Realization of the Interspecific Hybridization (F1 and BC1) Between Cucurbita pepo and C. ecuadorensis

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Cucurbit Genetics Cooperative Report 3:42 (article 23) 1980

R. Dumas de Vaulx and M. Pitrat
Station d’Amelioration des Plantes Maraicheres, I.N.R.A., Domaine Saint Maurice, 84140 Montfavet-Avignon, France

Cucurbita ecuadorensis is resistant to the most important and common diseases of C. pepo in France: powdery mildew, cucumber mosaic virus, watermelon mosaic virus (1, 2). The interspecific cross between the two species was attempted only in using C. pepo as pistillate parent (C. ecuadorensis produced no pistillate flowers in the conditions of our trials).

Observations of pollen germination of C. ecuadorensis on C. pepo stigma were made by means of fluorescence. The results were very different from one flower to the other: no pollen germination, pollen germination and short pollen tubes, and, in a few flowers, a small fraction of the pollen tubes could reach the ovule and the embryo sac.

Only parthenocarpic fruits with empty seed coats were obtained. However, some very small and white embryos (0 to 10 per fruit) were observed inside the seed coats one month after pollination. Without endosperm the embryos could not grow further. These embryos were put on a culture medium in vitro and gave rise to plants:15 viable plants were recovered from ten fruits. These plants had characteristics of the two parental species and were really F1 hybrids. By selfing the F1 plants, no fruit set was obtained.

The backcrosses with C. pepo gave fruits but the development of the embryos inside the seed coats was completely abnormal.

These embryos (10 to 40 per fruit) were transferred on a culture medium in vitro 40 or 60 days after pollination. A small fraction (10 of 100) gave rise to normal plants. The BC1plants are fertile and some normal seeds were gathered after selfing.

Literature Cited

  1. Pitrat, M. and R. Dumas de Vaulx. 1979. Recherche de geniteurs de resistance a l’Oidium et aux virusde la mosaique du Concombre et de la mosaique de la Pasteque chez Cucurbita sp. Ann. Amelior. Plantes 29:4.
  2. Provvidenti, R., R.W. Robinson and H.M. Munger. 1978. Resistance in feral species to six viruses infecting Cucurbita. Plants Dis. Rpt. 62:326-329.