are common in the greenhouse trellis type, the Middle Eastern greenhouse (Beit Alpha) type and, more recently, field slicers and field pickles. Parthenocarpic pickling type has become popular in northern Europe and most of the USA, due to seedless fruit and higher yield. Field production of parthenocarpic cultivars depends on isolation from conventional cultivars having staminate flowers, as well as the exclusion of beehives from the area.
Anderson (1894) determined that a developing squash fruit gained weight at an average rate of 1 g per minute. The greatest weight increase was at night. The growth rate for cucurbit fruit is influenced by exogenous conditions (e.g. higher temperatures and greater light exposure increase the growth rate) as well as by endogenous plant conditions, such as the presence of other developing fruit, which retards growth.
Several studies on the inheritance and development of fruit shape in squash (C. pepo) were conducted by Sinnott (1932). He reported that fruit shape is evident in the shape of the immature ovary, with ultimate shape affected by both genetic and environmental factors. Also, fruit that are set first may be shaped differently than those set later, the difference being evident in the shape of the ovaries.
Immature ovaries are usually green, although those of squash cultivars with gene B may be yellow. Fruit of various cucurbits, including luffa and bottle gourd, remain green until fruit senescence, at which time they turn tan or brown. Other cucurbits develop rind coloration changes during maturation. In these, chlorophyll depletion reveals the presence of additional pigments after pollination. For example, the green fruit of many squash cultivars become yellow or orange as they age. Colour changes usually begin at the blossom end of the fruit. In most wild and cultivated Cucurbita, rind patterns, such as stripes or mottling, are lightly visible on the ovary, becoming more distinct soon after pollination. However, the white fruit of ‘Mandan’ (C. pepo) reach almost full size before the dark green markings appear. Fruit markings persist at maturity for some squash cultivars, but fade away in senescent fruit of others.
In young melon fruit of the Cantalupensis Group of cultivars, rapidly dividing cork cells develop below the epicarp. Near maturity, this growth breaks through to form a network of grey corky tissue covering the rind, as is evident in the netting of muskmelon cultivars.
A unique case of adaptation to a particular ecological niche is exemplified by Cucumis humifructus Stent. This African species has a geocarpic fruit, similar to that of peanut. After flowering and setting fruit above ground, similar to other Cucumis species, the developing fruit is thrust downward and completes its development several inches below the soil surface. In its native land, the African anteater or aardvark (Orycteropus afer) consumes the subterranean fruit. It is a symbiotic relationship, with the aardvark using the fruit as a source of food and water in the arid area where the plant often grows, and providing a means of seed dispersal for the plant. C. humifructus is called aardvark cucumber because of this relationship, but it is more closely related to melon than to cucumber.
‘Cucurbits are weeds waiting to become crops.’ While this anthropomorphic statement may be an over-simplification of crop evolution in the Cucurbitaceae, supporting evidence can be seen in the vast array of valuable plant products found within the family. Aboriginal plant gatherers were probably attracted to some of these products, particularly the relatively large, long-keeping and sometimes showy fruit. After fruit were taken back to camp, seeds that were purposely discarded, accidentally dropped or partially digested found new life on rubbish heaps, settlement edges or other disturbed areas near camp. Eventual recognition of the value of the resident cucurbits led to their appreciation, horticultural care and further exploitation. Finally, seeds and, more rarely, vegetative propagules were carried by and exchanged among migrating bands of these incipient cultivators, gradually turning the earliest cultivated cucurbits into domesticated crops.
It was not only because cucurbits were wanted by human gatherers that they became domesticated. Certain physiological and genetic characteristics generally associated with weeds, or colonizing species, allowed cucurbits to adapt to human habitats. Fast, indeterminate growth, developmental plasticity in response to environmental conditions (especially regarding sex expression) and genetic diversity at the genomic, chromosomal and gene levels enabled these cucurbits to continue their survival through the coevolutionary relationship that humans call domestication. In turn, this relationship brought many changes to domesticated cucurbits: the size of various plant parts increased; early female flower production was selected; seed dormancy was reduced; photoperiod response was eliminated; fruit bitterness was eliminated; and fruit flavour and appearance were improved.
Given the nature of cucurbits, it is not surprising that they are among the most ancient of cultivated plants. Archaeological evidence suggests a pantropical distribution for bottle gourd going back more than 10,000 years. Bottle gourd may have been cultivated in Asia, Africa and the New World at that time, or later if the oldest remains are of wild plants. Using molecular taxonomy, even older times can be seen, although humans did not exist then. Evidence of human use of cucurbits in the form of seeds or fruit rinds of Cucurbita pepo has been found at sites dating ca 10,000 bp in Mexico and ca 5000 bp in central USA (Smith, 1997a, 2006). Phytoliths are particles of silicon dioxide found in the cells of Cucurbita spp. These particles remain in soil samples and can be used as a diagnostic tool in archaeological studies of this genus. This technique has been used to document the presence of domesticated Cucurbita spp. in South America as early as 12,000 bp (Piperno and Stothert, 2003). Enlarged fruit parts indicate that other squash species were being cultivated for food in the New World by 7000 bp, if not earlier.
Cucumber (Cucumis sativus) is of Asiatic origin, with its primary centre of diversity in India and secondary in China. Although cucumber evolved from melon, the two species cannot be crossed. Cucumber can be crossed with Cucumis sativus var. hardwickii, C. s. var. sikkimensis and C. s. xishuangbannanensis. Also, Cucumis hystrix, a wild species with traits from both melon and cucumber, has been crossed successfully with cucumber. However, Cucumis setosus is a melon relative that looks like cucumber, but will not cross with it. Cucumber has been grown in Asia for several thousand years. The remains of Cucumis crops (melon or cucumber) in eastern Iran have been dated to the third millennium bc.
Melon (Cucumis melo) likely originated in India from C. trigonus or C. callosus (Sebastian et al., 2010). The Australian species C. picrocarpus has the highest DNA sequence similarity to C. melo. However, the oldest wild relatives of melon, such as C. hirsutus, C. humifructus and C. sagittatus, originated in Africa. Melon was grown in Egypt in the second millennium bc and in Iran during the third millennium bc. Humans moved the melon throughout the Middle East and Asia, making it an important vegetable in India, Egypt, Iran and China. Iran, Afghanistan and China are secondary centres of melon diversification. Spain is a tertiary centre of diversity.
Melon was one of the most important vegetables in ancient China, with archaeological remains there dating back to 5000 bp. The origin and domestication of melon is still debated, though evidence for two lineages have been described, with an Indian relative (C. trigonus) being the most closely related living relative to C. melo (Endl et al.,
