A haplotype-resolved genome assembly of hexaploid Kentucky-31 tall fescue (Lolium arundinaceum).

Hexaploid tall fescue is a widely adapted forage and turf grass with three synonyms in botanical nomenclature. It is one of the most drought-tolerant cool-season forage and turf species and can host Neotyphodium endophytes that can further affect physiological traits. The cultivated variety "Kentucky-31" (K31) was one of the original tall fescue varieties, yet it still has a large presence in the current market. We generated a haplotype-aware assembly of K31 tall fescue along with its chloroplast genome, with structural and functional gene annotation. Each haplotype assembly was approximately 7.1Gb. The three sub-genomes within each haplotype assembly were discernible and syntenic, with the Festuca pratensis (P) sub-genome intermediate in size between the two sub-genomes from F. glaucescens (G1 and G2). Interspersed repeat levels were high in the assemblies, with long terminal repeats alone comprising over 50% of the genome space. With an interest in testing for K31 as a variety, 15 seed sources of K31 were obtained from forage and turf industry sources, and their genetic relationship was tested with pairwise PhiST statistics from over 3,400 SNP markers that mapped across the genome. All but four seed sources coalesced into a group that differed from turf-type cultivated variety checks; three were broad-based and did not differ from any other entry; and K31-4 was genetically differentiated from all other K31 sources. These results provide a chromosome-scale and haplotype-aware tall fescue genome assembly for mapping and functional genomic studies.