Interploid Hybridization of Cucumis melo and C. metuliferus

The long-term motivation for this research is to transfer useful traits from a broad based gene pool of wild species into the narrow base of a cultivated crop in Cucumis. Our primary focus was to use polyploid prior to fertilization as a tool to overcome fertility barriers in the cross between C. melo and C. metuliferus. In conducting this research, we explored all combinations of tetraploid and diploid parents, in reciprocal combinations. Pollinations were made in both the field and greenhouse, using emasculated flowers, moneocious females, and open pollination by insect vectors, with morphological selection criteria. After observations of thousands of ovaries, we still have no definitive proof that this hybridization yielded viable embryos. The most promising results came from using tetraploid C. metuliferus, as the maternal parent in the interspecific hybridization, that set fruit were seeds contained small embryos that did not germinate. To obtain fruit set, it was important to rear plants in a cooler sunny greenhouse, as would be found in late winter/early spring. A second interspecific hybrid between wild and cultivated Cucumis, C. hystrix x C. sativus, yielded fertile progeny for the first time, while concomitantly working toward our primary goal. Two distinct treatments were necessary; 1) special plant husbandry was necessary to have the wild species produce fruit in cultivation, and 2) embryo rescue followed by chromosome doubling in vitro was required for fertility restoration. Backcrosses to crop species and resistance to nematodes are compelling areas for further work.