Cucurbit Genetics Cooperative Report 21:51-53 (article 18) 1998
Some Observations Concerning Diversity in the Subspecies and Horticultural Groups of Cucurbita pepo
Harry S. Paris
Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Research Center, P.O. Box 1021, Ramat Yishay 30-095, Israel
Cucurbita pepo is a highly polymorphic species. On the basis of seed morphology and allozyme variation, this species has been divided into two subspecies, pepo and ovifera (1). The eight horticultural groups of the species (7) can be easily recognized as belonging to one or the other of the subspecies. The pumpkin, vegetable marrow, cocozelle and zucchini groups belong to subspecies pepo whilst the scallop, acorn, crookneck, and straightneck groups belong to subspecies ovifera.
Besides the differences in seed morphology and allozyme variation, the subspecies are differentiated from each other by an entire set of phenotypic characteristics. The horticultural groups belonging to ssp. pepo almost always have larger fruits, larger flowers, larger seeds, and thicker peduncles than those belonging to ssp. ovifera. The fruits of ssp. pepo are smooth or grooved to very prominently ribbed (protrusion of the vein tracts) whereas those of ssp. ovifera are smooth to very prominently furrowed (depression of the vein tracts). Flecking in the fruit rind color is larger and denser in ssp. pepo than in ssp. ovifera. Silver leaf mottling, conferred by gene M., is common in ssp. pepo but almost non-existent in ssp. ovifera. Wartiness of the fruits, conferred by gene Wt, is rare in ssp. pepo but common in ssp. ovifera. Yellow fruit color, conferred by the Y, occurs only in cultivars of ssp. ovifera. The horticultural groups of ssp. pepo contain a much larger number of cultivars and more phenotypic variation than do those of ssp. ovifera.
In addition to the fruit shape differences defining them, it can be seen that the horticultural groups of C. pepo ssp. pepo are differentiated from one another fairly well on the basis of various other phenotypic characteristics, some of which are conferred by known genes. for example. seeds of zucchini cultivars are almost always shorter and more plump than those of the other groups whereas seeds of pumpkin cultivars are almost always longer and thinner. The seeds are distributed in a cavity along the entire length of the fruit in the pumpkins, zucchini, and vegetable marrows but in the cocozelles the seed cavity is restricted to approximately one-third of the length, near the stylar end. Cocozelles tend to have the largest pistillage flowers, except for some of the largest-fruited cultivars of pumpkins (9). The top-dominant L-1 allele is present in nearly all zucchini cultivars, but uncommon in the other groups. Alleles for fruit striping at the l-l locus are common in the cocozelle group but otherwise infrequent. The recessive l-2 allele, otherwise rare, is common in the vegetable marrow group. Thus, most pumpkins are l-l / l-l L-2/L-2; most vegetable marrows are l-l/l-l l-2/l-2; most cocozelles are l-lSt/l-lSt L-2/L-2; and most zucchini are L-l/L-l L-2/L-2.
Pumpkins, being round or nearly so, deviate the least in overall fruit shape from that of wild and feral forms of the species, and therefore are probably the oldest group. Pumpkins range up to 25 kg and can be smooth, with or without longitudinal grooves, or slightly to strongly ribbed. Although the familiar Halloween and pie pumpkins of the U.S.A. ad Canada turn intense orange at maturity, some cultivars from Europe and Asia Minor remain green through maturity,. Pumpkins from these locations have non-lignified rinds and thus are sliced easily, but most Mexican forms and other pumpkins used i the manner of summer squash have lignified rinds.
Vegetable marrows are probably the next oldest group of ssp. pepo, being the next closest to the ancestral fruit shape. Several forms of C. pepo having fruits similar in overall shape to vegetable marrows appeared in Europe prior to 1600. Writings in England from the 19th- and early 20th-century indicated that this group then contained a greta deal of variability. Some old-time, vining cultivars of this group, for example, 'Table Dainty' still exist. However, the vegetable marrows have suffered much genetic erosion, as many of the original variable stocks of vegetable marrows that were grown in the Middle East, generally known as 'Baladi', have been replaced by hybrids developed and offered mostly by American and French seedsmen (4). Cocozelles are the next oldest group, having long, but bulbous fruits. They were depicted in the 18th century and perhaps were described as early as the 17th century. 'Striato D'Italia' (syn, 'Napoli') is an old, variable cultivar and the likely source from which various cocozelle cultivars of Europe and the U.S.A. were derived. Many other cocozelle cultivars have been locally distributed in Italy for a very long time. Differing greatly from one another in fruit coloration, ribbing, and flecking, these local cultivars present an economically difficult situation for foreign seed companies in their attempts to introduce new cultivars. Presently, this group may harbor more genetic variation than any other group of summer squash.
A zucchini cultivar was first described around 1900. Quickly, the zucchini has become the economically most important group of the species. Although it therefore contains very many named cultivars, most of these are recently derived hybrid combinations of inbreds maintained by seed companies.
Zhiteneva (10) presented photographs of C. pepo collected in Mexico and Asia Minor. Comparing the photos, it is easily seen that the Mexican material does not contain the long-fruitedness found in the Asian material. This would seem to indicate that in the Old World, C. pepo had been selected more rigorously for long-fruitedness and adaptation of the young fruits to culinary purposes. Possibly, selection may have been easier in Asia because of isolation from primitive, weedy or wild round-fruited forms occurr8ing in the native habitat, Mexico. Another possibility, not exclusive of the first, is that the use of C. pepo ssp. pepo for seed consumption was more important in Mexico.
Most pumpkins, of course, are very viney. Many vegetable marrows of yore were viney (2) and at least two vining vegetable marrow cultivars are extant, 'Table Dainty' and 'Vegetable Spaghetti'. Naudin (5) knew of at least one vining cocozelle. Some cocozelle stocks, while not viney, have distinctly longer internodes than others. I have not encountered, in the literatur4e or personally, a zucchini cultivar that was vining, or even that had long internodes. As Pangalo (6) noted, bush growth habit and short internodes are characteristics derived under cultivation. That zucchini cultivars are never viney or long-internoded could only indicate that they were recently derived.
Other observations provide further insight concerning the history and relationships within C. pepo ssp. pepo. Landraces of C. pepo have been collected in remote regions of Italy by Hammer, Perrino, and colleagues (3, 8). I have obtained seeds of 14 of the C. pepo samples they collected. All belong to spp. pepo. Of the 14, four are pumpkins (including summer pumpkins), three are cocozelles, three are vegetable marrows, one has a unique fruit shape nd three are mixed stocks. There is not a single zucchini among these, again indicative of the relatively recent origin of the zucchini group. All of the accessions are bushy, but some have noticeably longer internodes than the others.
Tapey et al. (9) wrote that the zucchini originated in Italy and was introduced into the United States around 1920. All of the open-pollinated zucchini cultivars of Italy known to me contain Milano" in their names. As at least three, 'Nero di Milano', 'Verde di Milano' and 'Verde Lungo di Milano', are quite distinct from one another, it seems that Milan and its environs are the specific locality for origination of the zucchini group. This geographic origin is strikingly more restricted and very different from that of the cocozelles, whose local Italian cultivars bear the names of a number of cities and provinces located further south and east, indicating a much wider distribution: Florence, Tuscany, Rome, Faenza, Genoa, Naples, Puglia, and Sicily
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