Evaluation of nuclear DNA content and heterochromatin changes in anther-derived dihaploids of tobacco (Nicotiana tabacum) cv. Coker 139

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Abstract
Nuclear DNA contents of a conventionally inbred flue-cured tobacco (Nicotiana tabacum L.) cultivar. 'Coker 139,' and two selected, doubled haploid (dihaploid) lines developed from it by anther culture and colchicine chromosome doubling were compared. The dihaploid lines had previously been shown to be lower yielding and agronomically inferior to the parental cultivar. Nuclei of leaf and root cells of the dihaploids possessed significantly higher amounts of DNA than the parental cultivar, although chromosome numbers (2n = 48) had not changed. Mean nuclear DNA content of the dihaploid lines was 10.62 pg, while nuclei of the parental cultivar contained 9.32 pg. The anther-culture process and (or) the nature of vegetative nuclei of pollen grains from which haploid plants originate have been suggested as possible contributing factors to higher DNA values. An average 12% increase in heterochromatin (condensed chromatin) in dihaploids, and significant differences in thermal denaturation of parental and dihaploid DNAs, suggest an amplification of DNA sequences during dihaploid formation.