Genomic characterization of pre-Green Revolution wheat landraces from the Nepalese and Bhutanese Himalayas reveals geographically structured diversity.

Wheat (Triticum aestivum L.) landraces collected before the widespread regional adoption of Green Revolution cultivars provide a historical record of locally maintained germplasm. We characterized a panel of 202 accessions collected from Nepal and Bhutan between 1952 and 1958. Genotyping by Random Amplicon Sequencing-Direct yielded 30,228 high-quality markers; removing 38 close genetic duplicates produced a nonredundant panel of 164 accessions. We investigated genetic diversity, linkage disequilibrium, population structure, and spatial variation in effective migration, compared the panel with 187 analyzed accessions from a global hexaploid wheat core collection, and evaluated four agro-morphological traits in a common environment. We identified eight geographically patterned genetic groups and 28 admixed accessions. All four traits differed significantly among groups, and plant height, days to heading, and days to flowering correlated with collection-site altitude. The global core panel had higher overall marker-based diversity. Nevertheless, Group 7, the Bhutan-enriched Group 8, and several transitional accessions occupied regions of genetic space with limited representation in that panel. This historical collection therefore complements global core resources by providing fine-scale regional diversity and a basis for accession selection for multi-environment phenotyping, allele discovery, and pre-breeding.