Salinity effects on St. Augustinegrass: A novel system to quantify stress response1

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Abstract
An objective and quantitative batch nutrient culture system was developed to assess responses of St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze) cultivars ''Seville'' (saline tolerant) and ''Floratam'' (saline sensitive) to salt stress. Vessels containing individual grass plugs growing in solution culture were randomized in a walk-in growth chamber. Nutrient solutions were supplemented weekly with NaCl to gradually increase the conductivity over a three week period to treatment levels (2.4 [control], 12.4, 22.4, and 32.4 dS m-1). Plants were sampled at the onset, and at four and eight weeks during the experiment. Cell sap was extracted from grass blades and measured with a vapor pressure osmometer to determine osmolarity and osmotic adjustment. Length and area of sample shoot and root systems and foliage color changes were measured using an adaptation of video image analysis, and dry weight (DW) was measured to determine relative growth rate (RGR). ''Seville'' responded to increasing salt concentration with uniform stepwise increases in cell osmoloarity, whereas ''Floratam'' showed strong depression of cell osmotic potential only in the highest conductivity treatment. At high salt levels, overall shoot development was initially more inhibited for ''Floratam'', although RGR analysis indicated recovery in the susceptible cultivar after long salt stress duration. ''Seville'' reacted to saline stress with increased root length, whereas roots were actually stunted in saline treatments for ''Floratam''. Stress induced an increase in the optical density of grass blades for both cultivars although foliage color was not visibly affected. A positive linear correlation (r = 0.81 - 0.97) was obtained between shoot area as determined by image analysis versus DW measurements. Use of this novel system maximizes assessment of turfgrass stress responses, and quantification of resistance characteristics.