Genetic Diversity and Population Structure of Castor Germplasm within the U.S. Collection

Castor is an important oilseed crop and its oil is inedible but has multiple industrial and pharmaceutical applications. Castor germplasm collection is a useful genetic resource for improving seed quality and developing new cultivars. Seed oil content and fatty acid composition of the entire U.S. castor germplasm collection were previously screened and determined. Significant variability in oil content and fatty acid composition were identified. However, the genetic diversity and population structure of this collection are not well assessed. The missed information can hinder castor breeding and germplasm management programs. Based on the screening results of oil content and fatty acid composition, 574 accessions were selected and genotyped with 22 polymorphic EST-SSR markers. Phylogenetic analysis partitioned accessions into four main clusters and structure analysis revealed four subpopulations. The results from phylogenetic and structure analyses were consistent. Both divergent and redundant accessions were identified in this study. The results obtained here will be useful for choosing accessions as parents to make crosses in breeding programs, prioritizing regeneration of accessions for distribution, and establishing a core collection in germplasm managing programs.