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Genes for watermelon [Citrullus lanatus (Thunb.) Matsumura & Nakai] fruit traits have been identified since the 1930s. We conducted a study of fruit traits including fruit stripe width, stripe color, rind color, fruit shape, and blossom end shape (concave vs. convex). Ten watermelon cultivars (inbred lines) were used as parents. Several new genes or alleles were discovered. A series of alleles at the g locus is proposed to explain the inheritance of fruit rind pattern: G (medium or dark solid green), g (wide stripe), g (medium stripe), g (narrow stripe), and g (solid light green or gray). The dominance series is G > g > g > g > g. Another series of alleles at the ob locus is proposed for the fruit shape: allele Ob for elongate fruit, which is the most dominant; allele Ob (not the same as the o gene for round) for the round fruit; and allele ob for oblong fruit, which is the most recessive. Gene csm is proposed for the clear stripe margin in the cultivar RedN-Sweet and is recessive to the blurred stripe margin (Csm) in ‘Crimson Sweet’, ‘Allsweet’, and ‘Tendersweet Orange Flesh’. Watermelon [Citrullus lanatus (Thunb.) Matsumura & Nakai] is a major vegetable crop cultivated as an annual in warm regions worldwide.Watermelon accounts for 6.8% of vegetable production area around the world (Guner and Wehner, 2004). Harvested area decreased 15% from 2002 to 2012, but total production has remained constant around 2 million Mg. The watermelon industry has increased in value from $497 to $520 million from 2003 to 2012 in the United States (USDA, 2004, 2012). Watermelon has a small genome: 4.2 · 10 base pair for the 22-chromosome diploid (Arumuganathan and Earle, 1991). The watermelon genome has been sequenced and 23,440 predicted protein-coding genes were identified (Guo et al., 2013). Genetic studies since the 1930s have identified more than 100 genes. The genes control traits in seed and seedling, vine, flower, and fruit, as well as resistance to diseases, insects, and stress (Wehner, 2008a). The genes of watermelon have been described in several reviews (Guner and Wehner, 2004; Wehner, 2008a, 2012). The rind of watermelon fruit can be striped or solid colored. The solid rind patterns include solid dark green as in ‘Black Diamond’, solid medium green as in ‘Peacock Shipper’, solid light green as in ‘King&Queen’, gray (medium green reticulations on a light green background) as in ‘CharlestonGray’, or golden as in ‘Royal Golden’ (Guner and Wehner, 2003, 2004; Gusmini and Wehner, 2006a, 2006b). In some reports, gray rind has been described as yellowish white or yellowish green (Porter, 1937). The stripes of watermelon can be characterized by stripe width (narrow, medium, or wide), stripe color, and background color (dark green, medium green, or light green). Since the stripe patterns are alternating light and dark-colored stripes on the rind, there is ambiguity deciding which are the stripes. In this study, we considered the dark area to be the stripes. This follows the observation that the dark areas cover the vascular tissue below the fruit surface (Korn, 2007). Although the developmental basis of the longitudinal stripe pattern in watermelon has not been studied in detail, a clonal mosaic model was proposed based on observational evidence (Korn, 2007). In both young and mature fruit of ‘Ruby Red’, the vascular bundles run beneath the dark green reticular stripes, showing the association of the two. This association is also found on watermelon pedicels. Korn (2007) suggested that the vascular bundles are a prepattern determining the stripes on the fruit surface. The reticulations in the stripe composed of sets of polygons give the basis of the clonal mosaic model. This clonal mosaic model hypothesizes that a cell gives rise to a clone of various types of cells (the polygon) with dark green border, light green center, and medium green region between the two. This model explains the formation of the multiple-celled polygons that compose the darker green stripes with reticulations on the fruit of ‘Ruby Red’. Besides being striped or solid colored, there are additional modifications to watermelon rind, such as the netted reticulations within stripes or on the whole fruit surface, mottling (irregularly shaped light color) on the otherwise solid dark-colored background, ground spot color, furrowed fruit surface, and explosive rind. The reticulations are found on many cultivars, including some light green cultivars such as Charleston Gray, where the reticulations are more intensive near the surface of the vascular bundle and less intensive on the areas between vascular bundles. The reticulations are also found on the medium-green stripes of some striped cultivars, such as Ruby Red, China 23 (the typeline for the p gene) (Weetman, 1937), Crimson Sweet (the medium-width stripe cultivar in our experiment), and in the surrounding area of the ground spot of the otherwise solid dark green fruit such as ‘Black Diamond’. It is possible that the dark green cultivar Black Diamond is actually reticulated, but the reticulations are not visible due to the dark rind color. Consumers often express a preference for particular rind patterns. Striped rind pattern is usually preferred over other patterns such as gray. Resistance to bacterial fruit blotch was associated with cultivars having dark rather than light rind; however, the effect may have been a nongenetic association (Wehner, 2008b). Rind toughness is important for postharvest handling and shipping. Other external rind traits, such as furrowed fruit surface and different fruit shapes, also affect customer acceptance. Studies by Porter (1937) and Weetman (1937) identified three alleles at the g locus that produce solid dark green (G), striped (g), or gray (g) rind pattern. The gray rind pattern has been described as light green in some studies. Solid dark green (G) is dominant to striped (g) and gray (g). Striped rind pattern (g) is dominant to gray (g). The allele G is from ‘California Klondike’, g is from ‘Thurmond Gray’, and g is from ‘Golden Honey’. Recently, Kumar and Wehner (2011) found a second gene controlling the dark green rind vs. gray rind pattern. The g gene is considered g-1 and the second gene g-2, from type-line ‘Minilee’. The g-1 and g-2 genes produce the gray rind pattern. The others (G-1G-1G-2G-2, G-1G-1 g-2g-2, and g-1g-1 G-2G-2) produce dark green rind pattern. The gene ins from ‘Navajo Sweet’ (Ins from ‘Crimson Sweet’) produces intermittent stripes, starting with narrow dark green stripes at the peduncle end of the fruit and becoming irregular in the middle and nearly absent at the blossom end of the fruit (Gusmini and Wehner, 2006a). Very narrow stripe on a light background on the rind of ‘Japan 6’ is called pencilled (p) phenotype. It is recessive to the netted (medium green-colored network) (P) rind pattern of ‘China 23’ when disregarding the dark stripes on the light background (Weetman, 1937). Another rind gene described by Weetman (1937) is the m gene from ‘Long Iowa Belle’ for the particular randomly distributed and irregularly shaped greenish-white mottling pattern. The mottling pattern differs from the rest of the fruit not only in color but also in the character of the epidermis. This special phenotype was called the ‘Iowa Belle’ Received for publication 25 Jan. 2016. Accepted for publication 27 Mar. 2016. We gratefully acknowledge Tammy L. Ellington for assistance with the field tests and Laura Arellano for assistance with greenhouse pollinations. Corresponding author. E-mail: todd_wehner@ ncsu.edu. HORTSCIENCE VOL. 51(5) MAY 2016 487 phenotype by Weetman (1937). It was recessive to the nonmottling trait of ‘Japan 4’ and ‘China 23’ when disregarding the stripes on ‘China 23’ (Weetman, 1937). Since many of the type-lines used byWeetman (1937) are not available, it is not possible to study the p and m genes. ‘Moon and Stars’ has large yellow spots (moons) and small yellow spots (stars) over a dark green background, which occurs on the fruit rind as well as the foliage (cotyledons and true leaves). The trait is controlled by the gene (Sp), which is dominant to the uniform green color (sp) of ‘Allsweet’ (Poole, 1944; Rhodes, 1986). The gene Yb produces the yellow belly trait on the fruit of ‘Black Diamond Yellow Belly’. This cultivar has a dark yellow to orange-colored ground spot on a solid dark green fruit and is dominant to the usual creamy white ground spot (yb) of ‘Black Diamond’ (Gusmini and Wehner, 2006a). The golden gene go produces a golden yellow color of mature fruit as well as on the older leaves of ‘Royal Golden’. This gene is recessive to the normal green leaves and fruit (Go) of ‘NC 34-9-1’ and ‘NC 34-2-1’ (Barham, 1956; Robinson et al., 1976). Watermelon fruit with furrowed parallel indentations (f) was found to be recessive to the smooth surfaced fruit (F). Since type-lines were not given in the original reference, ‘Stone Mountain’ or ‘Black Diamond’ might be used for f, and ‘Mickylee’ for F (Poole, 1944; Wehner, 2008a). The gene e from ‘California Klondike’ produces an explosive rind that is tender and bursting when cut. It is recessive to tough rind (E) from ‘Thurmond Gray’ and ‘Golden Honey’ (Poole, 1944). The explosive trait was not correlated with fruit rind thickness, but with rind cell wall thickness (Kenny and Porter, 1941). Watermelon fruit shape can be elongate, oval, round, or oblong, based on the length to width ratio. Weetman (1937) investigated the inheritance of fruit shape in the families of ‘Long Iowa Belle’ (elongate fruit) · ‘Round Iowa Belle’ and ‘China 23’ (round fruit), as well as ‘Long Iowa Belle’ · ‘Japan 6’ and · ‘Japan 4’ (round fruit). He found that elongate fruit shape (OO) was incompletely dominant to round fruit shape (oo) with the heterozygote (Oo) being oval shaped (Weetman, 1937). Poole and Grimball (1945) found the same inheritance pattern in ‘Peerless’ · ‘Baby Delight’ and ‘Northern Sweet’ · ‘Dove’. The ob

Qualitative Inheritance of External Fruit Traits in Watermelon