Abstract
This study was conducted to evaluate the potential of strain crossing, transferring seedling salt tolerance into elite cultivars of alfalfa (Medicago sativa L.) without additional selection. Alfalfa cultivars (Mesilla, Moapa 69 and CUF 101) and two donor populations ('AZ-GERM SALT-II' (AZ-GS-II) and AZ-GS-EM) were used in this study. The experiment was conducted during season 2005 at the College of Food and Agriculture Sciences, King Saud University, Experimental Research Station, at Deirab near Riyadh (24oN, 46oE), Saudi Arabia. Six strain crosses were produced between the two donor populations and three alfalfa cultivars. The performance of strain crosses for salt tolerance at germination (250 mM NaCl) was between 7.0 and 52.4% higher than the non-tolerant parental population. Seedling emergence was uniformly high for all populations with non-saline irrigation in the glasshouse (78 to 90%) and no significant differences in emergence percentage were observed between parental or strain-cross populations. The ratio of performance with saline irrigation to that under non-saline conditions, of strain crosses averaged 10.6% greater than that of the non-tolerant population. Relatively little variation in single-plant forage yield was observed among populations in either irrigation regime. With saline irrigation, significant low-parent heterosis for survival (+33.2%) was observed, only for the strain cross whose parents differed significantly in survival (AZ-GS-II X CUF 101). These results indicate that strain crossing could be used to achieve a rapid improvement in seedling emergence under salt stress in alfalfa. Strain crossing did not have a consistent effect on seedling survival or forage yield under salt stress (100 mM NaCl).