Genetic diversity among and within CIMMYT wheat landrace accessions investigated with SSRs and implications for plant genetic resources management

Many wheat (Triticum aestivum L.) landrace cultivars (LCs) conserved in seed banks are not sufficiently characterized to inspire breeders' interest for their efficient exploitation. Patterns of genetic variation within and among wheat LCs are usually unknown. Two sets of wheat LCs stored in CIMMYT's plant genetic resources center were assessed for genetic diversity by means of 76 (Set 1) and 44 simple sequence repeat (SSR) markers (Set 2). Set 1 included 36 LC accessions originating from different countries, either collected as bulks, composed of a single LC subline, or an unknown collection method. Set 2 consisted of three to 25 sublines of five Mexican and four Turkish LCs already included in Set 1. In a principal coordinate analysis based on modified Rogers' distance (MRD), only three Turkish LC accessions formed a distinct cluster in Set 1. The Mexican accessions clustered together with a Spanish accession and a close relationship between a Chilean and Nigerian accession was observed. In Set 2, gene diversity (H-e) among the Turkish LCs (0.43) was higher than among the Mexican LCs (0.35). Analyses of molecular variance (AMOVA) revealed considerable genetic diversity within Mexican (52.7%) and within Turkish (67.6%) LCs. Pairwise fixation indices (F-ST) were significant, except between two Turkish LCs. Results were discussed in relation to the most suitable collection method of wheat LCs (bulk or individual sublines) as well as to the use of SSRs as a tool for seed bank management.