Cucurbits. James R. Myers
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by individual treatment of each small area of a farmer’s field, study of the microenvironment, and the concept of stability of performance for cultivars. In research, we must now account for a greater number of the variables present in any biological experiment.
Research on cucurbits around the world has greatly increased our knowledge of this crop group. We could not begin to cover all the pertinent information in one text. Instead, we hope that this book will give the reader a general awareness of cucurbit crop production, an understanding of the underlying biological concepts as they pertain to cucurbits, and a jumping-off point from which to pursue investigations on particular crop species.
Although diverse, most cucurbits do share a collection of characteristics (e.g. rapidly growing vines with tendrils, possessing relatively large fruit, adaptable to the point of becoming weeds, containing various bioactive compounds) that make them a unique, fascinating, and useful family of plants. Continued research should lead to their enhanced exploitation and appreciation.
We would like to thank the previous authors of this book, R.W. Robinson and D.S. Decker-Walters, who formed the foundation on which we built this version. We would also like to thank Liberty Hyde Bailey, Tom Whitaker, Henry Munger, Clint Peterson, Carroll Barnes, Greg Tolla, Fred Andrus, Jim Crall, Gary Elmstrom, Don Maynard, Tom Williams, Linda Wessel-Beaver, Jim McCreight, Harry Paris, Brent Loy, V.S. Sheshadri, Tom Zitter and Michel Pitrat, who did so much to increase our knowledge and appreciation of cucurbits.
The Cucurbitaceae is a family of frost-sensitive and predominantly tendril-bearing vining plants that are found in subtropical and tropical regions around the globe. There are only a few species that are native to temperate climates; they are either prolific seed-producing annuals, perennials that live for one season until killed by frost, or xerophytic perennials whose succulent underground parts survive the winter. Ecologically, the family is dichotomous; many genera flourish in the humid tropics, particularly in southeastern Asia and the neotropics, whereas other genera are native to the arid regions of Africa, Madagascar and North America. Members of the latter group, the xerophytes, usually have large perennial roots and succulent stems that are clambering and creeping and at least partially subterranean; in some cases, tendrils or leaves are lacking or greatly modified.
Although most crops in the Cucurbitaceae have been selected from the mesophytic annuals, concern over famine and fuel sources in arid countries has led to interest in turning some of the xerophytes into agricultural crops.
‘Cucurbits’ is a term coined by Liberty Hyde Bailey for cultivated species of the family Cucurbitaceae. Beginning in the early 20th century, the term has been used not only for cultivated forms, but also for any species of the Cucurbitaceae, and it will be so used in this book.
Other vernaculars applied to the family and various of its members are ‘gourd’, ‘melon’, ‘cucumber’, ‘squash’ and ‘pumpkin’. Of these, squash and pumpkin are the most straightforward, almost always referring to species of Cucurbita. An exception is the fluted pumpkin, which is Telfairia occidentalis. The unqualified terms melon and cucumber usually define Cucumis melo and Cucumis sativus, respectively. However, confusion develops when modifiers are added to these terms. Whereas muskmelon or sprite melon refers to a specific type of C. melo, watermelon is Citrullus lanatus, wintermelon is Benincasa hispida and bitter melon is Momordica charantia. Gourd generally is used to describe a cucurbit fruit with a hard, durable rind; usually it refers to bottle gourd (Lagenaria siceraria), or a wild species of Cucurbita, or an ornamental form of Cucurbita pepo. However, various other cucurbits also are called gourds, such as luffa sponge gourd (Luffa aegyptiaca), ridge gourd (Luffa acutangula) and some that do not have hard rinds, such as bitter gourd or bitter melon (M. charantia) and ivy gourd (Coccinia grandis). Sometimes the term refers to tough-rinded species of other plant families, such as the tree gourd (Crescentia cujete L., Bignoniaceae).
Complicating matters further, more than one common name is often applied to a single species. For example, names for B. hispida include ash gourd, white pumpkin, wax gourd and winter melon. Sometimes different names refer to distinct crops within a species, such as pumpkin, zucchini and acorn squash in Cucurbita pepo. In other cases, the different common names for the same species are used interchangeably. Frequently used common names for cucurbit crops are given in the Appendix.
Popular terms for the cucurbits may be confused in other languages as well. Cucumber and melon are sometimes considered the same in India. Older terminology in Chinese included ‘guo-kua’, which is translated into English as ‘melon’, but it includes watermelon (C. lanatus) as well as melon (C. melo). Also, ‘tsaikua’, which usually translates as ‘gourd’, refers to B. hispida, C. sativus, M. charantia and species of Cucurbita and Luffa. This is no longer a problem in China, since the names in Mandarin are now precise.
The family Cucurbitaceae, which is not closely related to any other plant family, consists of two well-defined subfamilies, eight tribes (representing varying degrees of circumscriptive cohesiveness) and about 118 genera and 825 species (Jeffrey, 1990). The four major cucurbit crops (watermelon, cucumber, melon, squash) and five other important crops (luffa, bottle gourd, chayote, wax gourd, bitter gourd) in the family belong to the Cucurbitoideae subfamily. Four of these – watermelon, luffa, bottle gourd and wax gourd – belong to the tribe Benincaseae. The classification of these and other cultivated species is given in Table 1.1. Many more wild taxa have actual or potential economic value, making Cucurbitaceae one of the most important plant families for human exploitation.
Table 1.1. Taxonomy of cultivated cucurbit species.
Taxonomic studies of cucurbits at all hierarchical levels have been done. They include comparative analyses of morphology (including specialized studies on trichomes, stomata, palynology and seed coat anatomy), cytology, DNA, isozymes, flavonoids, cucurbitacins, amino acids and fatty acids in seeds, biogeography and coevolving insects. A monograph has been written on Cucumis (Kirkbride, 1993), and the taxonomic relationships within the Cucurbitaceae are being improved using molecular markers (Schaefer et al., 2009; Chomicki and Renner, 2014). These new studies have been useful to the areas of crop improvement and germplasm conservation.
Seedlings
Most cucurbit seedlings are epigean, germinating with the tips of the cotyledons initially