SHOOT BIOMASS PRODUCTION AMONG ACCESSIONS OF MEDICAGO TRUNCATULA EXPOSED TO NACL

Authors: VEATCH, MAREN - UNIV OF ARIZONA; SMITH, STEVEN - UNIV OF ARIZONA; Vandemark, George

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2003
Publication Date: 4/1/2004
Citation: Veatch, M.E., Smith, S.E., Vandemark, G.J. 2004. Shoot biomass production among accessions of medicago truncatula exposed to nacl. Crop Science. 44:1008-1013.

Interpretive Summary: Crop production is affected by salinity on approximately one third of the world's irrigated agricultural land, and the amount of land affected by salinity is increasing. A major focus of plant breeding efforts in many areas has been to maintain or improve crop productivity in salt-affected environments, typically by selecting for increased salt tolerance. Alfalfa (Medicago sativa) is the fourth most important crop in American agriculture in terms of both total acreage and production value. Alfalfa is quite sensitive to salinity encountered either in irrigation water or in soil. A necessary step for improving tolerance in alfalfa to salinity is to determine the genetic factors responsible for improved plant performance in the presence of salinity. Unfortunately, alfalfa has several characteristics that make genetic analysis rather difficult. First, alfalfa has four copies of each chromosome, unlike most plants and all animals, which only have two copies. Four copies of each chromosome results in very complex arrangement of genes. Additionally, alfalfa cannot be self-pollinated, so crosses have to be made between different plants to produce populations for genetic analysis. However, there is another plant species, the barrel medic (Medicago truncatula), a close relative of alfalfa, which has characteristics that make it a good plant for studying genetics. The barrel medic has only two copies of each chromosome and can be self-pollinated. We examined over 20 different populations of the barrel medic to try to identify populations that were particularly adapted to perform in the presence of salt stress. Plants were watered with fresh water or with water containing different amounts of salt. We found that the populations with the highest yields in the presence of salt stress were also the populations that had the highest yields in the absence of salt stress. These results suggest that we still have to examine more populations of the barrel medic to identify a population that is especially adapted to provide high forage yields in the presence of salt stress.

Technical Abstract: Increased salt tolerance would improve utilization of salt-sensitive crop plants such as alfalfa (Medicago sativa L.). In order for selection for salt tolerance to be more efficient, it is useful to know whether improved productivity under saline conditions is due to unique physiological responses to salinity or merely the carry over of increased yield that was selected for in a non-saline environment. Medicago truncatula Gaertn., a self-pollinated relative of alfalfa, was used to examine the response of specific genotypes across a range of salinities. This was done by evaluating the change in fresh shoot biomass production of greenhouse-grown mature plants and seedlings of different accessions of M. truncatula in response to four levels of salinity imposed as NaCl. Those accessions with the highest fresh shoot biomass production under non-saline irrigation also had the highest fresh shoot biomass production under all salinity levels. The high correlation between an accession's fresh shoot biomass under non-saline and saline irrigation indicate no unique physiological adaptation to salinity in the accessions of M. truncatula evaluated.