Genetic diversity and marker-trait associations in a collection of Pak-choi (Brassica rapa L. ssp chinensis Makino) Accessions

Pak-choi (Brassica rapa L. ssp. chinensis Makino) is one of the most important vegetable, especially in southern China. Morphological traits of Pak-choi vary widely, and the genetic basis of these variations is largely undescribed. In this study, we evaluated eighty Pak-choi accessions for genetic diversity based on 29 morphological descriptors and 20 microsatellite (SSR) loci. Our data reveal a high level of diversity in this set of Pak-choi accessions. Euclidean distance was used for cluster analysis. The UPGMA dendrogram grouped the Pak-choi accessions into five major clusters based on morphological characteristics. As expected, similar morphological characteristics grouped together in cluster branches. Further, population structure was explored to identify subpopulations based on allele frequency. Five groups were identified, and showed considerable correlation with the morphological clusters. Associations between SSR markers and agronomic traits were further investigated using a non-parametric Kruskal-Wallis K-test and six additional parametric models. Significant associations were found between 18 SSR loci and 28 morphological traits. This study provides evidence that marker-trait associations can be validated in segregating populations and exploited through marker-assisted selection.