PRODUCTION AND CHARACTERIZATION OF TOBACCO ADDITION LINES CARRYING NICOTIANA-DEBNEYI CHROMOSOMES WITH A GENE FOR RESISTANCE TO BLACK ROOT-ROT

Black root rot, caused by Chalara elegans Nag. Raj and Kendrick (syn: Thielaviopsis basicola [Berk. and Broome] Ferr.), is a common soil-bor ne fungal disease in cultivated tobacco (Nicotiana tabacum L., 2n = SS TT = 48). Only polygenic partial resistance to this disease is availab le in the original tobacco genomes; however, Nicotiana debneyi Domin, a tetraploid relative of tobacco (2n = XXYY = 48) has complete resista nce to a wide spectrum of black root rot biotypes. A fertile somatic h ybrid between N, tabacum 'Delgold' and N. debneyi was previously produ ced and was used to transfer the N. debneyi black root rot resistance into tobacco. Tobacco addition lines carrying the N. debneyi chromosom es with the gene for black root rot resistance were produced after two generations of backcrossing to the recurrent tobacco parent followed by two generations of selfing. Random amplified polymorphic DNA (RAPD) analyses of the disomic (2n = 50) addition lines and 14 monosomic (2n = 49) addition lines derived there from provided strong evidence that the two N. debneyi chromosomes in the 2n = 50 addition lines were ide ntical. However, the tobacco genetic background apparently prevented h omologous pairing of these chromosomes or caused their desynapsis. Lag ging chromosomes at anaphase I and micronuclei at telophase I were obs erved. Transmission rates of the N. debneyi chromosomes through the eg g and pollen of the addition lines were 8.1 and 10.1%, respectively. T he N. debneyi chromosomes in the addition lines occasionally paired wi th tobacco chromosomes, and therefore, translocation lines with black root rot resistance (2n = 24 II) may be obtained in the self-pollinate d progeny by crossing-over. Seventeen RAPD markers were found to be as sociated with the N. debneyi chromosomes in the addition lines and the se should be useful in monitoring further transfer of N. debneyi chrom osome fragments into the tobacco genomes.