Shade Tolerance in Warm Season Turfgrass.

Turfgrass quality and density can be limited by shade in landscapes, stadiums, and golf courses. Development of new low-light tolerant, polyploid bermudagrass (Cynodon spp.) and zoysiagrass (Zoysia spp.) cultivars can be impeded by quantitative inheritance and the complication of selecting for secondary stresses often found in shaded environments, such as increased disease pressure. The objective was to develop a new screening procedure to predict shade tolerance in field grown plots not exposed to shade, drought, nutrient, or disease stresses by measuring photosynthesis at increasing light intensities in an 81-cm³ enclosed chamber custom built to fit a LI-6400 Portable Photosynthesis System. Each chamber was fitted with a LED light (wavelength range: 2700k to 3500k) and the intensity was manipulated with a 0-60V/0-15A Switch Mode Bench Power Supply, allowing a range of approximately 0 μmol m^-2 s^-1 to 1100 μmol m^-2 s^-1 . A light response curve was created for eight total bermudagrass and zoysiagrass cultivars and experimental hybrids in Tifton, GA during 2016 and 2017. Light compensation points and photosynthetic efficiencies were compared with leaf chlorophyll contents and fluorescence, visual turfgrass ratings, and digital image analysis parameters to begin understanding the relationship of these characteristics. At this time, the light compensation points are most affected by season for both bermudagrasses and zoysiagrasses (P<0.0001), although genotype was significant within summer and spring for zoysiagrass (P<0.0278). Work will continue through 2018 to monitor pertinent environmental conditions such as rainfall, temperature, and humidity to determine if they are affecting measured photosynthetic responses during the different seasons of the year. The ultimate goal is to determine the possibility of predicting the low-light tolerance of different warm-season turfgrasses in full-sun plots based on the physiological responses of historically shade-intolerant cultivars.