Investigation of evolutionary relationships and history of RYE (SECALE SP.) in Turkey with global comparisons

Abstract

Genus Secale is a small but important genus that includes cultivated rye. The genus is quite heterogeneous with annual, perennial, self-incompatible and self-compatible species and subspecies. Taxonomy of the genus is still controversial due to disagreement about the delimitation of species and intraspecific taxa, out-crossing nature of many species and lack of hybridization barriers between species and subspecies. A collection of 727 individual genotypes derived from 142 different accessions of the genus Secale representing S. cereale, S. vavilovii, S. strictum and Secale sylvestre were investigated from different eco-geographical areas of the world with a concentrated focus on Turkey and the Middle East. The accessions were screened with a set of seven polymorphic SSR loci, a chloroplast SNP, and a nuclear SNP, in order to understand the population structure and estimate distribution of genetic variation within the genus, and infer the genetic bases of current taxonomy and phylogeny. The results showed high levels of genetic diversity among cultivated rye populations from different geographical origins. Among these regions, the Middle East showed the highest genetic diversity, supporting the idea of the area being the center of origin for cultivated rye. The hierarchical population structure indicated that perennial S. strictum subspecies are genetically divergent from annual forms of the genus. A strong geographical structuring was observed within annual taxa. Existence of two distinct clusters was observed, one corresponding to Asia, and second covering samples from outside of Asia. Lack of structuring corresponding to taxonomical delimitations among annual taxa was explained by insufficient time for the evolution of isolation mechanisms or barriers between cultivated rye and its wild and weedy relatives, and consequent introgression between these taxa. Although this extensive introgression between taxa might blot out the phylogenetic signal, markers developed using nextgeneration sequencing might provide better resolution for understanding the exact phylogenetic relationships within the genus Secale.