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This study was conducted to assess genetic diversity among the 32 tall fescue half-sib families using a randomized complete block design (RCBD) experiment in the four replicates. Based on analysis of variance, significant differences were observed among studied genotypes at the probability of 1% for plant height, canopy diameter, days to heading, days to pollination, crown diameter, fresh forage yield, dry forage yield, number of stem and seed yield in first harvest and in canopy diameter, crown diameter, fresh forage yield and dry forage yield in second harvest. Based on the results of mean comparisons, highest dry forage yield in the first harvest was obtained in genotype 32 by 758.5 grams. Principal component analysis by considering eigenvalues greater than one, caused to introduction of three components which determined 80.5% of the variation among the samples. In cluster analysis, the greatest of distinction between the groups was achieved with three clusters, and by cutting the dendrogram genotypes in three groups. According to the results, the third cluster was superior to other two clusters in terms of most traits. The genotypes of third cluster, according to the value of this cluster in terms of forage yield and seed yield will be of particular importance in breeding programs. In the breeding of cross-pollinated forage crops, success in selection depends on creating diversity by genetic recombination and achievement of heterosis. Due to the distance between groups 1 and 3, probably the most successful crosses will be achieved among genotypes of these two groups.

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Tall fescue is an out-crossing allohexaploid grass species extensively used for forage and turf worldwide. Cultivars of outbreeding forage grasses such as tall fescue are usually synthetic populations derived from intercrossing several selected parents using the polycross method. In this study, the application of AFLP molecular markers to optimize genetic diversity in a polycross breeding program of tall fescue was evaluated. For both phenotypic characters and AFLP molecular markers, two polycrosses of six parental plants with contrasting levels of genetic diversity were composed. A fifth polycross population was composed using six genotypes with the highest general combining ability. The results of this study showed that marker assistant parental selection produced superior progenies, indicating that selection based on molecular marker diversity may be an appropriate means to improve first generation progenies of tall fescue. This may be mainly useful in large breeding programs because the identification of diversity based on phenotypic traits is time consuming and may be influenced by environmental effects.