Hybridization of Cucurbita pepo with Disease Resistant Cucurbita Species

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Cucurbit Genetics Cooperative Report 6:92 (article 47) 1983

Richard L. Washek and Henry M. Munger
Cornell University, Ithaca, NY 14853

Several Cucurbita species, mostly non-cultivated, are sources of resistance to cucumber mosaic, watermelon mosaic-1, watermelon mosaic-2, squash mosaic and powdery mildew (3). Through embryo culture, C. pepo was hybridized successfully with C. martinezii (now considered synonymous with C. okeechobeensis), C. lundelliana, C. ecuadorensis, C. palmeri, and C. ficifolia.

Crosses between C. pepo and C. martinezii have been reported only once previously (1). In the present study six F1 plants of C. martinezii x C. pepo were obtained by making 206 pollinations and using embryo culture. These F1 plants were self-fertile and produced a large amount of F2 seed. Reciprocal backcrosses of F1 and F2 plants have produced only a few viable seeds. The backcross plants obtained show adequate self-fertility. In a population of over 100 F2 seedlings inoculated with CMV, all showed symptoms initially but about 25 recovered to be worthy of transplanting to the field and 2 were outstanding in freedom from symptoms. Late in the season four plants without symptoms were tested for the presence of CMV and none was found. Another F2 population was inoculated with WMV2 and several symptomless plants were found in it. Finally, 35 plants were inoculated with WMV1 and 1 plant became symptomless after showing faint mottling initially. Cuttings of this plant are available on request. Backcrossing the best F2 plants to C. pepo has given small amounts of seed from some but not from others.

Crosses between C. pepo and C. ecuadorensis have also been reported previously, but only once (2). In the present study, 30 pollinations of C. pepo x C. ecuadorensis yielded 11 F1 plants through embryo culture, all from one fruit of ‘Foodhook Zucchini’. F2 seed was not obtained; the F1 produced few male flowers and these not at the same time as females. The F1 plants in the greenhouse were pollinated by various C. pepo and several hundred embryos, some well developed, were cultured to yield 20 backcross plants for the field in 1982. Limited amounts of self- and open-pollinated seed were obtained from most of these; backcrosses were not attempted because the population was considered too small to test for resistance to the several diseases of interest. Many cuttings from the F1 plants were also grown in the field and from numerous pollinations with C. pepo, several dozen plump seeds have been obtained. The F1 plants remained free of viral symptoms in a field where cucumbers and squash had high incidence of infection with CMV and WMV2, but their powdery mildew resistance was relatively low.

The cultivated C. ficifolia was hybridized directly, through embryo culture, with 3 other cultivated species: C. pepo, C. moschata, and C. maxima. All F1 plants were characterized by high male and female sterility. The backcross of C. ficifolia x C. pepo to C. pepo yielded 5 male- and 5 female-sterile plants.

Literature Cited

  1. De Vaulx, R. D. and M. Pitrat. 1979. Interspecific cross between C. pepo and C. martinezii. Cucurbit Genetics Coop. 2:35.
  2. De Vaulx, R. D. and M. Pitrat. 1980. Realization of the interspecific hybridization (F1 and backcross 1) between C. pepo and C. ecuadorensis. Cucurbit Genetics Coop. Volume 3.
  3. Provvidenti, R., R. W. Robinson, and H. M. Munger. 1978. Multiple virus resistance in Cucurbita species. Cucurbit Genetics Coop. 1:26.