2012 Annual Report 1a.Objectives (from AD-416): Characterize the physiological mechanism(s) of salinity tolerance in selected alfalfa lines by identifying how the plants cope with saline soils. 1b.Approach (from AD-416): Three major salinity tolerance mechanisms in plants have been identified; salt secretion, exclusion and sequestration. It is hypothesized that salt-tolerant alfalfa may utilize one or more of these mechanisms. Detailed physiological analysis will be conducted to determine which mechanism(s) confer salinity tolerance to experimental lines of alfalfa. Alfalfas with contrasting salinity tolerance will be analyzed for salt gland formation, deposit of salt crystal on tissue surface, salt contents in different tissues and distribution of salt at the cellular and sub-cellular level. In addition, assays for oxidative stress and detoxification will also be performed. 3.Progress Report: The main objective of this project is to determine the physiological mechanisms of salt tolerant alfalfa germplasm. During FY-12, four populations of alfalfas selected for salt tolerance in the greenhouse were the subject of this research. In anticipation of conducting the work field trials were established in the spring of 2009 near Castle Dale, Utah under saline conditions and near Milville, Utah under non-saline conditions. The first year morphological data was used to select plants for additional physiological and molecular characterization. During FY-2012: Physiological characterizations of two of the salt-tolerant selected lines were conducted. Based on stem length and leaf number measurement both lines demonstrated improved growth under salt treatment compared to their parental lines. This improved growth is associated with a greater accumulation of chlorophyll in the selection lines as indicated by chlorophyll content index measurements. The selected lines also showed improved capability of maintaining water status (relative water content). The two lines, however, showed a difference in total electrolyte accumulation in shoots during salt treatment. One line showed little accumulation of electrolyte while the parental lines showed a significant increase in electrolyte after salt treatment. The second line showed the same degree of electrolyte accumulation compared to its parental line under salt stress. These results provide physiological basis to support the improved salt tolerance in these selected lines. Among the parameters assessed, change in leaf number appeared to be the most responsive to salt treatment. While the two selected lines share some of the physiological features during the response to salt treatment, the results also suggest the two selection lines may have adapted different mechanisms in salt tolerance.