Interspecific hybrids in Nicotiana through in vitro culture of fertilized ovules

Abstract

N. repanda, N. stocktonii, and N. nesophila were crossed reciprocally with both diploid and tetraploid N. tabacum. Seed was obtained only when the wild species was used as the female parent and diploid N. tabacum was used as the pollen parent. While none of the seed germinated, all three desired hybrids were obtained by in vitro culture of hybrid ovules. This technique involved aseptically excising hybrid ovules from ovaries at various times following pollination and placing them on a chemically defined artificial nutrient medium. While all N. repanda × N. tabacum hybrid plants died shortly after being removed from aseptic conditions, both N. stocktonii × N. tabacum and N. nesophila × N. tabacum plants grew to maturity. In both hybrids little pairing between the two parental genomes was seen at metaphase I of meiosis, and pollen staining indicated 0 percent pollen fertility. Plants with a doubled chromosome number and partially restored fertility have been obtained for both the hybrids. Attempts are being made to use these interspecific hybrids to transfer race 1 black shank (Phytophthora parasitica var. nicotianae) resistance into commercial tobacco.