Cytogenetic studies on Nicotiana tabacum L. x Nicotiana glutinosa L. F1 hybrids

Significant differences were observed in mean percentage capsule set between reciprocals and among crosses. Nicotiana tabacum exhibited normal bivalent pairing at diakinesis while N. glutinosa exhibited univalents ranging from 2 to 18 per cell at a frequency of 26%. The other stages of meiosis in the two species were marked with relatively high frequencies of laggards but pollen fertility was high ranging from 85% to 96% in the six varieties of N. tabacum and 71% in N. glutinosa. The lower fertility of N. glutinosa was attributed to the occurrence of asynaptic/desynaptic condition from diakinesis to metaphase 1 of meiosis. The F1 interspecific hybrids exhibited a highly disturbed meiosis with the occurrence of laggards, bridges, unequal segregation, multiple spindle and micronuclei formation. Bivalent pairing at diakinesis ranged from 0 to 12 pairs with two bivalents consistently occurring at high frequencies in most crosses. Genotypic differences among N. tabacum varieties were indicated in varying frequencies of bivalents obtained in each cross combination. All the hybrids were sterile with less than 1% mean percentage pollen fertility. The F1 plants were morphologically different from either parent but more closely resembled N. tabacum in general plant stature, leaf shade and flower characteristics. Chromosome numbers observed in the doubled hybrids ranged from 60 to 72 indicating incomplete polyploidy and/or chromosome elimination. Absence of complete bivalent pairing was observed and seed capsules were produced in two of the three doubled hybrids. Ten F2 plants produced from the colchicine-derived seeds of N. glutinosa x Vizcaya exhibited a highly irregular meiosis. Two plants scored for diakinesis revealed a chromosome number of 72. Complete bivalent pairing was observed at a frequency of 60%. The rest were associations of bivalents and univalents. Only one plant produced seed capsules.