Evaluation location: Rhode Island, United States
Screening is conducted in a cool greenhouse during the winter and spring using ambient light. Plants are grown in sand in an edd-flow hydroponics system using modified Hoagland's solution supplemented with sodium cholride. The system is designed to provide uniform salinity stress while minimizing nutrient deficiency, drought, and waterlogging. Each accession is represented by 6 pots, each 7.5 cmx 7.5 cmx 10-15 seeds. Accessions are randomly assigned to flats of 18 pots, which are randomized within the bench. Flats are irrigated with nutrient solution and covered with clear plastic until seeds have germinated. Grasses are maitained at 1" using a reel mower ans scissors. Salt treatment begins after grasses have tillered, 2-3 months after seeding. Four pots for each accession are treated with salt; the 2 control pots recieve Hoagland's solution with no added salt. Salinity is increased by either 1000ppm or 2500 ppm every two weeks, depending on the expected tolerance of the species. Data is collected at the end of each two-week period.
The day before data collection the plants are top-dressed with dry sand to mask any algae growing in the pots. Each flat is photographed from above using a digital camera and a light box. Photoshop is used to crop the image to the edges of the flat and add pink lines marking the edges of the pots. SigmaScan macros are then used to divide the imagie into the 18 individual pots and to calculate the % green cover for each pot. The % cover on each date is adjusted by the % cover for the pot at 0 ppm NaCI, just prior to the beginning of the salt treatment. This compensates for differences in stand caused by variable seed germination. The final green cover is the mean treatment value as percent of the mean control value on that date. Expressing the cover as a percent of the control permits comparison between species that differ in growth habit.