II.2. SQUASHES, PUMPKINS, ZUCCHINIS, GOURDS (CURCURBITA SPECIES) – 95
2003). Smith (2006) and others (Emshwiller, 2006; Rieseberg and Harter, 2006) therefore
argue that C. pepo ssp. ovifera var. ozarkana is the most likely ancestor of cultivated
C. pepo ssp. ovifera.
With regard to the possible wild ancestor of C. pepo ssp. pepo, some authors consider
it unknown or extinct (Wilson, Doebley and Duvall, 1992; Decker-Walters et al., 2002).
That C. pepo ssp. fraterna is found on the muddy or volcanic plains of northeastern
Mexico supports the suggestion that it might be the ancestor. Sanjur et al. (2002) suggest
that C. pepo ssp. fraterna could have existed in the past in small and half-isolated
populations which were genetically divergent, and some C. pepo ssp. fraterna population
still not collected could be the possible ancestor of C. pepo ssp. pepo. Morphometric and
molecular research, as well as studies on artificial and spontaneous hybridisation support
C. pepo ssp. fraterna as a closely related wild relative. Nonetheless, at this time, no
C. pepo ssp. pepo ancestor has been identified.
Today, populations composed of C. pepo wild relatives, C. pepo ssp. fraterna,
C. pepo var. texana and C. pepo var. ozarkana, range from northeastern Mexico through
the state of Texas, east to the state of Alabama and north through the Mississippi Valley
to the state of Illinois in the United States. They occupy a diversity of environments and
ecological niches – from upland seasonally dry thornscrub habitat in northeastern Mexico
to primarily riverbanks and moist thickets in Texas, to a variety of riparian and other
disturbed lowland habitats (e.g. agricultural fields, railroad tracks and highway
embankments) throughout the Mississippi Valley. Different morphological and
physiological adaptations have evolved in these areas, including early fruit abscission
from the peduncle in response to riverine dispersal in the state of Texas, as well as
relatively quick seed germination in response to a shorter growing season in the more
northerly populations (Decker-Walters et al., 1993). In North America, C. pepo is a
morphologically and ecologically diverse species composed of genetically distinct groups
of cultivars and free-living populations (i.e. self-sustaining wild populations), all of which
are interfertile.
Following its domestication, C. pepo experienced great diversification in the
Americas and subsequent to the European contact, in Europe and Asia (Decker, 1988).
That several cultivars were known in the Americas prior to the European contact is
demonstrated by the great variability found in the first European herbaria (Whitaker,
1947; Paris, 2001, 1989). The various forms of C. pepo which were geographically
isolated in the Americas were brought together and cultivated together in European
gardens where hybridisation unavoidably occurred to produce new recombinants (Paris,
1989). C. pepo accessions are, for example, among the best represented Cucurbita
accessions at the genebank of the COMAV at the Polytechnic University at Valencia
Spain. Landraces still cultivated in Europe under traditional cropping systems
(Esteras et al., 2008) are well represented (see also Aliu et al. [2011] for a description of
C. pepo landrace diversity in the Balkans). The Newe Ya’ar Research Center in Israel
maintains a C. pepo collection with 320 accessions collected almost entirely from
North America, Europe and Asia (Paris, 2011). C. pepo is planted in all countries of
Africa on a limited scale, even though it is less tolerant of tropical conditions than
C. moschata (Grubben, 2004). Landraces or traditional varieties are maintained in
traditional cropping systems in Mexico and the northern region of Central America, and
the variation of this species in rural communities, at least in Mexico and Central America
(mainly Guatemala), is also large. It includes variants which are cultivated at altitudes
above 2000 m (during the rainy season or even the dry season on land that remains wet),
and still others that can grow near the sea and in even more extreme conditions (i.e. those