Somatic hybridization in Nicotiana: behavior of organelles after fusion of protoplasts from male-fertile and male-sterile cultivars.

Protoplasts from a nitrate reductase-deficient mutant of Nicotiana tabacum (cnx-68) were fused with protoplasts of 3 different cytoplasmically male-sterile cultivars of tobacco. Two cultivars had no stamens in the mature flowers and the third had petaloid structures in place of the stamens. Plants were regenerated from the fused protoplasts and characterized with respect to stamen development, chromosome number, and two chloroplast-coded traits. Nearly all hybrid plants displayed the chloroplast traits of only one parent, indicating that chloroplast segregation had occurred. The frequency of appearance of each chloroplast type differed according to the species origin of the chloroplasts. Chloroplasts from N. undulata competed much better than those from N. tabacum; N. suaveolens somewhat better than N. tabacum; and N. glauca about equally with N. tabacum. These results are compatible with an interpretation that equal frequency of appearance of chloroplast type among the regenerated plants occurs if the chloroplast DNAs of the parents are similar, whereas a bias of chloroplast type appears among the regenerated plants when the chloroplast DNAs are different. The appearance of aberrations in stamen development resembling the cytoplasmic male-sterile parental types was infrequent among the hybrid plants in all three crosses. Thus sterility factors were generally overcome by fertility factors following somatic hybridization.