Genetic Diversity and Population Structure of Brassica napus

Industrial rapeseed (Brassica napus L.) is an annual crop whose seeds produce high levels of erucic acid. The non-edible oil can be used as a sustainable source of hydrotreated renewable jet (HRJ) fuel, motivating strategies to increase the domestic production of industrial rapeseed oil. In part, increased production can be achieved by introducing rapeseed as a rotation crop in the western U.S. non-irrigated wheat production system. However, this requires the development of high yielding, locally adapted rapeseed varieties that are compatible with the HRJ fuel conversion processes. In that light, we are constructing a translational genomics platform to support the molecular breeding of improved winter and spring type industrial varieties. Nearly 900 rapeseed lines that cover a wide geographic origin were assessed for growth habit and scored with a low-density SNP genotyping array. The evaluation of growth habit resulted in the classification of the 870 rapeseed lines as 644 and 226 winter and spring types, respectively. The analysis of the SNP markers by multi-dimensional scaling revealed three distinct clusters, splitting accessions according to their growth habit. One cluster is mainly constituted by spring accessions, the other two clusters are represented by winter types, with European and Asian accessions clustering separately. With this improved understanding of the levels and structure of genetic diversity among these lines, we have initiated high-density SNP genotyping in combination with genome-wide association studies of agronomic and oil quality traits to identify alleles that can be exploited for the rapid development of improved industrial rapeseed breeding lines.