Gone Global: Familiar and Exotic Cucurbits Have Asian Origins

Cucurbits comprise the highly diverse family known as Cucurbitaceae that includes cultivated, feral, and wild species (Robinson and Decker-Walters, 1997). Many of the cultivated species such as squash (Cucurbita ssp.), watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai], cucumber (Cucumis sativus L.), and melon (Cucumis melo L.) are familiar to U.S. and world markets. Others such as bitter gourd (Momordica charantia L.) are less familiar in the United States. Cucurbits are cultivated more broadly than any other vegetable species after tomato, Solanum lycopersicum L. (). Cucurbits exhibit great genetic diversity expressed phenotypically in vegetative, e.g., plant architecture and growth habit, floral, e.g., sex expression, and fruit characters that include size, shape, skin texture, exterior and interior colors, sweetness and flavor, and postharvest shelf life. They are especially known for their fruit, which may be consumed fresh, cooked or baked, dried, or processed (Robinson and Decker-Walters, 1997). Immature or mature fruit are, depending on the species, consumed as fresh or cooked vegetables. Melon and watermelon are especially well known for their sweet, flavorful, and colorful fruit that are usually eaten fresh but may be processed in confections or jams (Fig. 1). Cucurbit seeds are edible fresh (Anon., 2012c) or dried (Fig. 1). They are a source of high-quality vegetable oil (Fig. 1) and the expressed meal is high in edible protein (Jacks et al., 1972). Roots (Gathman and Bemis, 1990) and leaves (Jensen, 2012) of some species may also be used for industrial or culinary purposes. Asia and cucurbits are intertwined. Origins of the many members of the Cucurbitaceae have been of great interest for 100+ years, some regarded as Old World (Asia and Africa), whereas others are regarded as New World (the Americas) species (for a somewhat dated overview, see Esquinas-Alcazar and Gulick, 1983). Recent analyses indicate, however, an Asian origin of the family Cucurbitaceae and numerous oversea dispersal events (Schaefer et al., 2009). India and Southeast Asia, including China, comprise the primary and secondary centers of diversity, respectively, of cucumber. India and central and southwest Asia comprise the primary center of diversity for melon with China as a secondary center of diversity (Esquinas-Alcazar and Gulick, 1983). India and Africa are primary centers of watermelon and related species (Esquinas-Alcazar and Gulick, 1983). Melon and cucumber likely moved westward overland through central Asian trade routes, collectively referred to as the Silk Road (Wild, 1992) through central Asia and the Middle East to Europe and Africa and from there onto the New World. In contrast, the center of diversity for watermelon is in Africa (Esquinas-Alcazar and Gulick, 1983); it is thought that cultivated watermelon moved from there to Asia. The center of diversity of bitter gourd is the Old World tropics with its highest diversity in India, China, and Southeast Asia (EsquinasAlcazar and Gulick, 1983). Bitter gourd likely arrived in the United States with Chinese immigrants in the 18th century. Seedless (tetraploid) watermelon, the product of an early 20th century discovery in Japan, entered the U.S. marketplace at the end of that century, where it quickly gained popularity when bred into a small fruit size background and adapted to U.S. growing conditions. Grafting of watermelon onto disease-resistant rootstocks was developed during the 1920s in Japan and Korea (Davis et al., 2008). This technology holds great promise for melon and watermelon production in the United States as the use of methyl bromide and other soil fumigants become more restricted (Davis et al., 2008). New resources, i.e., crop germplasm, and technology, e.g., tetraploidy and grafting, contribute to sustainable crop productivity (Day, 1997). We provide an overview of the positive impact of Asian cucurbit germplasm and technology on U.S. melon, cucumber, and watermelon production and the potential for bitter gourd, a relatively new commercial crop in the United States with many useful attributes.