Two systems of genetic control are involved in the quality and level of total alkaloids in tobacco (Nicotianatabacum L.). A single locus controls the conversion of nicotine to nornicotine and two loci control total alkaloid levels. These levels may be further modified by minor genes or quantitative factors. Breeding lines and cultivars of flue-cured tobacco have been developed with varying levels of total alkaloids (nicotine). Levels of nicotine in tobacco range from near zero in cigar strains up to 4.5 % in Burley varieties. Within the collection of N. tabacumgermplasm and Nicotiana species maintained by the Agricultural Research Service of the U.S. Department of Agriculture, total alkaloid levels range from 0.20 % to 7.87 %. Flue-cured lines of tobacco with varying levels of total alkaloids have been developed and characterized. In general the high alkaloid lines had the highest grade indexes. All of the extremely low alkaloid lines were also lower in grade index indicating that total alkaloids do have some relationship with the grade index. The high total alkaloid lines were lower in yield. However, it is believed that the levels of total alkaloids reported do not result from yield variation. N. rustica generally has considerably higher total alkaloid levels, based on percent dry weight, than N. tabacum. With the stabilizing of a low total alkaloid line of N. tabacum (0.20 %) it was feasible to introgress the gene(s) for alkaloid production from N. rustica into N. tabacum. Indications are that more than one gene is responsible for total alkaloid production in this material. Also preliminary indications are that the genes for total alkaloid production in N. rustica may be the same as those in N. tabacum.
