Assessment of Genetic Diversity and Population Structure in a Global Reference Collection of 531 Accessions of Carthamus tinctorius L. (Safflower) Using AFLP Markers

Carthamus tinctorius L. (safflower) is an important oilseed crop that is cultivated in several countries. The present study investigates the genetic diversity and population structure of 531 safflower accessions from 43 countries representing all safflower growing regions of the world. Diversity analysis was performed using ten informative EcoRI/MseI amplified fragment length polymorphism primer pairs that were identified by screening 150 primer combinations. The selected primer pairs generated 381 fragments of which 157 were polymorphic among the analyzed accessions. The genetic diversity indices obtained for the entire collection (I = 0.4536, H = 0.2955) indicated high levels of molecular variability. The distance-based, neighbor-joining method classified the accessions into six clusters with internal subgroupings that were in consonance with 19 clusters obtained using Bayesian model-based BAPS analysis. Clusters obtained through STRUCTURE analysis (at K = 4) could not be correlated with their geographically diverse origins, while BAPS analysis (at K = 19) revealed geographical delineation with low admixture levels among most of the studied accessions. Accessions from Far East and Egypt clustered in distinct groups, indicating conserved nature of their gene pools. The Near East and Iran-Afghanistan regions were collectively found to harbor maximum diversity in accordance with earlier reports. Accessions from the Indian subcontinent showed substantial diversity that was previously undetected. The American accessions showed low molecular variability in contrast to earlier studies. Genetic sub-structuring within gene pools and inter-relationships between accessions belonging to different regional pools was also observed. To the best of our knowledge, this is the first comprehensive study of existing genetic variability in a large collection of safflower germplasm with a global distribution, which provides a more accurate representation of genetic structuring in the crop. This information will facilitate selection of elite genotypes for broadening the genetic base of various breeding programs in safflower.