ARS | Publication request: SYNTHESIS AND PRELIMINARY CHARACTERIZATION OF A NEW SPECIES (AMPHIDIPLOID) IN CUCUMIS

Submitted to: Journal of Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 6, 2001
Publication Date: N/A

Interpretive Summary: Research has indicated that the genetic variation that exists in cucumber is limited and that ways to increase the genetic diversity should be sought. One way to increase the genetic variation in cucumber is to introduce genes from its wild relatives by traditional breeding (manual transfer of pollen from one plant onto the ovary of another plant). Because of the complex genetic nature of cucumber and the fact that it is reproductively isolated (cannot mate with wild species) it has not been possible to transfer genes from wild relatives of cucumber (mainly found in Africa) to increase genetic diversity. Our USDA, ARS laboratory has succeeded to produce a hybrid between a wild species (Hystrox) and cucumber. We have overcome sterility in the hybrid to produce fertile females by embryo disseron to stimulate embryo growth. The recovery of these fertile plants was the first successful hybridization of a cultivated dand a wild species in cucumber, and represents a real possibility of increasing the genetic diversity of cucumber. For instance, nematode resistance is present in hystrix and absent in commercial cultivars. The impact to cucumber breeding is that researchers can now incorporate nematode resistance into cucumber plants through strategic cross pollination. Since damage from nematodes results in significant losses in yield and quality, the incorporation of such resistance will greatly increase profit to the U.S. grower.

Technical Abstract: A successful interspecific hybridization between cucumber (Cucumis sativus L., 2n = 14) and a wild Cucumis species, C. hystrix Chakr. (2n = 24) was made via embryo rescue. Hybrid plants (2n = 19, 7 from cucumber and 12 from C. hystrix) were sterile, but morphologically uniform. Self- pollinat nd backcrossing of F1 hybrid plants to either parent confirmed the presence of both male and female sterility that were likely caused by lack of homology and improper pairing during meiosis. While the multiple branching habit, densely brown hairs (on corolla and pistil), orange-yellow corolla, and ovate fruit of F1 hybrid plants were similar to that of the C. hystrix parent, the appearance of the first pistillate flower was more similar to that of the C. sativus parent. The diameter and internode length of the stem, and the shape and size of leaves and flowers were intermediate when compared to the parents. The chromosome number in the hybrid was doubled through somaclonal variation during embryo culture and regeneration process to restore the fertility. Pollen grains were released and fruits with viable seeds matured on fertile, synthetic amphidiploid plants (2n = 38).