1. Introduction Bermudagrass is highly recommended for home lawns as well as golf courses in the southern United States. Bermudagrass has relatively good heat and drought tolerance, and is resistant or tolerant to most diseases and insect pests. However, bermudagrass does not tolerate shade nearly as well as most grasses. It is difficult to maintain quality bermudagrass on shaded areas where limited sunlight is available. Bermudagrass is extremely variable (Taliaferro, 1995). More recently, researchers reported that a large genetic variability existed in a Chinese bermudagrass collection of more than 120 original accessions for adaptive, morphological, and fertility traits (Wu, 2004; Wu et al., 2006). Magnitudes of variances for environment and genotype by environment interactions in the collection are large as well. Molecular markers and ploidy information further indicate substantial genotypic variation within the germplasm pool (Wu, 2004; Wu et al., 2004; Wu et al., 2006). A worldwide bermudagrass collection has been amassed, and is in place for use at the OSU turfgrass breeding program. We believe similar or substantial genetic variation for shade tolerance in bermudagrass exists in the collection. The objectives of this study were to screen bermudagrass selections for their effectiveness in shaded environments and to determine turfgrass characteristics that may be useful for rapid screening of future selections for potential shade tolerance. Materials and Methods A research site was assigned and planted using greenhouse-grown bermudagrass plugs on June 22, 2007 at the Oklahoma State University Turfgrass Research Center, Stillwater, OK. The research site receives mid to late afternoon shade, depending on season, from a dense, mature evergreen canopy on the west side of the site. These conifers also provide root competition and reduce the predominately westerly airflow. Maple trees have been planted along the south side of the site and redbud trees along the east side to increase the duration of vegetative shade. We attempted to increase the duration of shade at the site in 2008 by planting vines along a hoop structure but we had limited success. We had more success with the vines in 2009 and also added a 75% black woven shade cloth above the plots to provide shade in the middle of the day (Photo 1). The study consists of 45 bermudagrass selections and four standards, ‘Celebration’, ‘Patriot’, ‘Tifton 4’, and ‘Tifton 10’. Celebration, Tifton 4, and Tifton 10 were chosen for their potential shade tolerance and Patriot was chosen for its likely poor shade tolerance. The bermudagrass selections were collected primarily from China, Africa, Australia, and other nations. Each bermudagrass was replicated five times on the shade site that is in full sun for about 48% of each day and on an adjacent site that is in full sun for about 90% of each day (Photos 1). The research area was mowed at 3.8cm and irrigated as needed. Visual turf quality (TQ) and Normalized Difference Vegetative Index (NDVI) were assessed every two weeks in 2009 and results are reported for five rating dates from 05 June to 13 Aug 2009 (Table 1). CultivarsShadeSunShade/sun VisualTQ Visual Rank*NDVI**VisualTQVisual RankNDVIDecline*** 1-9=best -- LSD --1-9=best --- LSD ------- % ---- Patriot7.8A0.77178.7A0.7929-2.67 Celebration7.1B0.73007.5BC0.7748-5.78 Tifton47.0BC0.76197.8B0.7795-2.25 C1166.9BC0.75397.4BCD0.7554-0.19 C286.9BCD0.71817.4BCD0.7494-4.17 C1186.7BCD0.71267.0DEFGHIJ0.7648-6.82 Tifton106.6BCDE0.68607.0EFGHIJK0.7191-4.60 C246.6CDE0.69097.3CDE0.7548-8.46 C356.5CDEF0.69967.2CDEFGH0.7318-4.40 C726.5CDEF0.68997.0DEFGHIJ0.7392-6.66 C236.5CDEF0.71397.2CDEFG0.7384-3.30 C346.5CDEF0.69347.4BCD0.7302-5.03 C796.5CDEF0.70427.2CDEFGH0.7461-5.61 C136.4DEFG0.71517.2CDEF0.7674-6.81 C325.6LMN0.65166.4NO0.6864-5.06 C315.4MNO0.62146.5LMNO0.6926-10.28 C825.4MNO0.62336.2OP0.6549-4.82 C745.4NO0.60536.8HIJKLMN0.7003-13.56 C35.4NO0.64696.6KLMNO0.7162-9.67 C1305.1OP0.62385.4Q0.6563-4.95 C835.1OP0.57256.5MNO0.6934-17.43 C844.8PQ0.59795.3Q0.6414-6.78 C694.6Q0.55036.7JKLMN0.6788-18.93 C254.5Q0.56095.8P0.6501-13.72 Table 1.The best ten and worst ten selections including four standards determined by visual quality means collected on five rating dates from 5 June to 13 Aug 2009. Photo 1. A black woven shade cloth (75% light reduction) was added to the shade site in May, 2009. *Based on Fisher's protected least significant difference (P=0.05); means followed by the same letter do not differ significantly **Normalized difference vegetation index ***NDVI in shade compared with NDVI in full sun reported in %; (shade - full sun)/full sun*100 Results and Discussion In 2008, shade stress occurred on the shade site for 12% longer each day than on the sun site. This short duration of shade stress caused an average 4.9% decline in TQ and a 3.4% decline in NDVI in 2008. On May 7, 2009, a black woven shade cloth with 75% light reduction (10ft x 160ft) was installed on a hoop structure to provide longer and more uniform shade for the shade site. Consequently, the shade duration increased from 12% in 2008 to 52% in 2009. Also, it increased decline in TQ from 4.9% in 2008 to 12% in 2009 and a decline in NDVI of 3.4% in 2008 to 7.4% in 2009. The bermudagrass selections differed significantly (P=0.05) in TQ and in NDVI both in full sun and in shade in both 2008 and 2009. The best and worst performing selections ranked by LSD mean separation (P=0.05) of TQ ratings in 2009 are presented in Table 1. Year 2009 results were somewhat different than that of 2008. In 2010, another full growing season will be assessed and experimental units will be screened and selected for future selection of potential shade tolerance. In addition, photosynthesis will be measured from the 10 best selections, 10 worst selections and four standards in May, July, and September with a LI-6400 portable gas exchange system (LI-COR Inc., Lincoln, NE). References Taliaferro, C.M. 1995. Diversity and vulnerability of Bermuda turfgrass species. Crop Sci. 35: 327-332. Wu, Y.Q. 2004. Genetic characterization of Cynodon accessions by morphology, flow cytometry and DNA profiling. Ph.D thesis. Oklahoma State University, Stillwater, OK. Wu, Y.Q., C.M. Taliaferro, G.H. Bai, and M.P. Anderson. 2004. AFLP analysis of Cynodon dactylon (L.) Pers. var. dactylon genetic variation. Genome 47: 689-696. Wu, Y.Q., C.M. Taliaferro, G.H. Bai, D.L. Martin, J.A. Anderson, M.P. Anderson, and R.M. Edwards. 2006. Genetic analyses of Chinese Cynodon accessions by flow cytometry and AFLP markers. Crop Sci. 917-926. Wu, Y.Q., C.M. Taliaferro, D.L. Martin, C.L. Goad, and J.A. Anderson. 2006. Genetic variability and relationships for seed yield and its components in Chinese Cynodon accessions. Field Crop Res. 98: 245-252.