Identification and mapping of nucleotide binding site-leucine-rich repeat resistance gene analogs in bermudagrass.

Thirty-one partial bermudagrass (Cynodon spp.) disease-resistance gene analogs (BRGA) were cloned and sequenced from diploid, triploid, tetraploid, and hexaploid bermudagrass using degenerate primers to target the nucleotide binding site (NBS) of the NBS-leucine-rich repeat (LRR) resistance gene family. Alignment of deduced amino acid sequences revealed that the conserved motifs of the NBS are present and all sequences have nonDrosophila melanogaster Toll and mammalian interleukin-l receptor (TIR) motifs. Using a neighbor-joining algorithm, a dendrogram was created and nine groups of deduced amino acid sequences from bermudagrass could be identified from those sequences that span the NBS. Four BRGA markers and 15 bermudagrass expressed sequence tags (ESTs) with similarity to resistance genes or resistance gene analogs were placed on a bermudagrass genetic map. Multiple BRGA and EST markers mapped on T89linkage groups la and Sa and clusters were seen on T89 19 and two linkage groups previously unidentified. In addition, three primers made from BRGA groups and ESTs with similarity to NBS-LRR resistance genes amplify NBS-LRR analogs in zoysiagrass (Zoysia japonica or Z. matrella) or seashore paspalum (Paspalum vaginatum). This gives evidence of conservation of NBS-LRR analogs among the subfamilies Chloridoideae and Panicoideae. Once disease resistance genes are identified, these BRGA and EST markers may be useful in marker-assisted selection for the improvement of disease resistance in bermudagrass. Bermudagrass is a C4 perennial grass used widely for lawns, sports fields, parks, golf courses, and pastures, and to prevent soil erosion in most of the warmer environments across the world. Common bermudagrass (Cynodon dactylon, 2n = 4x = 36) can be a serious weed that is difficult to eradicate because of stolons that readily root at the nodes, deep rhizomes, and seed production (Webster et aI., 2004). Another type of bermudagrass, african bermudagrass (Cynodon transvaalensis, 2n = 2x = 18), is a very fine-textured grass that has poor wear and pest tolerance compared with the improved triploid hybrids (Hanna, 1986; Wiecko, 2007). Improvement of bermudagrass has occurred by selection for turfgrass adaptability and aesthetic traits from common bermudagrass such as 'Tiflawn' (Hein, 1953) and the release of sterile triploid hybrids (2n = 3x = 27) between C. transvaalensis and C. dactylon such as 'Tifgreen' and 'Tifdwarf (Burton, 1966; Hein, 1961). Most Received for publication 30 Nov. 2009. Accepted for publication 22 Jan. 2010. We thank Mrs. Jacolyn Merriman for technical assistance, Drs. Wayne Hanna and Earl Elsner for plant material, and Amnon Levi for use of some degenerate primers. The mention oftrade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply the recommendation or endorsement by the U.S. Department of Agriculture. 'Corresponding author. E-mail: Karen.Han·is@ars.usda. gov. 74 new releases are vegetatively propagated triploid hybrids that are more pest resistant, make a denser turf, tolerate close mowing, have fewer seedheads, and are more uniform than common bermudagrass (Webster et aI., 2003). Bermudagrass is susceptible to a wide range of fungi (Pratt, 2003), nematodes (Giblin-Davis et aI., 1992), and insects (Chang et aI., 1985; Reinert and Busey, 2001; Shortman et aI., 2002), although few are considered to be serious issues when properly managed. The major fungal diseases of bermudagrass include spring dead spot caused by Ophiosphaerella herpotricha, 0. korrae, and 0. narmari, brown patch caused by Rhizoctonia spp. , and dollar spot caused by Sclerotinia homoeocarpa (Baird et aI., 1998; Taliaferro, 2003). Serious insect pests include southern and tawny mole crickets (Scaptericus acletus and S. vicinus), tropical sod webworm (Herpetogramma phaeopteralis), and fall armyworm (Spodoptera frugiperdai (Taliaferro, 2003). Nematodes, including sting (Belonolaimus spp.), lance (Hoplolaimus spp.), root-knot (Meloidogyne spp.), and spiral (Helicotylenchus spp.), also may cause serious injury to bermudagrass (Crow, 2002; White and Dickens, 1984). Widespread mono culture of only a few cultivars such as Tifdwarf and Tifway could cause new resistant strains of diseases and pests to develop by selection pressure (Taliaferro, 1995). To date, the development of cultivars with resistance to 1. AMER. Soc. HORT. SCI. 135(1):74-82.2010.