Plant germplasm is an important gene resource for plant breeding and genetic improvement of traits . Core collection , as a representative subset of germplasm , provides an effective entry to investigate genetic diversity and screen potential breeding material . Most agronomic traits of tobacco often exhibit strong genetic variation which can be decomposed into genotypic and genotype × environment interaction variations . A tobacco collection of 805 accessions were evaluated in two locations , Fuquan and Jinsha City of Guizhou Province , China . The genetic variations of 12 agronomic traits were analyzed and the genotypic values of each accession were predicted by a mixed linear model approach . Significant genotypic variations were detected for 11 traits , as well as genotype × environment interaction for 10 traits . Based on the predicted genotypic values , the combination strategies of sampling and clustering methods in the procedure of stepwise clustering for constructing core collection were screened in terms of magnitude of genetic variation captured by sampled subsets . Finally , the subset ( S1C3_10) , sampled by a centroid method combined with preferred sampling at 10% proportion , was determined to be a core collection of the tobacco germplasm . The representative and validation of the core collection was examined visually by the accession distribution pattern in the plot established by first two principal components , as well as by the correlation coefficients in terms of magnitude and significance between the core and the initial collections . The results showed that the initial collection was well represented by the core collection , and some potential breeding materials for high yield breeding program of tobacco , such as Y 177 and Y178 , were included in the core collection . In sum , the constructed core collection will facilitate tobacco breeder to access to whole resources and promote the utilization of genetic diversity in future breeding program of tobacco in China .

Analysis of genetic main effects and genotype x environment interaction effects for total sugar and reducing sugar of flue-cured tobacco were conducted at two locations and diallel cross by using the additive, dominance and additive x additive model. Unconditional and conditional analyses were employed to investigate the developing behavior of quantitative traits and uncover the genetic mechanisms of flue-cured tobacco. Total and reducing sugars were greatly affected by genotype x environment interaction effect rather than genetic main effect, and gene intermittently expressed and exhibited different genetic mode in different growth stages. It was suggested that genetic imporvement for total sugars of flue-cured tobacco could be achieved by selection of pure lines in the period of Gs1118 to Gs1121 in early generations and by selection of heterosis in the period of Gs1112 to Gs1121 in advanced generations under specific environments. (C) 2012 Friends Science Publishers