Attempts to Overcome the Barrier of Interspecific Hybridization Between Cucumis Melo and C. Metuliferus

The crossability of Cucumis melo and C. metuliferus was studied in order to find ways to effect the cross between the two species. In cross-pollination within C. melo, the pollen tubes entered the ovarian cavity within 24 h, and fertilization occurred within 48 h. Pollen germinated well after cross-pollination between the species, but pollen tubes grew slowly. C. metuliferus pollen tubes were arrested in the stigma or the upper style of C. melo flowers. The influence of 100-, 150-, and 200-krad gamma radiation on in vitro germination, pollen tube growth of C. melo and C. metuliferus, and on in vivo fertilization of C. melo was studied. Pollen of C. metuliferus appeared to be much less sensitive to gamma rays than that of C. melo. Higher radiation doses were found to reduce fruit set of C. melo. Irradiation of pollen of C. melo always resulted in “pseudo-fertilization”. We attempted to overcome the prefertilization crossing barrier between C. melo and C. metuliferus by using techniques of bud pollination, benzyladenine (BA) treatment, and irradiated mentor pollen. Ten lines of C. melo and 6 accessions of C. metuliferus were used as female and male parents, respectively. The techniques of BA and bud pollination were ineffective. Numerous fruits with few embryos were obtained on some of the C. melo lines after using the irradiated mentor pollen technique. Embryos, which were isolated at the age of 20–25 days and cultured on medium consisting of 1/3 Murashige and Skoog medium, were observed to provide normal development. All nine surviving plants were similar to the maternal parent and were not interspecific hybrids.