Cucurbita argyrosperma

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Botanical name: Cucurbita argyrosperma Huber
Family: Cucurbitaceae
Common names. English: cushaw (United States); Spanish: calabaza, calabaza pinta, calabaza pipiana (Mexico), pipián (Mexico, El Salvador, Nicaragua, Costa Rica), saquil, pipitoria (Guatemala)

Origin, domestication and expansion

Cucurbita argyrosperma is one of the cultivated species of the genus which has undergone the most profound study in recent years. There are two subspecies: i) argyrosperma, comprising four varieties argyrosperma callicarpa. stenosperma and palmieri - three of which include all the cultivated types, while the fourth corresponds to spontaneous populations of northeastern Mexico that are generally known as Cucurbita palmieri L. Bailey; ii) sororia which includes wild populations with a wide distribution from Mexico to Nicaragua, originally described under the name C. sororia L. Bailey. This subspecies has been designated as the wild ancestor of the group.

According to the age of the archaeological remains discovered thus far, it has been suggest ed that domestication of C. argyrosperma must have occurred in southern Mexico more than 7 000 years ago.

The characteristics that were most transformed in the process of domestication of the ssp. argyrosperma were, as in other crops, mainly those connected with handling and preferred uses. For example, relatively uniform germination; a reduction in size and abundance of trichomes; an increase in the size of parts and organs used, such as fruits and seeds; and a reduction in the bitter taste of the flesh. It is considered that var. argyrosperma is the least specialized or most primitive of the group and that var. callicarpa, on the other hand, is the most recent or specialized.

The different degrees of variation in the nutritionally important parts of the three cultivated varieties of the complex argyrosperma suggest a strong association with human interests. The relatively large seed size of the var. argyrosperma indicates that it was mainly selected to obtain seeds, while the great diversity of shapes, colours and size of the fruits and seeds of var. stenosperma and callicarpa indicate that selection had a double aim: to obtain flesh as well as seeds.

Unlike with the rest of the cultivated species of Cucurbita, data on the distribution of cultivated Cucurbita argyrosperma varieties outside America are very scarce and there is no certainty that this species was cultivated at any time in the Old World or even outside its general area of domestication.

In South America, it is grown in Peru and Argentina, although it appears to involve very recent introductions of certain cultivars which can be classified within the var. callicarpa. In the United States, some cultivars of var. callicarpa are cultivated on a very low scale for nutritional purposes, and one cultivar of var. argyrosperma, Silver Seed Gourd, is occasionally grown as a horticultural curiosity.

The reasons for the sparse world distribution of this species are not known; although the situation is not surprising, given the low quality of the fruit's flesh compared with that of C. moschata or C. pepo and the size of the seeds of all the cultivated varieties that may have been attractive to the first Europeans who learned of them.

Uses and nutritional value

Throughout its distribution area, the flowers, young stems, young fruit and ripe fruit of C. argyrosperma are eaten as vegetables. The ripe fruit is occasionally used to prepare sweets although it is used most frequently as feed for livestock and poultry. The seeds are eaten whole, roasted, toasted or ground and are the main ingredient of sauces used to prepare various stews (for example, pipián -meat cooked in thick chili sauce, mole verde - a stew prepared with chili and green tomatoes). The seeds are the most important product, chiefly because of their oil (39 percent) and protein content (44 percent), and their consumption in urban areas of Mexico and other countries of Central America is fairly common.

In some regions of Mexico, the seeds and also the unripe fruit of wild taxa are used as food. The latter are eaten after being washed and boiled several times to rid them of the bitter taste deriving from the cucurbitins present in the flesh and placentae, while the seeds are simply washed, seasoned with salt and roasted or toasted. On the Yucatan peninsula, peasants use the flesh of the cultivated varieties' fruit to treat burns, sores and skin eruptions, while the seeds are prepared with water and used as an anaesthetic and to stimulate women's milk production for breastfeeding.

Botanical description

C. argyrosperma is a creeping or climbing monoecious plant, ranging from villous to pubescent and which may be hirsute, with short, rigid and rather enlarged and sharp trichomes. It has fibrous roots and slightly angular stems. Its ovate-cordate leaves have petioles of up to 30 cm and measure 10 to 30 x 15 to 40 cm. They have white spots, number three to live and are lobulate with triangular or elliptical lobules. The margins are denticulate to serrate-denticulate. There are two to four ramified tendrils and pentamerous, solitary, axillary flowers. The male flowers are on pedicels of 10 to 20 cm and have a campanulate calyx of 5 to 20 x 8 to 25 mm. Their sepals are linear-lanceolate or (rarely) foliaceous and are 10 to 35 mm long. They have a tubular-campanulate corolla that is yellow to orange, 6 to 12 cm long, with five lobules for up to one-third of its total length and they have three stamens. The female flowers grow on sturdy peduncles of 2 to 3.5 cm; have a globose, ovoid-elliptical, botuliforrn or piriform, multilocular ovary, a small calyx and a corolla that is somewhat bigger than that of the male flowers. They have three stigmas. The fruit is short or long and piriform, straight or curved in the thinnest part and 11 to 50 cm long. It has a hard rind which is smooth to slightly ribbed, and is white with longitudinal green reticulate stripes or completely white. The flesh is white, yellow or orange, the seeds elliptical and slightly inflated, measuring 15 to 30 x 8 to 16 mm, with a white, smooth and even testa.

FIGURE 5 Mesoamerican cucurbits: A) Cucurbitaargyrosperma; A1) leaf; A2) fruit; A3) seed; B) C pepo; B1) leaf; B2) fruit; B3) seed; C) C. moschata; C1) leaf; C2) fruit; C3) seed; D) C. ficifolia; D1) leaf; D2) fruit; D3) seed

Ecology and phytogeography

The three cultivated varieties of C. argyrosperma are found in a relatively wide range of altitudes (0 to 1 800 m), generally in areas with a hot, fairly dry climate or a well-defined rainy season. The species does not tolerate very low temperatures, which limits its cultivation to the altitudes mentioned. Each cultivated variety has a fairly defined distribution model, although there are some areas where two varieties can be found cultivated simultaneously.

In Mexico, the var. argyrosperma is grown on the slope of the gulf (Tamaulipas, San Luis Potosi, Puebla, Veracruz, Tabasco, Chiapas and Yucatan). In Central America it has been recorded in Belize, Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica and Panama. The var. callicarpa is found mainly on the Pacific slope, from the southeastern United States to central Mexico (Sonora, Sinaloa, Chihuahua, Zacatecas, Guanajuato, Nayarit and Jalisco). The var. stenosperma is endemic to Mexico and is grown in the central and southeastern states (Guerrero, Morelos, Michoacan and Oaxaca) as well as in some areas of the gulf slope (Veracruz and Yucatan).

Genetic diversity

Limits of genetic stock. Knowledge of the genetic relations of C. argyrosperma Huber and the consequent inclusion and definition of wild and cultivated taxa within its taxonomic limits have considerably widened the species" genetic stock. This includes: the local races of the cultivated varieties in the southeastern United States, Mexico and Central America; the two wild taxa of the complex (var. palmieri and ssp. sororia); and, in the United States, Green Striped Cushaw, White Cushaw, Magdalena Striped, Papago, Silver Seed Gourd, Japanese Pie, Hopi, Taos, Parral Cushaw and Veracruz Pepita.

Hybridization experiments of the taxa belonging to C. argyrosperma with other wild and cultivated taxa of the genus and some field observations have revealed that, with the cultivated species, C. moschata has the highest degree of compatibility. A second level of compatibility consists of the wild and cultivated taxa of C. pepo, some cultivars of C. maxima and the wild perennial species of C. foetidissima H.B.K. A third group is formed by C. lundelliana L. Bailey, and C. martinezii L. Bailey, with which crossings only produced fruit without viable seeds. The fourth and last group includes the perennial species C. pedatifolia L. Bailey, C digitata A. Gray, in the broad sense and C. radicans Naudin, with which only a few fruits were able to be obtained but generally without viable seeds.

The wild species that have shown some degree of compatibility with the taxa of the complex C. argyrosperma possess genes resistant to some viral diseases that have a high incidence in the cultivated species.

However, because of two actors relating to interspecific crossings, some obstacles will have to be overcome before a successful plant improvement programme including all the taxa is carried out:

· hybrids with viable seeds were not always produced;
· when some success was achieved, the plant receiving the pollen was always from the complex C. argyrosperma and, in the case of the species of the last two groups, it always involved var. palmieri or ssp. sororia.

Germplasm collections. Germplasm collections are not so scarce for the cultivated taxa but they are in very short supply in the case of the wild ones. Most of the accessions come from Mexico and are deposited in the ClFAP's gene bank in Mexico and in the USDA's in the United States.

Cultivation practices

The cultivated varieties of Cucurbita argyrosperma are worked in the traditional heavy rain agricultural systems and are sown at the start of the rainy period (May-June). Development of these varieties lasts five to seven months; the young fruit for vegetables is harvested approximately three months after being sown, while the ripe fruit for seed is harvested between October and December.

In the Mixe region of the state of Oaxaca, var. stenosperma is also grown in the dry season on so-called humid ground. This practice is also recorded in some parts of the state of Sonora in northeastern Mexico, where some cultivars of var. callicarpa can be grown in the dry season, but always with the help of irrigation to ensure production throughout the year.

The only form of propagation is the sowing of seed which is done along with some of the traditional crops of this agricultural model (maize, beans and other species of Cucurbita). In some regions of Yucatan, Quintana Roo and Oaxaca the seeds of C. argyrosperma are often the first to be planted in the maize fields. Sowing begins shortly before the start of the rain and before the other associated crops are sown.

In some localities of Yucatán. sowing is done very quickly the day after the traditional burning of the stubble of the previous crop and long before the first rain and the sowing of other associated crops. The aim is to prevent the development of weeds which would affect production of the other species cultivated in the maize field, utilizing the rapidity of growth and cover attained by this species. Practices of this type show that the seeds of C. argyrosperma are completely suited to these regions and germinate even in conditions of low humidity.

Unlike other cultivated species of the genus, it is less frequent for varieties of the argyrosperma complex to be found in vegetable gardens or plots or in small agricultural holdings or to be associated with other species.

Cucurbita pepo

Botanical name: Cucurbita pepo L.
Family: Cucurbitaceae
Common names. English. pumpkin, vegetable marrow, summer pumpkin, autumn pumpkin; Spanish: calabaza (Mexico), hüicoy (Guatemala)

Origin, domestication and expansion

According to archaeological recordings, C. pepo appears to be one of the first domesticated species. The oldest remains have been found in Mexico, in the Oaxaca valley (8750 BC to AD 700) and in the caves of Ocampo, Tamaulipas (7000 to 500 BC). Its presence in the United States also dates back a long time, as the recordings in Missouri (4000 BC) and Mississippi (1400 BC) indicate. This species may have been domesticated at least on two occasions and in two different regions: in Mexico and in the eastern United States, in each case having C. fraterna and C. texana, respectively, as possible progenitors.

Eight groups of edible cultivars of C. pepo are known:

· Pumpkin (C. pepo L. var. pepo L. Bailey,) includes cultivars of creeping plants which produce spherical, oval or oblate fruit that is rounded or flat at the ends. The fruit of this group is grown to be eaten when ripe and sometimes is used as fodder.
· Scallop (C. pepo L. var. clypeata Alefield) has a semi-shrubby habit, the fruit ranges from flat to almost discoidal, with undulations or equatorial margins, and it is eaten before maturity.
· Acorn (C. pepo L. var. turbinata Paris) is both a shrubby and creeping plant with fruit which is obovoid or conical, pointed at the apex and longitudinally costate-grooved. The rind is soft, hence the fruit can be eaten in the ripe state.
· Crookneck (C. pepo L. var. torticollia Alefield) is a shrubby type, with yellow, golden or white fruit which is claviform and curved at the distal or apical end and generally has a verrucose rind. It is eaten unripe since the rind and the flesh harden when ripe.
· Straightneck (C. pepo L. var. recticollis Paris) is a shrubby plant with yellow or golden fruit and a verrucose rind similar to that of var torticollia.
· Vegetable marrow (C. pepo L. var fastigata Paris) has creeper characteristics as a semi-shrub and has short cylindrical fruit that is slightly broader at the apex, with a smooth rind which hardens and thickens on ripening and which varies in colour from cream to dark green.
· Cocozzelle (C. pepo L. var. Ionga Paris) has cylindrical, long fruit that is slender and slightly bulbous at the apex; it is eaten in the unripe state and one of the most common names is Cocozzelle.
· Zucchini (C. pepo L. var. cylindrica Paris) is the most common group of cultivars at present. Like the previous group, the zucchini group has a strong affinity with the vegetable marrow and its origin is also recent (nineteenth century). Its plants are generally semi-shrubby and its cylindrical fruit does not broaden or else broadens only slightly. It is eaten as a vegetable in the unripe state.

With regard to traditional cultivars, it is common to see a fair representation of cultivars with characteristics similar to those of each of the commercial groups in one single field cultivated by Mesoamerican peasants. The question of the origin of the cultivars native to the Mayan area in the middle and low areas of Chiapas and the Yucatan peninsula still has to be resolved. These cultivars, whose fruits are either without or with unpronounced ribs and have rather rounded and oval seeds, are grown from a little above sea level to nearly 1 800 m.

The distribution of C. pepo outside America is possibly the best documented of this genus: it is known that some cultivars reached Europe approximately half a century after 1492 and it is even said that others originated on that continent. In contrast to C. pepo's long-established presence in the Old World, it seems that its arrival in

South America was very recent. At present, the fruit of some cultivars (for example, Zucchini and Cocozzelle) has a nutritional and commercial role in several regions of the world.

Uses and nutritional value

Like the other cultivated species of the genus, the mature or young fruit and the seeds of C. pepo, as well as to a lesser extent the flowers and young tips of the stems, are eaten in many parts of its native distribution area and in other regions of the world. C. pepo's nutrient content is similar to that described for the other cultivated species.

Botanical description

C. pepo has: creeping plants which are compact or semi-shrubby, annual, monoecious and pubescent-scabrous; broadly ovate-cordate to triangular-cordate leaves, 20 to 30 x 20 to 35 cm, with or without white spots, often with three to five deep lobules, and with denticulate to serrate denticulate margins. Tendrils have two to six branchlets, or are simple and little developed tendrils in the semi-shrubby types. It has pentamerous, solitary, axillary flowers, the males of which have pedicels 7 to 20 cm in length, a campanulate calyx of 9 to 12 mm, linear sepals of 12 to 25 x 1 to 2 mm, a tubular/campanulate corolla, 5 to 10 cm long, which is divided into five for up to one-third or more of its length; and three stamens. The female flowers have sturdy, sulcated pedicels of 2 to 5 cm; the ovary is globose, oblate, ovoid, cylindrical, rarely piriform, smooth, ribbed or verrucose and multilocular; and the calyx is very small. The fruit is very variable in size and shape: smooth to heavily ribbed, often verrucose and rarely smooth, with a rigid skin varying in colour from light to dark green, plain to minutely speckled with cream or green contrasting with yellow, orange or two-coloured. The flesh is cream to yellowish or pale orange; it ranges from soft and not bitter to fibrous and bitter, has numerous seeds which are narrowly or broadly elliptical or rarely orbicular, slightly flattened and 3 to 20 x 4 to 12 mm.

Ecology and phytogeography

Traditionally, C. pepo is cultivated from North America to Central America and in some parts of South America, although it is generally said to be a crop of high areas. Like C. moschata, this species covers a fairly wide range of altitudes. In Mexico, there are native varieties which grow from very close to sea level and in semi-dry climates, such as the variety called tsol in Yucatan, to others which are cultivated at altitudes greater than 2 000 m, such as those called güiches in Oaxaca. In Guatemala, the native cultivars, commonly called güicoy, are grown above 1 000 m, while tsols are sown in the low, hot humid parts of the Peten below 500 m.

Genetic diversity

Limits of genetic stock. The primary genetic stock of C. pepo is formed by the groups of edible cultivars (ssp. pepo) and ornamental cultivars (ssp. ovifera) as well as wild taxa (C.fraterna and C. texana).

There are a great number of commercial cultivars with particular characteristics which, together with the local varieties referred to which are grown mainly in Mexico, constitute an extraordinary genetic stock. However, in contrast to other species, this diversity does not represent an important source of genes resistant to pests and diseases, since C. pepo (including C. texana) is probably the species with the greatest susceptibility to the most important viral diseases that attack cultivated species of Cucurbita.

Species that might represent a secondary genetic stock are scarce, as most of the attempts at hybridizing C. pepo with other wild or cultivated species have required special techniques such as embryo culture; however. good results with hybridization have been achieved in Mexico and the United States.

Germplasm collections. Data obtained from the gene banks show that C. pepo is the species of the genus with the second highest number of accessions (I 135). However, this refers only to cultivated and edible forms, since those corresponding to the two closest wild relatives are very scarce and. in fact, those of C. fraterna were completed only very recently. The gene banks with the greatest representation of C. pepo cultivars are in the United States, Mexico and Costa Rica.

Cultivation practices

In its native area of distribution, C. pepo is grown both in maize fields and vegetable gardens as well as in other more intensive systems. In the former case, it is combined with maize, beans and/or with one to three of the other cultivated species of Cucurbita while in the latter system it may be found growing on plots or in small groups, generally combined with other vegetables. Where it is grown commercially, it is generally found as the sole crop, occupying areas of varying size.

In the region of Mixteca Alta, Mexico, and particularly in San Andrés Lagunas, some local variants have been found which are grown under two different sets of conditions and at two different times. One of these is known as heavy rain gourd (calabaza de temporal); it is grown on rocky ground, generally with abundant outcrops of limestone and commonly with little soil - that is, on dry ground. Sowing takes place in April and May, depending on the appearance of the first rains, and the ripe fruit is harvested in October and November. Another variant is known as the bowl gourd (calabaza de cajete); it is grown on ground called cajete (bowl), which is very flat and humid and situated in small valleys which are said to have once been occupied by lakes. In this form, it is sown at the start of the driest period of the year (February or March) and the ripe fruit is harvested between July and September.

In Yucatan, the tsol or"mensejo" variety is grown, generally in vegetable gardens or intensive husbandry systems such as those called conucos (small farms) and pachpakal, and very rarely in maize fields. It is a short-cycle variety; sowing takes place approximately 15 to 20 days after the start of the heavy rainstorms (from May to June); the unripe fruit for use as vegetables is harvested from August onwards, while the ripe fruit is available between September and October.

Prospects for improvement

The three species Cucurbita argyrosperma. C. moschata and C. pepo complement one another in their natural areas of production, which range from 0 to 2 000 m in their region of origin. In the latter, evaluation of the primitive cultivars needs to be stepped up and their germplasm used to develop new cultivars that are more productive and of greater food value, or that are resistant to diseases. especially viruses. As has already been shown in the case of some species, there are also local varieties which differ in their production period. The direct use of these, or of the genes that determine this characteristic, would allow their period of availability at markets to be extended.

The germplasm of the four species of Cucurbita should be urgently collected in their area of natural distribution. Introducing varieties present in other areas, such as C. moschata varieties which are found in Africa and have a high carotene content, and incorporating them in genetic improvement programmes is also a matter of urgency.

Boosting consumption, whether local or in the form of exports, requires the fruit to possess characteristics adapted to consignment and storage. There is a wide diversity of such characteristics which can be used to produce superior varieties.

Cucurbita spp. offer possible new uses or more intensive uses. which can be widely promoted. One is the preparation of purees or similar foods, for which there would be a very extensive genetic stock for determining organoleptic or nutritional characteristics, resulting in a product superior to the one existing on the markets and which is derived from other products. We ought also to explore the possibility of increasing the use of young stems, which are the part of the plant with the greatest food value because of the amino acid and vitamin content. Varieties which produce more foliage could even be bred for this purpose.

The use of seeds as dried fruit is common in some areas of Mesoamerica and almost unknown in others. The seeds are a good source of protein and oil, and their industrial preparation and marketing should be investigated.

There is still much to be done in terms of the collection, conservation, evaluation and use of regional or local varieties. These tasks are feasible, as the range of these crops is still to be found in the rural communities of the New World. We should not pass up the opportunity of utilizing this material to produce superior varieties and conserve their germplasm for future use.

Cucurbita moschata

Botanical name: Cucurbita moschata (Duchesne ex Lam.) Duchesne ex Poiret
Family: Cucurbitaceae
Common names. English. pumpkin, winter squash, musky squash, cushaw; Nahuatl: tamalayota (Mexico, Colombia [Guerrero]): Spanish: calabaza (Mexico), ayote (Guatemala to Costa Rica), auyama (Panama to Venezuela), zapallo (Ecuador, Peru). joko (Bolivia)

Origin, domestication and distribution

It was thought that C. moschata. like Cucurbita ficifolia, was of Asiatic origin. However, it is now evident that it was domesticated in Latin America, although it is still unclear what the precise area of domestication of either species was. On numerous occasions, it has been reported to be in Mesoamerica and on other occasions in South America, more specifically with its centre of origin in Colombia. The vestiges available are undoubtedly difficult to interpret. The oldest archaeological remains of this species were found in northwestern Mexico (the caves of Ocampo, Tamaulipas) and date from 4900 to 3500 BC. Remains are also known in northern Belize. in Tikal, Guatemala (2000 B< to Al) 850), and in Huaca Prieta, Peru (3000 BC).

Electrophoretic analysis of isoenzymes has not provided any substantial evidence. However, it has enabled us to reaffirm the strong relationship between this species and taxa of the C. argyrosperma group. Nor is the linguistic evidence very clear: C. moschata is known by native names both in the Mesoamerican region (mainly in Mexico) and in South America: this, on the other hand, supports the observation that both regions correspond to two centres of the crop's diversification.

Furthermore, the variation in C. moschata does not suggest any region in particular as the centre of origin, since this species is extremely variable in the morphology of its fruit and seeds.

The geographical distribution of the known archaeological remains of C. moschata indicate that it has been cultivated for more than 5 000 to 6 000 years. Its spread to other countries, both within Latin America and outside the continent, was certainly very early. This is shown by the existence of the variety called Seminole Pumpkin, grown since pre-Columbian times by indigenous groups of Florida in the United States, and also by its appearance in seventeenth century botanical illustrations. Such an early spread must have been very continuous and intense since, in the last decade of the nineteenth century, the species was cultivated in India, Java, Angola and Japan.

Uses and nutritional value

In the greater part of C. moschata's native area, its flowers, young stems and young and ripe fruits are eaten as a vegetable. The latter are also commonly used to prepare sweets and as fodder. The seeds are eaten whole, roasted or toasted and are ground into different stews. They have high oil and protein contents (similar to those noted in C. argyrosperma) and their consumption in urban areas is also fairly common.

Botanical description

C. moschata is a creeping and climbing plant. It is herbaceous, annual, monoecious, lightly and densely pubescent, with short and long uniseriate trichomes and caulescent vegetative apices that are fairly reflexed. It has slightly angular stems. Its leaves have petioles of 30 cm or more, are broadly ovate-cordate to suborbicular, measure 20 to 25 x 25 to 30 cm, have white spots, are slightly lobate with three to five ovate or triangular lobules, have an obtuse apex that is briefly apiculate, serrate-denticulate margins and three to five ramified tendrils. C. moschata has pentamerous, solitary, axillary flowers. The male flowers have 16 to 18 cm pedicels and a very short calyx, are broadly campanulate to pateriform, expanded or foliaceous towards the apex, 5 to 13.5 cm long, with five divisions for up to one-third of their length. The female flowers have thick pedicels of 3 to 8 cm in length, and a globose, ovoid, oblate, cylindrical, piriform, conical, turbinate ovary. They have a very small calyx and sepals that are more often foliaceous than in the males, measure up to 7.5 cm in length and are of thickened style. They have three lobate stigmas. The fruit varies greatly in size and shape (generally following the form of the ovary): smooth or with rounded ribs, rarely verrucose or granulose, with a rind that is both thickened and durable and soft and smooth, and of a very variable colour - light green to uniform dark green or with cream spots, light to dark, or completely white. The flesh is light or bright orange to greenish, ranges from light to very sweet, is soft and generally not fibrous. It has numerous seeds which are ovate/elliptical, measuring 8 to 21 x 5 to 11 mm and which have a yellowish-white surface.

Ecology and phytogeography

In botanical literature, C. moschata is reported as being grown mainly in areas of low altitude with a hot climate with high humidity. However, while it is true that this species is preferentially grown within these limits, they do not appear to be strictly adhered to, as variants have recently been found above 2 200 m in Oaxaca, Mexico.

Genetic diversity

Limits of genetic stock. The wide range of altitudes at which C. moschata is cultivated within the American continent, the considerable morphological diversity of its seeds and fruit (colour, shape, thickness and durability of the fruit's skin), the existence of varieties with life cycles of different duration as well as the existence of numerous cultivars developed in other parts of the world and of local varieties with excellent agronomic characteristics, clearly indicate that the genetic variation of this species is very extensive.

Some interesting regional varieties for Latin America are those existing on the Yucatán peninsula (and possibly in other regions of Latin America), with two life cycles of different duration, and those cultivated in Guanajuato and Chiapas, in which resistance to some viral diseases was recently found. Among the former, the short cycle variety commonly grown in Mayan vegetable gardens is of great interest, since it was certainly from this that the most commercially important variety in the region was derived. It should be mentioned that those cultivated in Guanajuato and Chiapas are currently being used in genetic improvement programmes.

With regard to the sources of variation of C. moschata cultivars developed outside its area of origin, the best example is that of a cultivar, native to Nigeria, which represents the only source of resistance to certain viral diseases. The possibilities of hybridization that C. moschata has shown with other cultivated species (for example, C. maxima) enable us to affirm that there are good prospects for the improvement of these crops.

Another part of the genetic stock of C. moschata is represented by the numerous commercial cultivars that have been developed, mainly in the United States and to a lesser extent in Brazil. Prominent among these are Butternut Squash, Golden Cushaw, Large Cheese, Tennessee Sweet Potato, Kentucky Field, Menina Brasileira and others. Some of these commercial cultivars also have different levels of resistance and/or susceptibility to certain diseases, which is indicative of the wide genetic variation of this species.

Germplasm collections. C. moschata is the best represented of Cucurbita in the gene banks of America, in which more than 2 000 accessions have been deposited. These come chiefly from Mexico and Central America and to a lesser degree from South America and other regions of the world. The most important accessions are those from the United States and Costa Rica. Collectively, the accessions are made up of American material, mainly from Central America. For its part, the CIFAP collection in Mexico is possibly the most representative of C. moschata's variation in that country.

Cultivation practices

The different variants of C. moschata are grown under traditional, heavy rain agricultural systems. It is possible to find varieties grown in maize fields together with maize, beans and one or two other Cucurbits, or in vegetable gardens and other more intensively managed farmland where they are grown alone or with other species. Sowing is carried out at the start of the rainy season and the development time is approximately five to seven months, although there are varieties with a very short cycle (three to four months) such as those mentioned from the Yucatan peninsula. In the long-cycle varieties, the young fruit to be used as vegetables is harvested approximately three months after sowing, while the ripe fruit for seed is harvested mainly between the sixth and seventh month.

In the Mixe region and other regions of the state of Oaxaca, C. moschata is also grown in the cold, dry season of the year on moisture retaining ground. Cultivation is even carried out with the help of irrigation in some parts of the state of Sonora and some short-cycle varieties have also been observed on the Yucatan peninsula where they are grown for commercial purposes in humid soils or using unusual substrates (henequen fibre waste) and irrigation.

It is likely that varieties such as the ones described, and possibly others, are grown more commonly than is thought or known on the American continent. There are some old references to a considerable variation in Colombia, but its current situation has to be properly documented and evaluated.

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