Production and Characterization of Tobacco Addition Lines Carrying Nicotiana debneyi Chromosomes with a Gene for Resistance to Black Root Rot
- Dapeng Bai ,
- R. Reeleder and
- J. E. Brandle
Black root rot, caused by Chalara elegans Nag. Raj and Kendrick (syn: Thielaviopsis basicola [Berk. and Broome] Ferr.), is a common soil-borne fungal disease in cultivated tobacco (Nicotiana tabacum L., 2n=SSTT=48). Only polygenic partial resistance to this disease is available in the original tobacco genomes; however, Nicotiana debneyi Domin, a tetraploid relative of tobacco (2n = XXYY = 48) has complete resistance to a wide spectrum of black root rot biotypes. A fertile somatic hybrid between N. tabacum ‘Delgold’ and N. debneyi was previously produced and was used to transfer the N. debneyi black root rot resistance into tobacco. Tobacco addition lines carrying the N. debneyi chromosomes 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 identical. However, the tobacco genetic background apparently prevented homologous pairing of these chromosomes or caused their desynapsis. Lagging chromosomes at anaphase I and micronuclei at telophase I were observed. Transmission rates of the N. debneyi chromosomes through the egg and pollen of the addition lines were 8.1 and 10.1%, respectively. The N. debneyi chromosomes in the addition lines occasionally paired with tobacco chromosomes, and therefore, translocation lines with black root rot resistance (2n = 24 II) may be obtained in the self-pollinated progeny by crossing-over. Seventeen RAPD markers were found to be associated with the N. debneyi chromosomes in the addition lines and these should be useful in monitoring further transfer of N. debneyi chromosome fragments into the tobacco genomes.
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