficit irrigation and periodic drought conditions.  The shift to smaller fruit size in commercial watermelon markets may complement enhanced drought tolerance traits if there is reduced water demand from small fruit.
  • Biotechnology
  • Production
    • Cultural Practices
    • Seeding
    • Transplanting and Rootstocks
    • Growth Stages
    • Greenhouse Production
    • Weeds and Mulch
    • Irrigation and Fertilizer
    • Pest Management
    • Harvesting and Postharvest Physiology
    • Pest Management
  • Marketing
  • Production Costs
  • Consumption
  • Nutritional Composition
  • Seed Production and Sources
  • Wehner Publications
  • Extension Publications
  • Watermelon Publications