Overcoming Cross-incompatibility between Nicotiana tabacum L. and N.rustica L. by Test-tube Pollination and Ovule Culture

Interspecific hybrids between Nicotiana tabacum (=) and N.rustica can not be obtained by conventional crossing because of cross-incompatibilit.y. Two techniques, test-tube pollination and ovule culture, were combined to overcome cross-incompatible combination. Whole placentae with intact ovules of N.tabacum were pollinated in vitro by dusting pollen grains of N.rustica. Developed ovules were excised from the placentae and transferred to ovule culture. Finally, 12 hybrid plants were obtained by the combination of these two techniques. The hybrid plants were intermediate between their parents in their morphological appearance and had 48 chromosomes which were the additive sum of the haploid chromosomes of the parents. They failed to produce fertile pollen and were completely self-sterile. A fertile chromosome-doubled hybrid was obtained by colchicine treatment. From the results, it is considered that the combination of two techniques, test-tube pollination and ovule culture, is useful for overcoming cross-incompatibility between distantly related species.