Abstract: The chemical components are the important traits influencing the leaf quality of tobacco. QTLs linked to the chemical components can be used for marker-assisted selection in leaf quality improvement in tobacco. The objective of this study was to identify QTLs linked to several chemical components in the flue-cured tobacco. A population of 137 doubled haploid (DH) lines derived from a cross between two flue-cured tobacco cultivars G-28 and NC2326 was employed to construct the genetic linkage map. Twenty-three new markers were obtained by ISSR and RAPD analysis, and were combined with the previous marker data for the construction of linkage map. A genetic linkage map consisting of 11 ISSR markers and 158 RAPD markers was developed. The map consisted of 27 linkage groups and spanned 2 094.60 cM with an average distance of 15.95 cM between adjacent markers. The data for three chemical components including total sugar (TS), nicotine (NIC) and potassium oxide (KO) were collected from a field experiment conducted in four different environments, and a full-QTL model and the corresponding mapping software were used for the preliminary QTL analysis. Seven additive effect QTLs and nine pairs of epistatic QTLs were detected. The results indicated that epistasis played important roles in the genetic basis of the chemical components in the flue-cured tobacco. For the epistatic QTLs, in which the individual QTL showed no additive effect, it should be efficient to select the QTL combinations rather than the single QTL. Three additive QTLs and three pairs of epistatic QTLs were found to involve in QTL-by-environment interactions (QE): The additive QTL-by-environment interactions were detected for NIC and KO, and the epistatic QTL-by-environment interactions were detected for TS and KO. QTL-by-environment interactions presumably arise from the differential gene expression in various environments and their application in marker-assisted breeding programs would require careful consideration with regard to a particular set of environmental conditions. The present study provides a starting point for detecting QTLs for economically important traits and for understanding the genetic basis of the traits.

Key words: Flue-cure tobacco, Genetic linkage map, Chemical component, QTL analysis, Epistasis, QTL-by-environment interaction