Project Number: 5428-21000-014-08
Project Type: Reimbursable

Start Date: Nov 01, 2009
End Date: Feb 28, 2014

Objective:
Many agricultural lands in the Western U.S. are composed of soil with high concentrations of salt. In some instances, irrigation contributes to additional salinity. High salinity levels are detrimental to plant survival and production, especially under limited water conditions. Soil salinity is a long term problem and can be addressed with the development of crops that can tolerate high salt levels. Alfalfa, which is an important forage crop in many western States, lacks tolerance to salty soils. Four salt tolerant experimental populations of alfalfa have been developed through selection using a greenhouse protocol to survive salt concentrations up to an electrial conductivity of 18 dc m-1. The agronomic performance testing is incomplete, and the physiological mechanism and underlying molecular basis of salt tolerance of these populations are unknown. The objectives of this proposal are to 1) evaluate agronomic performance of four experimental salt-tolerant alfalfa populations in irrigated saline soil; 2) identify the physiological mechanism of salinity tolerance in these populations, and 3) identify genes and expression patterns associated with salt tolerance.

Approach:
Objective 1: Evaluate agronomic performance of four experimental salt-tolerant alfalfa populations in irrigated saline soils. Approaches: Four salt tolerant populations have previously been developed in CoPD (Dr. Peel's) lab. We will evaluate these experimental salt tolerant alfalfa populations in field locations with high salinity to determine relative forage production, fall dormancy, flowering date, seed production, forage quality and overall plant morphology of these lines with respect to currently available commercial varieties. We hypothesize that alfalfa genotyes will be identified from among the four populations that would meet commercial standards for forage production under saline conditions. Objective 2: Identify the physiological mechanism of salinity tolerance. Approaches: Three major salinity tolerance mechanisms in plants have been identified, salt secretion, exclusion and sequestration. We hypothesize that salt-tolerant alfalfa may utilize one or more of these mechanisms. We will conduct detailed physiological analysis to determine which mechanism(s) confer salinity tolerance to the experimental lines. We will compare lines contrast in salinity tolerance for salt gland formation, deposit of salt crystal on tissue surface, salt contents in different tissues and distribution of salt at the cellular and subcellular level. In addition, assays for oxidative stress and detoxification will also be performed. The findings from these studies will be critical to identify genes and proteins that define molecular basis of salinity tolerance in the experimental alfalfa lines outlined in objective 1. Objective 3: Identify genes and expression patterns associated with salt tolerance. Approaches: Phenotypic selection for salt survival has been selected for genetic variation that provides salt tolerance. We hypothesize that selection for salt tolerance in alfalfa resulted in identificable changes in the alfalfa transcriptome. Oligonucleotide expresison arrays will be used to identify gene expression changes in the selected germplasm. Identification of these differentially expressed genes will lead to the elucidation of the molecular basis for tolerance mechanisms and the identification of expression polymorphisms that may be used as selection markers in future breeding efforts. Selected genes such as regulatory genes and ion transporters will be overexpressed in Arabidopsis and alfalfa. An enhanced salt tolerance in these overexpression plants will lead to identification of potential key genes that contribute to salt tolerance in these alfalfa germplasm.