Enhanced polycross breeding of tall fescue through marker-based paternity identification and estimation of combining ability

Abstract

Half-sib (HS) mating is the most important breeding method of open-pollinated sexual forage grasses such as tall fescue. Progeny testing procedures of half-sib families can only measure general combining ability (GCA) due to the unknown pollen donor. In tall fescue, genetic studies using HS mating and application of molecular markers for paternity identification in polycross progenies are so far limited. In this study, 960 genotypes from sixteen half-sib families of tall fescue derived from polycrosses, along with their corresponding parental genotypes were evaluated for agro-morphological traits in the field during 2016 and 2017. Genetic diversity of the parental genotypes was assessed using twenty EST-SSR markers and then a minimal set of primers was used to identify the most likely male parent in the polycross progenies. Considerable genetic variation was observed among the parental genotypes based on both morphological and molecular assessments. Moderate to high estimates of narrow sense heritability (0.53–0.84) for morphological traits indicated that phenotypic selection can be successful to achieve genetic progress. The EST-SSR markers allowed to identify a unique paternal parent in 177 of the offspring which were divided into 66 full-sib families. The number of genotypes per full-sib family varied from 1 to 11. Marker data used to identify full-sib families, estimate specific combining ability (SCA), and select siblings based on the genetic value of both parents. No clear association was found between GCA of parents and the corresponding SCA for forage yield, indicating that both additive and dominant gene actions may play a role in the genetic control of this trait. The obtained results highlighted the importance of marker-based paternity identification to increase gain from selection in polycross breeding programs of tall fescue.