PLS221 Instructor: Carlos F. Quiros
Cucurbitacea: Cucurbita spp., Squash, pumpkins, gourds .
List of references (if unable to open download from SmartSite)
Species origin domestication and distribution
Evolutionary relationships among species
Interspecific hybridization and cytogenetics
Alien addition lines
Inheritance of important traits
Genetic markers: isozymes and RFLPs
Bridging species and utilization of wild species
Origin and domestication:
Genus Cucurbita is very rich in cultivated species, which contain the highest genomic number of all cultivated cucurbitaceae species
Most likely that polyploidy is involved in the evolution of these species.
This genus includes crops such as squash, pumpkins, and gourds.
These are indigenous of the
The Squash-Bean-Corn-Potato complex has a prominent place in agriculture, instrumental in the development of pre-Columbian civilizations
Archeological remains in a
Squash is an important source of provitamin A due to high carotene content. Cucurbitacins seem to have anti-inflammatory and anticancer activities.
27 species of Cucurbita have been described. These include immensely variable forms, fruits of different shapes, colors, and sizes.
There are 5 cultivated
species which are separated by hybrid sterility barriers. Cucurbita species are
monoecious. The cultivated species can be
differentiated from each other by different morphological traits, which are very diagnostic such as trichomes, fruit peduncle and seed margin, the most important ones.
The cultivated species were domesticated at different times and in different areas.
C. moschata: e.g: winter squash: Butternut.
C. pepo: pie pumpkins,summer squash: Zucchini, scallop, crookneck, cocozelle. This is the most variable and economically most
important species, especially in
C. argyrosperma (syn. C. mixta): winter squash: cushaw type (long, curved neck)
C. maxima: pumpkins, baking squash, buttercup, hubbard
Summer types: bushy habit, Winter types: vine habit.
C. ficifolia: Fig leaf gourd, lacayote
The annual species are classified in two main types, squashes and pumpkins, however, this separation is often not clear-cut.
Squash: fruits with fine grain flesh, mild flavor. For example varieties of C. pepo consumed immature, all baking cvs. of C. maxima. Some varieties C. pepo (acorn) and C. moschata (buttercup) baked at mature stage.
Pumpkin: fruits with coarse flesh, round shape, strong flavor, used for pies, and seed consumption.
Oldest remains for these
crops are recorded for C. pepo in
Gene pools and Distribution:
The cultivated species and their wild relatives can be classified in two large classes, and each of these in groups:
A) Mesophytic: encompass all the cultivated species:
1) C. ficifolia
C. ficifolia Found in the mountains of No.
The origin of this species is
unknown, no ancestral wild species have been found. It is predicted that it may
be somewhere in the
C. ficifolia is the most removed from the other cultivated species. It has the widest range of distribution, is a strong climber and tends to perennate. Also it shares some morphological traits of the xerophytic species.
2) C. andreana-C maxima group:
Found in So.
A diverse range of landraces
occur in So.
There are two wild species of importance related to C. maxima: C. andreana and C. ecuadorensis.
C. andreana is the probable ancestor of this cultivated species since it produces fertile hybrids with C. maxima.
3) C. moschata:
It includes butternut squash,
golden cushaw and most of the common cultivars of low
The origin and evolution of the cultigens C.argyrosperma and C. moschata may be closely intertwined. These two species functions as a connecting link between wild and the rest of the cultivated species.
4) C. fraterna-texana- pepo group:
These are found in Central
C. pepo includes the best known squashes in
5) C. sororia-C. argyrosperma group:
It includes Japanese pie
pumpkin, white cushaw and various Mexican and
Gene flow by natural hybridization in Mexico have been reported for wild C. fraterna and cultivated C. argyrosperma. Cucurbitacins were followed as markers. Isozymes indicated also gene flow from from C. pepo to C. argyrosperma which explains high identity observed between these two cultivated species.
Species in the Sororia group seem to have an important role in the evolution of Cucurbita species, originating C. moschata and C. argyrosperma. C. argyrosperma can be crossed with all the species in the group as well as with C. moschata.
6) C. lundelliana group:
Two wild species are the most important in this group: C. lundelliana and C. martinezii (fruit used as detergent).
7) C. digitata group:
It includes five wild species of which C. palmata is the most important one.
8) C. foetidissima group:
It includes three wild
species, of which C. foetidissima (
Recently this species was attempted to domesticate because of its abundant seeds rich in proteins, roots rich in carbohydrates and xerophytic nature.
Except for C. andreana and C. ecuadorensis,
all wild Cucurbita spp. occur north of
C. maxima C. andreana
Cytogenetics and interspecific hybridization:
Most of the cytogenetic research in Cucurbita species derive from interspecific hybridization studies. These have resulted in the synthesis of a few amphiploids and alien addition lines. On the basis of chromosome pairing, different genomes have been tentatively assigned.
Alien addition lines:
MMMM (C. moschata)x PPPP (C. palmata)
(Colchicine treatment of diploid MP is avoided, because it was too weak to tolerate colchicine).
MMPP x MM
MMP x MM
Interspecific aneuploids (addition lines moschata/palmata) MM + P1....P20
Three alien addition lines recovered each with a different phenotype. These were used by Weeden to locate two groups: fumarase and hard ring (Hr gene) ; Pgi and Got. These two were found linked also in C. pepo, C. maxima and C. ecuadorensis demonstrating colinearity for this segment in all 4 species.
Hybrids of C. maxima x C. ecuadorensis (virus resist):
Relatively fertile hybrid, but both F2 and BC display reduced fertility. This is attributed to hybrid breakdown or dysgenesis.
Sex determination: There is less variation on sex types in Cucurbita species than in other cucurbits. Most of the species are monoecious, with a few rare andromonoecious mutants due to recessive genes. The genus might be comparatively recent, compared to other cucurbits, because the presence of monoecious plants only indicates that Cucurbita species have not have enough time to evolve alternate sex as other cucurbits.
A gynoecious mutant has been reported for C. foetidissima, but in none of the cultivated species. It could be very useful for hybrid seed product.
Commercial hybrid seed is produced by application of 500 ppm of ethephon to seedlings, preventing the development of staminate flowers in the line used as female.
Fruit color: very complex, it changes with fruit maturity, it can go from light green to dark green ending in bright yellow. Dark fruit, allele D, light fruit color d.
Rind striping: Different types of stripes determined by multiple alleles at L-1 and L-2 loci. L-1 and L-2 are complementary resulting in intense fruit color, the recessive ones l-1 and l-2 (light coloration) produce light color over the entire fruit, a series of alleles dominant or co-dominant to l-1 and l-2 produce different types of stripping (l-1 alleles Bst, iSt, l-2 allele R produces reverse stripping (light color stripped over dark background). (Paris H, 2009)
Locus B bicolored fruits
Large array of colors, at least 9 genes involved.
Fruit shape: Disc shape due to complementary action of two dominant alleles D1 and D2, spherical, single dominant at either locus, elongated fruit results from double recessive.
Neck dominant to neckless
Naked seed, lack seed coat, inhibition of lignin synthesis in cell wall, determine by single recessive n.
Bushy mutant type determined by single gene Bu. In C. pepo and C. maxima this trait is important to produce more food in less space
Isozymes: Most of this markers have been developed for C. pepo .
Work by Ignart and Weeden (1987), at least 7 loci studied in various types of C. pepo
Some fruit types might be linked to specific enzyme loci, for example:
Spaguetti squash has unique Got-5 allozyme.
Two acorn squahes tested, also had unique pattern for the same locus.
Scallop squash has specific Got-2 allozyme.
Yellow straight neck has specific Mdh-2 allozyme.
Kirkpatric et al (1988) reported inheritance of isozymes on crosses between C. pepo and its ancestral wild species C. texana demonstrating gene flow between these species.
In squash it is possible to run electrophoresis in single pollen grains, since they are large enough to be crushed with tweezers.
Interspecific cross C. maxima x C. ecuadorensis used to identify 5 linkage groups. Extensive gene duplication for isozymes support polyploidy in Cucurbita species.
rDNA genes used for separating varieties of C. pepo by polymorphism of intergenic spacer.
Intergenic spacer in C. maxima is unusual
in the sense that it is longer than in other plants species (5.5Kb). It has 5
repetitive domains and 3 unique regions.
Genetic variation was determined by RAPD markers (Gwanma et al. 2000) in landraces of C. moschata from
Linkage map with RAPD and AFLP markers in pepo now expanded with new SSRs and genes h and B and approximately 650 markers in 20 linkage groups (Zraidi et al 2007, Gong et al 2008)
Flesh of better quality C. maxima has been used as a source to improve flesh quality of C. moschata.
It is possible to hybridize both species but the sterility of the hybrid is high.
Sakata Seed from
Widely used in cucurbita breeding.
1) C. lundelliana is an ideal bridge species since it crosses to all cultivated ones.
By crossing it to these, interbreeding populations can be established.
2) C. moschata also is useful as a bridge species. It has been used to transfer transfer disease resistance from C. martinezzi to C. pepo.
C. moschata crosses readily to C. martinezii, and the resulting hybrid crosses to C. pepo. C. martinezii does not cross directly to C. pepo. This three way cross was used to transfer powdery mildew resistance to C. pepo.
Gametic diversity helps hybridization, For
example, F1 C. pepo
hybrids are more
successful than inbred lines of C. pepo when crossed with C. moschata.
C. pepo scallop squash crosses easier with C. moschata than any other C. pepo form.
C. pepo x C. ecuadorensis
has been used to to transfer multiple disease
resistances, but embryo
culture is necessary.
Not much work done in the past, compared to cucumbers and muskmelons.
Absence of good sources of resistance in cultivated germplasm. It is necessary to use wild species. Wild species as a rule are virus resistant.
C. martinezii is resistant to CMV.
C. ecuadorensis and C. foetidissima, are resistant to watermelon mosaics 1 and 2. Also squash mosaic virus tolerance found in above species.
Silvered leaves seems to deter virus transmitting aphids, determined by gene M.
Biotechnology: This area needs to be developed in squash and pumpkins. Transformation techniques by Agrobacterium rhizogenes is available. Transgenic virus resistant zucchini is one of the few transgenic crops commercially available.
Haploids obtained by pollen irradiation with gamma rays in C. pepo, the most effective doses were 25 to 50 Gy.
Last modified, May 5th, 2010
© Carlos F Quiros, 1998