Cucurbit Genetics Cooperative Report 10:87 (article 46) 1987
Downy Mildew Resistance in Cucurbita
R. W. Robinson
Horticultural Sciences Department, New York State Agricultural Experiment
Station, Geneva, NY
C. A. John 1
Castle Seed Co., Homestead, Florida 33031
Cucurbita ecuadorensis and C. okeechobeensis are generally considered to be not very closely related. They were placed
in different groups, when Cucurbita species were classified for similarity
by numerical taxonomy (1), isozymes (4), and gourd bee relationships (3).
Thus, it is surprising that they can be crossed easily. The cross was first
made by Cutler and Whitaker (2). We obtained good fruit set for the interspecific
cross, and each fruit had many plump seed with good germination.
Both species are late to flower, but they produced both pistillate and
staminate flowers by September at Geneva, NY. The interspecific hybrid,
however, was still vegetative and had no floral buds when frost occurred
a month later. Cuttings were therefore sent to Homestead, Florida, where
the F1 plants finally flowered., in April, 11 months after the
seed was sown.
Downy mildew occurred in the planting at Florida, devastating all squash
plants in the field, except those of C. ecuadorensis x C. okeechobeensis. Since the parents of this cross were not included
in the planting, it was not possible to determine which species contributed
resistance to Pseudoperonospora cubensis. If only one of the
parental species is resistant, then downy mildew resistance must be dominant.
The interspecific F1 was crossed with C. maxima cv. Buttercup, C. moschata cv Calabaza, and with breeding
lines of C. pepo. Each 3-way cross produced viable seed that
germinated without embryo culture, although the seed was thin, due to poorly
developed cotyledonary tissue. There was a high degree of sterility in the
next generation of each cross, but selfs, sibs, and backcrosses to the cultivated
species were obtained, producing germplasm useful for breeding mildew and
virus resistant squash.
Literature Cited
- Bemis., W. P., A. M. Rhoades, T. W. Whitaker, and S. G. Carmer. 1970.
Numerical taxonomy applied to Cucurbita relationships. Amer. J.
Bot. 57:404-412.
- Cutler, H. C. and T. W. Whitaker. 1969. A new species of Cucurbita from Ecuador. Ann. Missouri Bot. Gard. 55:392-396.
- Hurd, P. D. Jr. and E. G. Linsley. 1970. A classification of the squash
and gourd bees Peponapsis and Xenoglossa (Hymenoptera: Apoidea). Univ. Calif. Publ. Entom. 62:1-39.
- Puchalski, J. T. and R. W. Robinson. 1978. Comparative analysis of
isozymes of Cucurbita species. Cucurbit Genetics Coop. Rpt. 1:28.
1 Deceased
