Forage plants and turfgrasses are economically very important. Prennial ryegrass ( Lolium perenne ) from Poacea family is one of the most important turfgrasses in the world which is found as a range plant in Iran. This genus is naturally cross pollinated with a high degree of gametophytic self incompatibility. Therefore, seed production through self-pollination could have a plenty of breeding and economic benefits. Perennial ryegrass has symbiotic relationship with endophyte fungi from the species Epichloe Festuca . The fungus has many positive effects on the host plant. Therefore, this study was performed to examine the effect of endophyte on seed production via self-pollination and to assess the possible inbreeding depression from self-pollination in Iranian populations of Lolium perenne obtained via self and open pollination. This study was done in two years during 2014-2015 in research farm of Isfahan University of Technology located at Lavark, Isfahan. Genetic materials included 16 populations infected with endophytic fungi (E+) and 4 non-infected populations (E-) accompanied with two control genotypes planted according to a randomized complete block design with three replications. Results of analysis of variance in the first and second years showed that population effect was significant for most of the traits indicating the importance of plant genotype in expression of the traits. The effect of endophyte was significant for some traits including heading date, the number of panicles per plant, the percentage of erected panicles, and the number of seeds in panicle, 1000-seed weight and seed yield per plant. In evaluation of inbreeding depression, it was shown that endophyte infected plants had superiority over endophyte free ones regarding all the traits excluding plant fresh and dry weights and 1000-seed weight. It means that endophyte decreased inbreeding depression. In principle component analysis, populations were divided into 3 groups in the first year and the two first components could justify 51.8% of variance among the treatments but the separation could not be interpreted. In the second year, populations were separated into 4 groups so that E+ and E- populations were divided and about 56% of the variance among the treatments was justified by the two components. The result of cluster analysis in two years confirmed the results of principle component analysis. In the second year, populations were assorted into 4 groups so that all Iranian endophyte free populations were placed in the third group. The first group could be used as turf based on the plant characteristics, in the second group, plants had intermediate characteristics between turf and forage, the third group was suitable for forage production and the forth group which included two populations are suggested for seed production or utilization in polycrosses. Generally, endophytic fungus improved many characteristics of Iranian ryegrass as some of Iranian populations were competitive with control genotypes even in self-pollinated populations. These effects improved turf and forage characteristics but decreased seed yield except for some populations. Therefore, the prerequisite for production of seeds through self-pollination in symbiotic plants is appropriate interaction between plant and the fungus. The populations of S10 and S9 with production of the highest seed yield via selfing may show an example of suitable interaction between the fungus and plant and they might be suggested for either forage production or as turf. Otherwise, endophyte free populations of ryegrass are preferred since they have higher seed yield. Keywords: Perennial rygrass, Endophytic fungi, Selfing, Cross pollination, Self incompatibility, Inbreeding depression.