Evaluating canopy morphology as predictive indicators of shade tolerance in three warm-season turfgrass species

Improving shade tolerance is critical for development of new turfgrass cultivars in the United States. Comparing turfgrass coverage under reduced sun exposure is a popular and effective method for determining shade tolerance, but requires years to evaluate. The objectives were to (i) compare phenotypical differences of experimental genotypes and cultivars of bermudagrass (Cynodon spp.), St. Augustinegrass (Stenotaphrum secundatum), and zoysiagrass (Zoysia spp.) grown under 73% shade and (ii) identify whether genetic improvement for shade adaptation was made in these species. This 3-year study conducted in Tifton, GA, found phenotypic differences among genotypes within species for turfgrass coverage when exposed to 73% shade. The experimental bermudagrass, 11-T-56, possessed the superior combination of high green turfgrass coverage, low canopy height, and season long dark green color under shade. Experimental genotypes in St. Augustinegrass exhibited genetic improvement compared to commercially available cultivars; however, these genotypes should be examined under more intense shade to elicit differences before further selection. Performance of experimental zoysiagrass genotypes from several turfgrass breeding programs did not indicate significant improvement in the shade persistence within Zoysia spp. There appears to be genetic differences in the speed at which newer zoysiagrasses can initially spread by rhizomes and stolons when grown under shade. Further research should be conducted to determine if juvenile growth is an indicator of shade tolerance under natural tree shade or structures. Overall, results indicated that canopy heights cannot be used to directly predict shade tolerance but can be used to identify turfgrasses with reduced mowing frequency requirements.