Association Mapping of Agronomic Traits in Oriental Tobacco (Nicotiana tabacum L.) Genotypes

Tobacco (Nicotiana tabacum L.) is one of valuable agricultural and industrial crops. Studying most important traits of tobacco is difficult because of quantitative nature that are controlled by multiple genes and affected by environmental factors. Among various methods for the study of quantitative traits, association mapping which utilize phenotypic and DNA markers information is one of the effective methods for this purpose. In this study, the phenotypic variability of 100 oriental type of tobacco genotypes were evaluated using 10 × 10 simple lattice design with two replications at Urmia Tobacco Research Center. Several agronomic traits including plant height (PH), stem diameter (SD), number of days to 50% flowering (D50F), number of leaves (NL), leaf length (LL), leaf width (LW), fresh leaf yield per plot (FLYP), and dry leaf yield per plot (DLYP) were measured. Also, fingerprinting of 90 out of 100 genotypes was done by using 26 SSR primer pairs. Analysis of population structure of studied germplasm using Structure software classified the association panel into 3 sub-populations. Linkage disequilibrium and analysis of association between markers and traits were performed using TASSEL 2.1 software. The results related to linkage disequilibrium revealed that r2 values ranged from 0.00001 to 0.267 with mean r2 value of 0.027 and also, value of D´ ranged from 0.0065 to 1 with mean D´ value of 0.242. Using association mapping based on GLM and MLM models, 16 and 10 loci were identified which possessed significant relationship with factors controlling agronomical traits. In this study, marker PT30159 was common for number of leaves, plant height and days to 50% flowering traits, marker PT30046 was common for leaf length and stem diameter and marker PT30292 was common for stem diameter and days to 50% flowering traits. Common markers are important and effective in plant breeding activities.