Genetic diversity assessment, germplasm resource conservation, and utilization in <i>Elymus sibiricus</i> from the margin of Northeast Qinghai-Tibet Plateau based on phenotypes and genotypes

<italic>Elymus sibiricus</italic>, a dominant native grass species on the margin of the Northeast Qinghai-Tibet Plateau (NEQTP) alpine meadows, is crucial for forage production and ecological restoration. However, limited studies on phenotypic and genetic diversity have hampered the protection and utilization of germplasm in <italic>E. sibiricus</italic>. In this study, the dual diversity evaluation based on phenotypes and genotypes was performed on 200 germplasms of 20 <italic>E. sibiricus</italic> populations using 19 phenotypic traits and 14 molecular markers. An abundant polymorphism was observed, with the phenotypic variation coefficient ranging from 2.97% (booting time) to 55.13% (breaking tensile strength) and Nei's genetic diversity index varying from 0.02 (TZ03) to 0.17 (LQ05). Both phenotype differentiation coefficient and molecular analysis of variance showed variation mainly from among populations. Clustering and STRUCTURE results showed that all populations are divided into two groups. A total of 24 loci were determined with a significant relationship to phenotypic traits by Tassel analysis, and the marker Ltc0121 can be used to identify both yield and flowering traits. Altitude distance (r = 0.613, <italic>p</italic> = 0.010) affected genetic diversity rather than geographical distance (r = 0.044, <italic>p</italic> = 0.220) for <italic>E. sibiricus</italic>. Our study evaluated the germplasm of Tianzhu County for the first time. According to the results of dual diversity evaluation, the lowest genetic diversity population TZ03 should be conserved using both <italic>in situ</italic> and <italic>ex situ</italic> approaches. The collection and evaluation of <italic>E. sibiricus</italic> in this study provided a key prerequisite for conservation and utilization in the margin of NEQTP.