Cucurbit Genetics Cooperative Report 7:73-75 (article
Natural Hybridization of Wild Cucurbita sororia Group and
Domesticated C. mixta in Southern Sonora, Mexico
Merrick, Laura C.
Cornell University, Ithaca, NY 14556 and University of
California, Davis, CA 95616
Gary P. Nabhan
Native Seeds/SEARCH, and University of Arizona, Tucson, AZ 85721
Despite numerous experimental hybrids that have been made between Cucurbita species to determine taxonomic relationships
among taxa in this genus, evidence of uncontrolled hybrids
between taxa within their natural ranges has rarely been reported
(1). The following observations and ethnobotanical interviews
suggest that C. mixta land races long-cultivated by
Sonoran Indians may continue to exchange genes with wild or weedy Cucurbita native to northwest Mexico.
In Sinaloa and adjacent Sonora and Chihuahua, botanists have
collected numerous herbaria specimens of a wild Cucurbita belonging to the C. sororia group as it is defined by
several authors (2,3). This group is supposedly represented by C. palmeri in the north, but their leaves are not as
deeply lobed as C. palmeri described by Bailey (4).
Sonoran specimens have sometimes been referred to as the more
southerly C. sororia. Merrick (work in progress) is
finding high seed set in hybrids made between various species in
this group. If additional genetic and biogeographic work
indicate that these taxa form one highly interfertile but
variable, widespread compilospecies, the name C. radicans Naud. (4) has precedence. These taxa are closely clustered with C. mixta in numerical taxonomic studies and, as a group
including C. mixta, are distinct from other Cucurbita species (3,5). Supporting evidence from
crossing studies (Merrick, unpublished data) indicates fertile
hybrids can be produced in controlled reciprocal crosses between C. mixta and C. sororia group taxa collected
throughout the geographical range of these species in Mexico.
More restricted crossability was found in experimental crosses
between C. mixta/C. sororia group taxa and other Cucurbita wild and cultivated species. In native
habitats, the flowering phenology, basic floral morphology, and
pollinators of neighboring wild and cultivated Cucurbita are often the same, resulting in potentially suitable conditions
for gene flow. Have C. sororia group taxa possibly
contributed genes to C. mixta during its evolution under
Ethnobotanical evidence from areas of native agriculture in
Northwest Mexico suggests occasional gene exchange. In August
1970, ethnobiologist Campbell Pennington collected seed of
"calabasa caliente" in the Mountain Pima Indian locality of
Yecora, Sonora. Dr. Thomas Whitaker gave them a preliminary i.d.
of C. mixta "Taos type". Upon growout as Native
Seeds/SEARCH #EO1-015, its seed produced round, nearly softball
size fruit with extremely bitter flesh, and a peduncle less corky
or enlarged than most C. mixta. Expression of the
dominant Bi gene for cucurbitacin content, intermediate
fruit size and relatively thin peduncle suggest that this may
represent progeny of a C. mixta X C. sororia group
hybrid from Sonora. Drs. Whitaker and Bemis have viewed the
fruit and concurred with this hypothesis; progeny will continue
to be evaluated.
While collecting plants in southern Sonora, each of us has
encountered other possible evidence of such introgression. In
September 1982, L.M. visited the garden of Indian Valentin
Sasueta in the Mayo-Warihio community of San Bernardo. From his
fence, she harvested fruits (#293) which matched the description
given above for #EOI-015. Two other accessions (#294A and #294B)
with relatively large fruit were obtained at a nearby airport
landing strip not far from cultivated fields in the Alamos
municipality. Grown out in Davis, #294B appeared to be an
"escaped" C. mixta. It produced large fruits with non-
bitter flesh, thickened peduncles, large seeds and C.
mixta-type flowers. In Davis, plants of #293, #294A, and
Sonoran accessions #EO2-001 and #EO2-003 from C.N. produced
fruits of intermediate size (compared to over 90 accessions of C. mixta and over 40 accessions of wild C. sororia group taxa), bitter flesh, enlarged peduncles and relatively
large C. mixta-like foliage and stem characteristics. The
seeds of these accessions resembled those of the C. mixta "green striped cushaw type" (6) land races cultivated in
Northwestern Mexico (seed body shiny white, seed margin tan), but
were distinctly smaller. The preceding characters match those
found in experimentally produced C. mixta/C.
sororia group taxa hybrids. The bitter Sonoran accessions
exhibited variation between and within accessions for fruit size,
shape, and coloration; floral characteristics; seed size and
shape; and leaf coloration. These accessions have traits similar
to those reported by Whitaker and Gentry (pers. comm.) as wild C. mixta from the Warihio Indian region around Alamos, and
are often called "Chi Chi Coyote" or "Calabasa de Coyote" in
Spanish, and "Ha'la'we Chipu" (Bitter Squash) in the native
Warihio tongue (Eric Rowell, pers. comm.). Fruits of #293,
#294A, and #294B were called "Chi Chi Coyote" by San Bernardo
In August 1983, G.N. was accompanied by Mayo Indian José
Valenzuela into the sierras between San Bernardo, Sonora and the
Chihuahua border. At the edge of a slash-and-burn field, he
pointed out a wild Cucurbita which he said was very
bitter. He then volunteered in Spanish: "It is called Chi Chi
Coyota. If Chi Chi Coyota is on the edge of your fields, and you
plant squashes, you are going to lose them (for use) because the
bad will enter the good (squashes)." The trouble, he added, is
that it is difficult to tell this weed from the domesticated
plant until the fruit begins to mature. He said that only the
burros will try to eat its bitter gourds.
The folk term "Chi Chi Coyote" or its variants are used as well
for the xerophytic wild Cucurbita of Northwest Mexico. In
Baja California Norte, in the Sierra Juarez, a Mexican told G.N.
that this was because they are sometimes used by mothers to
discourage their children from further nursing. To wean a child,
the cucurbitacin-rich, wet pulp of maturing fruit is rubbed on
the woman's breast. After one "surprise", the child no longer
wants to nurse. Perhaps this folk name is derived from "Coyote's
Breasts" (breasts=chichis in Mexican vernacular), the Coyote
being a supreme trickster in New World folklore. Sonoran and
Arizona Indians associate Coyote with other wild relatives of
their crops, including species of Nicotiana, Proboscidea, Gossypium, Phaseolus, and even Cucumis (C. angularis) (7). Their recognition of
the close affinity of C. sororia group taxa with C.
mixta predates that of Western scientists. Further studies
will hopefully confirm this genetic introgression hypothesis and
possibly establish that C. mixta evolution is non-centric,
or diffuse in the geographical area from which it evolved and
diverged from wild Cucurbita progenitors. Since southern
Sonora borders on the true Sonoran Desert, this gene pool may be
a source of genes conferring drought and heat resistance of use
in the improvement of stress tolerance in C. mixta and C. pepo.
- Bemis, W.P. and T.W. Whitaker. 1965. Natural hybridization
between Cucurbita digitata and C. palmata. Madrono 18:39-47.
- Hurd, P.D., Jr., E.G. Linsley and T.W. Whitaker. 1971. Squash
and Gourd Bees Bees (Peponapsis, Xenoglossa) and the origin of
the cultivated Cucurbita. Evolution 25:218-234.
- Rhodes. A.M., W.P. Bemis, T.W. Whitaker and S.G. Carmer. 1968.
Numerical taxonomic study of Cucurbita. Brittonia 20:251-266.
Bailey, L.H. 1943. Species of Cucurbita. Centes Herb.VI (V):266-322.
- Bemis, W.P., A.M. Rhodes, T.W. Whitaker and S.G. Carmer. 1970.
Numerical taxonomy applied to Cucurbita relationships. Amer
Jour. Bot. 57:404-412.
- Cutler, H.C., and T.W. Whitaker. 1956. Cucurbita mlxta Pang.:
Its classification and relationships. Bull. Torr. Bot. Club
- Nabhan, G.P. 1982. The Desert Smells Like Rain: A Naturalist in
Papago Indian Country. North Point Press, Berkeley CA.