Abstract: Abstract The study was conducted to investigate the effect of selecting parents of Eyan1 for nicotine conversion and to compare the effects on reducing converters in improved hybrids, LC-1 and LC-2 with the regular hybrid, which had high proportion of converters in the population. The results showed that through systemic selections for non-converters in the parent lines, the converters and the percent nicotine conversion were reduced greatly. Through 3generation selections, the proportion of converters in the population of B21 reduced to 0.0%to 0.5% from 70.7% in the original population, and for B37, reduced also to the same proportion from 10.9%. The proportions of total converters in the two improved hybrids were 5.0% and 11.6%, respectively, 9 and 4 times lower than the regular hybrid which had the proportion of 45.0%. The percent nicotine conversions of the two improved hybrids in the bulk samples were 2.14% and 3.13%, respectively, 4 and 2.4 times lower than the contract which had the number of 10.65%. The total TSNA contents in the two improved hybrids decreased 86.7% and 102.6% compared with regular hybrid, and the difference was mainly caused by NNN reduction, the percent decreases were 186.9% and 155.5%, respectively. Improved hybrids had better tobacco flavor quality than the regular bybrid, with increased burley style, enhanced aroma quality and quantity, and decreased offensive odor. Therefore the improved hybrids had high value of utilization in burley tobacco production.

Key words: improvement , tobacco, alkaloid, nicotine, nornicotine, nicotine conversion rate, converter, hybrid, parents