GENOMIC FACTORS CONTROLLING THE LETHALITY EXHIBITED IN THE HYBRID BETWEEN NICOTIANA SUAVEOLENS LEHM AND NICOTIANA-TABACUM-L

Interspecific hybrid plants between Nicotiana suaveolens and N. tabacu m exhibit lethal symptoms at the seedling stage and cannot grow to mat urity. In this investigation, an attempt was made to clarify the genom ic factors responsible for this lethality. N. suaveolens was crossed t o N. sylvestris (genomic constitution: SS) and N. tomentosiformis (TT) , these latter two species being the progenitors of N. tabacum (SSTT). From the cross N. suaveolens x N. tomentosiformis, many seedlings wer e obtained through ovule culture, and these subsequently grew to matur ity without exhibiting any lethality. In the reciprocal crossing betwe en N. sauvelons and N. sylvestris, only a few hybrid seedlings were ob tained through ovlue culture and all died after unfolding their cotyle dons when cultured at 28 degrees C. This lethality could be avoided by culturing the ovules at 36 degrees C. These features of hybrid lethal ity resembled those observed in the interspecific hybrid between N. su aveolens and N. tabacum. These findings suggest that the S genome in N . tabacum is responsible for the lethality exhibited in the hybrid bet ween N. suaveolens and N. tabacum.