by Todd C. Wehner
Department of Horticultural Science
North Carolina State University
Raleigh, NC 27695-7609
Watermelon varieties have been described in the vegetable variety lists maintained by the American Society for Horticultural Science. Also, a complete set of descriptions for all vegetable crops from lists 1 through 25 has been collected into a book to be produced by ASHS Press. Seeds are available for many of the open pollinated and inbred varieties on the list, but there are a significant number of varieties that are no longer available. Watermelon breeders should obtain and evaluate a sample of the varieties available to become familiar with the diversity of germplasm. It is also useful to observe the improvement in horticultural traits that has been made in varieties developed over time.
A breeding program usually is started by intercrossing the best varieties currently available, or by crossing the best varieties with accessions having one or more useful traits missing from the elite varieties. Thus, in the beginning a watermelon breeder will need to obtain seeds of the best varieties, a set of varieties developed at different times in the past, a set of accessions from germplasm repositories, and lines with useful or interesting gene mutants.
A survey of popular varieties in the ten major watermelon-producing states in the United States by D.N. Maynard in 2000 indicated that popular varieties for commercial production were almost all hybrids, with few open-pollinated varieties being used commercially. Popular diploid (seeded) open-pollinated varieties (‘Allsweet’, ‘Black Diamond’, ‘Calsweet’, ‘Crimson Sweet’, ‘Jubilee II’, and ‘Legacy’) were grown mostly in one state each, suggesting regional adaptation or local demand. Hybrids generally were grown in several states, suggesting they have wider adaptation. The ‘Allsweet’ type, generally considered to be of high quality, was represented by more than half of the listed varieties (three of the open-pollinated and 11 of the hybrids). The most popular diploid (seeded) varieties were ‘Sangria’ and ‘Royal Sweet’ (seven states), ‘Fiesta’ (six states), and ‘Mardi Gras’ and ‘Regency’ (five states). For triploid (seedless) varieties, almost half of the varieties were ‘Tri-X-313’ type. The most popular triploid varieties were ‘Tri-X-313’ (ten states), ‘Summer Sweet 5244’ (nine states), ‘Millionaire’ (eight states), ‘Genesis’ (five states), and ‘Tri-X-Shadow’ (four states).
In order to develop improved varieties for an industry in a particular region of the world, the watermelon breeder will need to have seeds of varieties, breeding lines, populations, plant introduction accessions, and gene mutants that express the traits of interest at a high level. The breeder should identify a source that has the highest level of expression. That would be true whether the trait is quantitatively inherited (fruit yield, earliness, size, sweetness) or qualitatively inherited (dwarfness, anthracnose resistance, flesh color). If there is a choice of accession for a particular trait (for example, white flesh), it is better to use an adapted accession with the best genetic background. Thus, ‘Cream of Saskatchewan’ would be a better choice to use in the development of white flesh varieties for use in the United States, than a wild-type, white-fleshed citron having large vines, late maturity, hard flesh, bitter flavor, large green seeds, and seed dormancy.