Attempts to Cross Cucurbita moschata (Duch.) Poir. ‘Butternut’ and C. pepo L. ‘Delicata’

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Cucurbit Genetics Cooperative Report 2:32-34 (article 19) 1979

J. R. Baggett
Department of Horticulture, Oregon State University, Corvallis, OR 97331

Breeders have long been interested in interspecific crosses among major Cucurbita species. Whitaker (12) reviewed the research in this area of breeding. They concluded that C. moschata occupies a central position among the annual species and can be crossed with difficulty with C. pepo, C. maxima, and C. mixta. Embryo culture and/or amphidiploidy were suggested to overcome poorly developed embryos and Fl sterility usually encountered in these crosses. They also indicated that the likelihood of success varied with cultivar used.

Erwin and Haber (4) obtained 57 fertile seeds from 4 fruit resulting from 134 pollinations of ‘Connecticut Field’ (C. pepo) x ‘Large Cheese’ (C. moschata). Many fruits and fertile seeds were produced by the F1 and F2 plants. No fertile seeds resulted from the reciprocal or from reciprocal crosses between ‘Table Queen’ (C. pepo) and ‘Large Cheese’. In these and other Cucurbita interspecific crosses, they obtained many parthenocarpic fruit. Castetter (2) also crossed ‘Connecticut Field’ x ‘Large Cheese’ with results very similar to those of Erwin and Haber (4). Wall (10) successfully crossed ‘Yankee Hybrid’ (C. pepo) X Butternut’ (C. moschata) and backcrossed the F1 with each parent. Zygote viability was greater in the backcross to ‘Butternut’ and when the F1 was used as the seed parent.

Hayase (6) achieved C. pepo x C. moschata crosses and the reciprocal, by embryo culture, but only when pollinations were made at 4:00 a.m. using pollen stored at lO°C. Rhodes (9) used C. lundelliana as a bridge by making the trispecific hybrid C. pepo x (C. lundelliana x C. moschata ‘Butternut’) and reported that bush habit could thus be transferred from C. pepoto C. moschata. Others have reported crossing C. pepo and C. moschata with varying degrees of success (1, 3, 5, 8, 13).

This report describes attempts to cross cultivars of the ‘Butternut’ group of C. moschata with C. pepo ‘Delicata’. Both natural field crossing and controlled pollinations were involved.

In 1976, plots of ‘Ponca’, ‘Patriot’, and ‘Waltham Butternut’ of C. moschata were grown in close association with ‘Delicata’ in an isolated area, but with C. pepo gourds growing about 15 m away. Seeds were saved from 15-20 fruits of each species and planted in field rows in 1977. From the combined seed of the ‘Butternut’ strains, 127 plants were grown. All were typical of the parents. Over 1,300 plants from the open pollinated ‘Delicata’ seeds were observed. Aside from a few obvious crosses with C. pepo gourds, all of these were typical of the parent and none were suspected to be ‘Delicata’ x ‘Butternut’ crosses.

In 1977, controlled reciprocal crosses were made between ‘Delicata’ and eight commercial ‘Butternut’ cultivars (Table 1). Unopened male and female flowers were tied late in the afternoon prior to anthesis. They were hand-pollinated at 08:00 to 09:00 the following day and securely bagged to prevent further pollination by bees. (There was no attempt to employ embryo culture during fruit development, and there was no examination of fruit during this period to determine if embryos were developing normally.)

Fruits were examined beginning October 1. Of the 103 pollinations involving ‘Butternut’ cultivars as female, 81% set fruit of normal size and appearance (Table 1). All 83 of the fruit were parthenocarpic with empty seedcoats. There was no practical difference in results among the ‘Butternut’ strains. The same ‘Butternut’ strains, except ‘Eastern Butternut’ and ‘Early Butternut’, were-used as parents for pollination of ‘Delicata’. Two normal size and two very small fruits resulted from 78 pollinations, but all 4 were parthenocarpic with empty seedcoats.

These results support the observations of Whitaker and Davis (12) and Erwin and Haber (4) that natural crosses between C. pepo and C. moschata rarely or never occur. Failure of 181 hand pollinations to produce seeds suggests that a ‘Butternut’ strains and ‘Delicata’ may be less promising as parents to achieve this interspecific cross than some cultivars previously used such as ‘Large Cheese’ and ‘Connecticut Field’.

Whitaker and Bohn (11) suggested that C. pepo and C. moschata should be isolated in seed production. That advice was based on the possibility of reduced seed yield through parthenocarpic fruit set. However, it is sometimes stated that C. pepo and C. moschata should be isolated because crossing will occur. In view of the results reported here and those found generally in the literature, it seems that crossing would rarely or never result from growing these species together.

Table 1. Number of fruits produced from hand crosses between ‘Butternut’ (C. moschata) strains and ‘Delicata’ (C. pepo).

Cross

Number
Pollinated
Aborted
Normal2 fruit
Butternut (Park) x Delicata 17 2 15
Eastern Butternut x Delicata 4 0 4
Early Butternut x Delicata 5 1 4
Ponca x Delicata 24 6 18
Baby Butternut x Delicata 18 5 13
Patriot x Delicata 18 5 13
Waltham Butternut x Delicata 8 0 8
Butternut (Harris) x Delicata 9 1 8
TOTALS Butternut x Delicata 103 20 83
Delicata x Butternut1 78 74 23

1‘Butternut’ strains combined; ‘Eastern Butternut or ‘Early Butternut’ not used.
2All found to be parthenocarpic.
3Plus two abnormally small fruit.

Literature Cited

  1. Bailey, L. H. 1902. A medley of pumpkins. Mem. Hort. Soc. NY 1:117-124.
  2. Castetter, E. F. 1930. Species crosses in the genus Cucurbita. Amer. J. Bot. 17:41-57.
  3. Chekalina, I. N. The efficacy of some methods of overcoming incompatibility on crossing different species of cucurbits. Sel’skokhozyaistuennaya Biologiya 8:670-672. (Plt. Breed. Abstr. 44:336, 1974).
  4. Erwin, A. T. and E. S. Haber. 1929. Species and varietal crosses in cucurbits. Bul. Iowa Agric. Exp. Sta. 263:344-372.
  5. Filov, A. I. 1963. Hybridization between cultivated and wild species of Cucurbita. Part I. Bjuli. glavnozo Bot. Sada, Moskva-Leningrad No. 51:43-48. (Plt. Breed. Abstr. 34:811, 1964).
  6. Hayase, H. 1963. Cucurbita crosses. XV. Flower pollination at 4 a.m. in the production of C. pepo x C. moschata F1 hybrids. Ikushugaki Zasshi/Jap. J. Breeding 13:76-82. (Plt. Breed. Abstr. 34:586, 1964).
  7. Hayase, H. 1963. Cucurbita crosses. XVI. Flower ages and reciprocal cross-compatibility in C. pepo, C. moschata, and C. maxima. Ikushugaki Zasshi/Jap. J. Breeding 13:159-167. (Plt. Breed. Abstr. 34:586, 1964).
  8. Pangalo, K. I. and M. K. Goldhausen. 1939. Interspecific hybridization in the genus Cucurbita. C. R. (Doklady) Acad. Sci. U.S.S.R. 24: 61-64. (Plt. Breed. Abstr. 10:60, 1940).
  9. Rhodes, A. M. 1959. Species hybridization and interspecific gene transfer in the genus Cucurbita. Proc. Amer. Soc. Hort. Sci. 74:546-551.
  10. Wall, J. R. 1961. Recombination in the genus Cucurbita. Genetics 46: 1677-1685.
  11. Whitaker, T. W. and G. W. Bohn. 1950. The taxonomy, genetics, production and uses of the cultivated species of Cucurbita. Econ. Bot. 4:52-81.
  12. Whitaker, T. W. and G. N. Davis. 1962. Cucurbits, botany, cultivation utilization. Interscience, NY, 250 pp.
  13. Yamane, Y. 1953. Studies on species hybrids in the genus Cucurbita. III. F1 hybrids of C. moschata x C. pepo with special reference to the varieties Koziku (C. moschata) and Somen (C. pepo). Biol. J. Okayama Univ. 1:202-208. (Plt. Breed. Abstr. 24:641, 1954).