Aluminum tolerance in Medicago truncatula germplasm

Aluminum (At) toxicity is a major limiting factor of crop production in acidic soils. Medicago truncatula Gaertn., a close relative of alfalfa (M. sativa L.), is negatively affected by Al toxicity. The objective of this study was to assess the variation for Al tolerance among M. truncatula accessions held in the USDA National Plant Germplasm System, with the long-term goal of identifying Al tolerance genes to be used for alfalfa improvement. Three hundred twenty-one accessions of M. truncatula, from 20 different countries, were screened for Al tolerance in a hydroponics approach. Seed from each M. truncatula accession were surface sterilized and germinated before being grown in hydroponics. Ten germinated seedlings were transferred to a hydroponics culture tank containing modified Blaydes medium without aluminum and ten were transferred to a second tank containing modified Blaydes medium with 50 mu M Al. Seedlings were grown for 5 d and root length was measured. Relative root growth in Al medium was used as a measure of All tolerance. Relative root growth varied from 0.35 to 1.09, indicating that sufficient variation exists within this collection of M. truncatula accessions to select sensitive and tolerant accessions, which could be used to identify QTL for Al tolerance, the first step in a map-based cloning approach to discover Al tolerance genes.