petals of snake gourd and its long serpent-like fruit, dangling beneath a garden arbour, make for a picturesque sight. The spiny fruit of teasel gourd and African horned melon and the explosive fruit of squirting and exploding cucumbers have brought these cucurbits into commercial trade as well. The most recent horticultural trend affecting cucurbits is the passion for succulents. Collectors are beginning to learn of and trade among themselves the caudiciform cucurbits of Africa (e.g. Gerrardanthus and Trochomeria), Madagascar (Seyrigia and Xerosicyos) and North America (Marah and Ibervillea).
COMMERCIAL PRODUCTION AREAS AND IMPORTANCE
According to the Food and Agriculture Organization (FAO) of the United Nations, watermelon is the most popular cucurbit in the world (Table 2.1). The FAO estimated that 3,477,000 ha of watermelon were harvest worldwide in 2014, producing 111,009,000 t of fruit. Next in total world production were cucumber, melon, and then squash and pumpkin. All of these crops have seen increases in production since the 1970s (Table 2.1). The greatest growth in harvested area (355%) was seen in pumpkins and squashes, but an approximate 200% increase was also seen for other cucurbit crops. In watermelon, production has increased by 444% over the past three decades. Cucumber production has seen a 343% increase in production over the same time period.
Table 2.1. Leading countries in the production of cucurbits.
China remains the leading producer of the major cucurbit crops in the world. Although China is also a prominent producer of luffa, wax gourd and other cucurbits of Asian origin, production statistics for these crops are not readily available. China exports various cucurbit products, including fresh fruit, watermelon and squash seeds, and dried fruit of the medicinal (and low-calorie sweetener) monk fruit or luo-han-guo (Fig. 2.2). In 1990, the Chinese Agricultural Department estimated that 30% of the land in China that was devoted to vegetable production was sown in cucurbits (Yang and Walters, 1992). In 2014, the second leading producer of watermelons and melons was Turkey. Russia was the second leading producer of cucumbers, and India was second for squash and pumpkins (Table 2.1).
Fig. 2.2. Luohan beverage mix from China. Seeds and fruit of luo-han-guo are pictured on the package.
It is very difficult to obtain reliable statistics on cucurbit production in many countries because governmental statistics are not readily available to the public and data gathering and reporting procedures vary from country to country. Also, different agencies report different statistics for the same country.
Besides the major crops, there are some minor cucurbit crops of international commercial importance. Already mentioned are the fruit of monk fruit (luo-han-guo) exported from China. China and Japan both export other cucurbits of medicinal interest, such as preparations of Gynostemma and Trichosanthes, which are finding their way into the American herbal medicine market. Medicinal preparations of colocynth have a long history of trade from African to European pharmacies. Fruit of African horned melon that are commercially produced in New Zealand appear in American and European food markets sporting the trade name ‘kiwano’. Because of expanding demand, Kenya and Israel have also become important exporters of this attractive fruit. Japan and Central America are the major exporters of luffa sponges. In the early 1940s, when luffa sponges were an important source of industrial filters, Brazil exported almost 2 million sponges per year to the USA alone. In 1985, Costa Rica was the leading exporter of chayote. In 2011, Mexico became the leading exporter of chayote to the USA with 19,500 t being exported, though Costa Rica’s production was similar. Both Costa Rica and Mexico still ship large amounts of chayote to other Latin American countries and to Europe. Decorated bottle gourds are a source of foreign currency in Peru. Snake gourd and bitter gourd (Fig. 2.3) are bottled or canned for export in Asia and have been for decades.
Fig. 2.3. Bitter gourd, immature fruit and canned. (Reprinted by permission from The New York Botanical Garden, © 1988, Economic Botany 42, 287, J. Ruh and J. Thieret, photographers, in Walters and Decker-Walters, 1988.)
Cucurbits are important in the international seed trade. In addition to the major food crops, seed companies offer germplasm of other edible and ornamental cucurbits such as luffa, wax gourd, bottle gourd, bitter gourd, stuffing cucumber and casabanana.
Many domesticated species can become troublesome weeds, particularly in agriculture and elsewhere. Feral populations of cucurbit crops occur along roadways, railroad tracks, stream banks, settlements and waste areas in the Americas, Europe, Africa, Asia, Australia and even islands in the Pacific. Particularly widespread and persistent are weedy forms of bitter gourd, watermelon, citron and species of Cucumis. Also common are escapes of species of Cucurbita and Luffa, ivy gourd, colocynth, bottle gourd, squirting cucumber and red hailstone (Thladiantha dubia).
Cotton fields in southern Asia and southeastern USA are plagued with weedy plants of Queen Anne’s pocket melon (Cucumis melo var. dudaim) and Texas gourd (Cucurbita pepo ssp. texana). The gourd problem has affected soybean and cotton production in Mississippi, Louisana, Arkansas and Texas.
West Indian gherkin (Cucumis anguria) is reportedly a pest in sugar cane and peanut fields in Australia. This species also grows wild in many areas of the New World, including Brazil and various Caribbean islands. It is not native to the New World; rather, it escaped from cultivation, apparently after being introduced with the African slave trade.
Commercial seed trade has been another disperser of weeds. During the 19th century, species of Old World bryony (Bryonia spp.) were sold in the USA as ornamentals and sometimes escaped. Similarly, wild cucumber (Echinocystis), a native of North America, has escaped from European gardens.
THE MECHANICS OF PLANT BREEDING
Manual pollination
Large unisexual flowers and sticky pollen facilitate manual pollination in cucurbit breeding experiments. In squash, male and female flowers to be used the next morning are chosen the previous day. The closed corolla of an appropriate squash flower will have a light touch of yellow at the apex. The corolla tips of the staminate flower may be slightly separated also (Fig. 3.1). The apices of the chosen flowers are taped, tied or covered to prevent pollinator entry. The next morning, a staminate flower is removed and opened and the
