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The bentgrasses (Agrostis spp.) are among the most important species to the turfgrass industry. They have complex genomes resulting from polyploidization and high rates of interspecific hybridization. An understanding of species relationships would improve the efficiency of developing improved bentgrass cultivars. To elucidate the evolutionary relationships among Agrostis species, phylogenetic analyses were performed on sequences of two chloroplast-encoded intergenic spacer regions. A 298-bp region of the trnL-trnF intergenic spacer and a 451-bp region of the atpI-atpH intergenic spacer were included in the analyses. A total of 47 Agrostis accessions were included with both cultivated and unimproved material from the National Plant Germplasm System. Of these 47 Agrostis collections, there were 10 unique trnL-trnF haplotypes and eight distinct atpI-atpH haplotypes, indicating a high degree of shared sequence identity within these chloroplast intergenic regions. These findings suggest that the chloroplast genomes of A. canina and A. stolonifera are more closely related to each other than either species is to A. capillaris, incongruent with our previous understanding of genome relationships in the genus. The bentgrasses (Agrostis spp.) are important species to the turfgrass industry because of their ability to form a dense, high-quality turf at low mowing heights. There are between 150 and 200 species of Agrostis (Harvey, 2007), and the evolutionary relationships between species are not clearly understood. Deducing these relationships is complicated by a number of factors. The major turf-type Agrostis species are highly outcrossing and exhibit high rates of heterozygosity (Warnke et al., 1998). Several species are polyploid causing homoeologous loci. Homologous genes often have high levels of sequence identity and may not be informative. Intermediate morphologies exist between taxa making taxonomic classification difficult. Interspecific hybridization is common and these reticulation events are difficult to represent in bifurcating phylograms. Jones (1956a, 1956b, 1956c) described the chromosome pairing behavior during metaphase I of meiosis among Agrostis stolonifera, A. canina, A. capillaris, A. vinealis, and A. gigantea. Agrostis vinealis is an autotetraploidization of A. canina (Jones, 1956a) and these species have the genome designations A1A1A1A1 and A1A1, respectively (Brilman, 2001). The tetraploids A. capillaris (A1A1A2A2) and A. stolonifera (A2A2A3A3) share one sub-genome in common (A2A2) and the hexaploid A. gigantea (A1A1A2A2A3A3) has two sub-genomes in common with both A. capillaris and A. stolonifera (Jones, 1956b, 1956c). The experiments conducted by Jones are among the most comprehensive describing the relationships between these common turf-type Agrostis species. Evidence of Agrostis species relationships based on contemporary molecular marker technologies is lacking. Molecular markers have been used in several studies to explore Agrostis genetic diversity. For example, Vergara and Bughrara (2003) examined 400 polymorphic amplified fragment length polymorphism (AFLP) makers in a set of 40 Agrostis accessions representing 14 species. They reported that A. transcaspica is diploid and based on clustering of AFLP markers, this species may have contributed the A3A3 genome to the evolution of A. stolonifera and A. gigantea. Amundsen and Warnke (2011) explored genetic diversity among 75 Agrostis accessions along with six closely related species based on 1309 miniature invertedrepeat transposable element (MITE) display markers. The modified AFLP technique, MITE display, anchors the amplified products to MITEs. The Agrostis accessions were divided into six clades based on marker clustering (Amundsen and Warnke, 2011). Species relationships can be partially inferred from these Agrostis diversity studies, but there have been no studies designed to specifically explore these relationships. Species relationships can be deduced from nuclear and plastid DNA sequences. Reichman et al. (2006) sequenced the chloroplast matK gene and nuclear internal transcribed spacer (ITS) region from 19 Agrostis and three Polypogon accessions. Phylogenetic analysis of the DNA sequences was used to determine if transgenic A. stolonifera from a controlled area was capable of pollinating wild populations of related species growing at a distance. The individual phylogenies were used to distinguish Agrostis accessions by species. Certain Agrostis species have been included in phylogenies of the Aveneae and Poeae tribes based on DNA sequence data, placing Agrostis species sister to Calamagrostis and Polypogon species within the tribe Aveneae (Döring et al., 2007; Quintanar et al., 2007; Soreng et al., 2007). Inference of Agrostis evolution, a highly outcrossing polyploid, based on ITS or other high copy-repetitive sequence elements, might not provide an accurate depiction of species evolution (Feliner and Rosselló, 2007) and single or low-copy nuclear genes might be more informative (Feliner and Rosselló, 2007; Sang, 2002). One drawback of using low copy genes is that they can be difficult to identify in non-model organisms such as Agrostis. Rotter et al. (2007) sequenced expressed sequence tag DNA libraries of the two Agrostis tetraploid species A. stolonifera and A. capillaris covering 10% of the predicted gene space. This sequencing effort led to the identification of 177 and 161 Oryza Conserved Ortholog Set (COS; Fulton et al., 2002) genes conserved in the A. capillaris and A. stolonifera DNA sequence libraries, respectively. Fulton et al. (2002) describe a reference set of 1025 COS genes that are single or low copy genes and conserved across diverse genomes. Seven of the 161 A. stolonifera and 11 of the 177 A. capillaris Oryza COS gene homologs were found to have conserved sequences in other grasses. These sequences were used in phylogenetic analyses that placed the Agrostis species closer to Festuca arundinacea than to Avena sativa, which is interesting because Agrostis is in the same tribe as A. sativa, whereas F. arundinacea is in the Poeae tribe. Agrostis was placed in the Aveneae tribe based on morphological characteristics and enzyme restriction patterns of chloroplast DNA (Soreng and Davis, 1998; Watson, 1990). The two tribes are closely related (Kellogg, 1998; Soreng et al., 2007) and share many common chloroplast DNA restriction sites (Soreng et al., 1990). Chloroplast sequences would be more informative for deducing Agrostis relationships because chloroplasts are maternally inherited in Agrostis and have simple genomes (Warnke, 2003). Soreng et al. (2007) performed a phylogenetic analysis of the tribe Poeae using morphological characteristics and Received for publication 26 Aug. 2011. Accepted for publication 10 Nov. 2011. To whom reprint requests should be addressed; e-mail kamundsen2@unl.edu. 18 HORTSCIENCE VOL. 47(1) JANUARY 2012 sequence data of three chloroplast-encoded genes, maturase K (matK), NADH dehydrogenase subunit F (ndhF), and ATP synthase beta subunit (atpb). The sequence data for this project are available through the National Center for Biotechnology Information databases and the analysis included the species Agrostis tenerrima Trin., Calamagrostis arundinacea (L.) Roth., C. canadensis (Michx.) P. Beauv., Polypogon monspeliensis, Festuca rubra L., and F. subverticillata (Pers.) E.B. Alexeev. Soreng et al. (2007) found that molecular character data were better than morphological data at describing a well-resolved set of species relationships. Similarly, Döring et al. (2007) sequenced the matK gene from a number of specimens from the Aveneae/ Poeae complex including A. capillaris, C. rivalis (Torges) H. Scholz., C. macrolepis Litv., Apera spica-venti (L.) P. Beauv., P. monspeliensis, Avena sativa L., F. altissima All., and F. gigantean (L.) Vill. Agrostis can hybridize with Polypogon spp. and shares morphological characteristics in common with Apera and Calamagrostis spp. (Harvey, 2007). The results of Döring et al. (2007) were consistent with Soreng et al. (2007) and it is interesting that both phylogenies of chloroplast-encoded gene sequence data placed Agrostis more closely to Avena than Festuca in contrast to the COS phylogenetic analysis performed by Rotter et al. (2007). Different homologous DNA segments from related taxa often have inconsistent evolutionary histories and analyzing the DNA segments separately will often yield trees of differing topologies (McBreen and Lockhart, 2006). These inconsistencies may arise from reticulation events such as horizontal gene transfer, recombination, and hybridization that are not well represented by bifurcating phylogenetic trees (Huson and Bryant, 2006; Huson et al., 2005; Linder and Rieseberg, 2004). A phylogenetic network might be the best representation of the evolution of Agrostis, because a number of Agrostis species are polyploids and thought to have evolved from naturally occurring interspecific hybrids (Casler and Duncan, 2003). The software program SplitsTree4 can render phylogenetic networks from individual gene trees (Huson and Bryant, 2006). Since the 1956 cytological experiments of Jones, there have been a number of advancements for investigating relationships between Agrostis species, particularly with the use of molecular markers, sequence data, and phylogenetic analyses. Genetic relationships in Agrostis have been studied using nuclear markers (Amundsen and Warnke, 2011; Vergara and Bughrara, 2003), but the focus of these studies was to resolve genetic diversity. Agrostis has been included in other phylogenetic studies of the tribe Poeae and Aveneae (Döring et al., 2007; Quintanar et al., 2007; Soreng et al., 2007), but to date, there are no studies focused on resolving evolutionary relationships within Agrostis based on chloroplast sequences. In the present study, the chloroplast encoded trnL-trnF and atpI-atpH intergenic spacer regions were

Agrostis Species Relationships Based on trnL-trnF and atpI-atpH Intergenic Spacer Regions