Developmental Responses of St. Augustinegrass Cultivars and Experimental Lines in Shade.

Shade is one of the most widespread challenges in turfgrass management, and little information is available regarding intraspecific differences in shade tolerance among St. Augustinegrass cultivars.  Greenhouse studies were conducted in 2011 and 2012 to evaluate developmental responses among cultivars and experimental lines of St. Augustinegrass to increasing shade intensity.  Included in the evaluations were cultivars ‘Raleigh’, ‘Palmetto’, ‘Captiva’, ‘Delmar’, ‘Amerishade’, as well as advance experimental lines ‘DALSA 0406’, ‘DALSA 0605’, ‘DALSA 5389’, ‘DALSA 5732-6’, ‘DALSA 5395-4’.   Turfgrass sod plugs (10 cm diameter x 5 cm deep) were transplanted into 25 cm diameter x 12.5 cm deep pots and grown for 10 weeks under full sun (0% shade), moderate (60%), or heavy (80%) density-neutral shade.  To characterize the shade responses of the entries, vertical growth rates, lateral spread, and change in percent green cover were measured over five 2-week intervals.  Root growth, chlorophyll, and total nonstructural carbohydrates were also determined.  Considerable variation existed between the entries with regard to all parameters.  In heavy shade, ‘Amerishade’, ‘Delmar’, and ‘DALSA 5389’ maintained much more decumbent growth relative to other entries.  With the exception of ‘DALSA 5389’, all entries showed decline in percent green cover in heavy shade over the 10-weeks.  ‘DALSA 0406’ exhibited improved root growth relative to all other entries in both shade treatments.