Comparative responses of two Kentucky bluegrass cultivars to salinity stress

Little information is available concerning physiological responses of Kentucky bluegrass (Poa pratensis L.) (KBG) cultivars to salinity. Growth and physiological responses of 'Limousine' and 'Kenblue' KBG to a range of salinity levels were investigated. Grasses were grown in solution culture and exposed to salinity levels of 2.2, 5.2, 8.2, 11.2, and 14.2 dS m^-1 for 10 wk. Though both cultivars exhibited increased leaf firing with increasing salinity, Limousine exhibited less leaf firing than Kenblue at salinity levels above 5.2 dS m^-1. In addition, salinity levels that caused 25% shoot growth reduction were 3.2 dS m^-1 for Kenblue and 4.7 dS m^-1 for Limousine, indicating that Limousine has better salinity tolerance. Under moderate (8.2 dS m^-1) salinity stress, Limousine produced ∼50% more root growth than Kenblue. Water relations diverged between cultivars at 8.2 and 14.2 dS m^-1, as Limousine had higher leaf water and osmotic potentials, as well as more positive turgor. While glycinebetaine was not detected in either cultivar, proline increased in leaves with increasing salinity, and was higher in Kenblue than Limousine at 8.2, 11.2, and 14.2 dS m^-1. This suggests that compatible solute accumulation is not a salinity tolerance mechanism of KBG, and that proline accumulation is merely an indication of salt injury. Limousine maintained 52% lower shoot Na⁺, 30.4% lower Cl^-, and 52% higher shoot K⁺/Na⁺ ratio than Kenblue at the highest salinity level. These results suggest that salinity tolerance in KBG is largely attributable to maintenance of higher root growth, and more positive turgor, higher K⁺/Na⁺ ratio, and less Cl^- accumulation in shoots. These traits may serve as useful selection criteria in breeding efforts to develop salt tolerant KBG.