Genome-wide SNP analysis reveals only a moderate level of molecular diversity in castor

Abstract

Castor (Ricinus communis L.) is a highly valuable oilseed crop. The oil and its derivatives are used in manufacturing of several industrial products. It is a monotypic species under Euphorbiaceae family and mostly cross pollinated (aided by wind) though self- pollination does occur. Morphological diversity in castor is highly impressive. However, the status of molecular diversity in castor remains inconclusive. Earlier studies based on molecular markers showed low to moderate level of genetic diversity in castor but those studies had limitations in terms of the number of loci analyzed and the number/representation of the genetic materials used. In this study, we analyzed the molecular diversity in castor by genotyping a panel of 314 representative genotypes (comprised of core germplasm, commercial cultivars and advanced breeding lines) using 5,038 genome-wide SNP loci covering over 85 per cent of the genome. The average polymorphism information content of SNPs was 0.279. The ‘observed heterozygosity’ across the castor genotypes was 0.11, indicating that the genotypes were near homozygous lines. The ‘expected heterozygosity’ (gene diversity) was only 0.351, supporting the moderate level of molecular diversity in castor. The absence of definite population structure in the genotype panel underpinned the possibility of free gene flow. It is surprising that excellent phenotypic diversity in castor was not reflected at the molecular level. One possibility is that most of the phenotypic variations in castor may be due to the epigenetic mechanisms, which need to be explored.