Cucurbit Genetics Cooperative Report 10:88-89 (article 47) 1987
Genetic Variability for Compatibility of an Interspecific
R. W. Robinson and J. W. Shail
Horticultural Sciences Department, New York State Agricultural Experiment
Station, Geneva, NY 14456
The cross Cucurbita pepo x C. ecuadorensis,
which is of interest for breeding squash for multiple disease resistance,
was first made by Washek (2). The cross is usually difficult to make, even
with embryo culture.
Our repeated attempts to cross C. ecuadorensis with C.
pepo cultivars 'Early Prolific Straightneck', 'Caserta', and 'Scallop'
were unsuccessful. Another C. pepo cultivar, 'Black Jack',
proved to be much more compatible in this interspecific cross (Table 1).
Fruit set was much better when 'Black Jack' was the C. pepo
parent, and hybrids with C. ecuadorensis were obtained for
'Black Jack' but not for the other C. pepo cultivars.
'Black Jack' is a zucchini-type F1 hybrid. Washek (2) also
succeeded in crossing C. ecuadorensis with a zucchini-type
cultivar of C. pepo. Thus, a 'Zucchini' gene background may
be helpful for accomplishing the interspecific cross, but more zucchini-type
cultivars need to be tested to verify this.
Even though 'Black Jack' crossed more easily with C. ecuadorensis
than did the other C. pepo cultivars tested, the cross is
still encumbered with sterility barriers. Embryo culture was required in
the initial cross, and many fruit were without embryos that could be cultured
(Table 1). Fertility of the interspecific hybrid was low, but backcross
seed was produced without embryo culture by using 'Black Jack' as the pollen
parent. The interspecific hybrid was also successfully used as the maternal
parent in crosses with C. moschata.
Both parental species are monoecious but the C. pepo x
C. ecuadorensis hybrid was gynoecious, agreeing with Washek's
observation (2). A similar phenomenon was reported (1) for the cross C.
maxima x C. moschata, which also produced a gynoecious
hybrid. Staminate flowers were induced to develop on the C. pepo
x C. ecuadorensis F1 by multiple applications of
GA4/7 or Ag(NO3)2 . However, pollen production was
scanty and no F2 seed was produced when the treated interspecific
hybrid was self- or sibpollinated. The F1 plants did produce
open-pollinated seed (Table 1), and the progeny indicated it was the result
of outcrossing with C. pepo.
- Robinson, R. W., M. A. Boettger, and J. W. Shail. 1978. Gynoecious
sex expression in Cucurbita resulting from an interspecific cross.
Cucurbit Genetics Coop. Rpt. 1:31-32.
- Washek, R. L. 1983. Cucumber mosaic resistance in summer squash (Cucurbita pepo L.). PhD. Thesis, Cornell Univ., Ithaca, NY 187 pp.