The current study was carried out to access the genetic diversity of eight ryegrass (Lolium rigidum) populations using Microsatellite (SSR) markers. Ryegrass seeds were used from 8 different regions (seven regions in Saudi Arabia i.e. Wadi Aldawaseir, Tabuk, Qassim, Hail, Aljouf, Harad, and Aldawadmi and sensitive to herbicide variety from Syngenta company, England). Four samples from four heavily infested fields were selected making a total of 32 samples. Field trial was conducted in RCBD with three replications. Field performance results showed highly significant differences among the studied 32 genotypes for all studied traits. The results indicated the existence of considerable amount of genetic variations among lolium genotypes. Thirty one SSR markers derived from genomic and EST microsatellites were tested. The results showed that 23 SSR markers (74.19%), were polymorphic and eight (25.81%), showed monomorphic patterns. The number of alleles detected per primer ranged from one in monomorphic primers to 5 alleles in LT C SSR1. The tested primers successfully amplified 1434 bands across eight populations, with average of 46.26 fragments/primer. The polymorphism Information content (PIC) values ranged from 0.11 to 0.76 for primers LT EST-SSR5 and LT C SSR1, respectively. The clustering of the 32 samples representing eight populations based on UPGMA was largely based on location and herbicide tolerance level. Most of studied populations tended to cluster the four representing samples together. Also, the tolerant populations were separated from sensitive ones. The results illustrate the power of SSR markers in detecting the molecular diversity and could be applied to differentiate tolerant from sensitive populations of ryegrass.
