Salt Tolerance and K/Na Ratio of Perennial Ryegrass, Tall Fescue, and Orchardgrass Species Under Salinity Stress in Saudi Arabia.

Salinity is a limiting factor for forage productivity in central Saudi Arabia. The aim of this study were to evaluate salt tolerance index (STI) and ratio between Na+ and K+, of a number of introduced cool season grasses species. Four salinity levels of irrigated water were used (control ,4000, 8000 and 2000 ppm NaCl, representing S1, S2, S3, and S4 treatments respectively). Plants were seeded in pots with three replications for each salinity level. Five grass cultivars belonging to four species were established under greenhouse condition at Qassim University Agricultural Research and Experimental Station during the 2012 and 2013 seasons as follows: Perennial ryegrass (Lolium perenne L.cvs Aries(only during 2012 season) and Quartet), endophyte-free tall fescue (Festuca arundinacea Schreb. cv. Fawn), and orchardgrass (Dactylis glomerata L.cv. Tekapo). Rhodes grass (Chloris gayana L.cv. Katambora). Dry weights (g pot-1), Salt tolerance index, and K and Na concentrations in studied grass cultivars were evaluated. The results indicated that dry weights decreased significantly as the salinity level of the irrigation water increased. Rhodes grass produced the highest level of dry weight under the control treatment. However,its dry weight was 30 and 50% lower at 4000 ppm salinity at the two sample cuttings, respectively. At a salinity of 4000 ppm, Aries- perennial ryegrass had the highest dry weight at both sample cuttings. Aries, Fwan and Quartet showed high values of STI. K% and K/Na ratio increased with increasing the salinity level TF/Fwan and PR/Quartet. In the same previous cultivars, Na % decreased with increasing the salinity level of the irrigation water. In contrast, it was found with cultivars RG/ Katambora and OG/ Tekapo. Key words: Cool season grasses, salinity stress, salt tolerance index (STI), K/Na ratio