We evaluated the responses to water deficit of twelve lines of Medicago laciniataand Medicago truncatula including eight lines from four Tunisian sympatric populations of both species, and four references lines of M. truncatula. They were exposed to two water treatments, well irrigated and drought-stress (33% of field capacity) for a period of 45 days. At harvest, we measured five quantitative traits including the length of stems (LS), aerial dry weight (ADW), root dry weight (RDW), RDW/ADW ratio and leaf area (LA). Analysis of variance showed that the variation of measured traits among studied lines was significantly explained by the effects of species, line, treatment, and their interactions. Treatment and species had the largest effects. We also analyzed the broad-sense heritability of the drought response index (DRI), defined as the ratio between the observed values with and without water deficit treatment. DRI of most measured traits had high broad-sense heritability (H²). The length of stems (LS) was the trait most affected by drought stress, while RDW/ADW ratio was not affected by drought. Generally, few significant differences were observed between DRI values of measured traits between lines within species as well as between lines of M. laciniata and M. truncatula collected from sympatric populations. Most of the correlations established between DRI values were positive. The environmental factors that most influenced variation of DRI values among populations were available phosphorus (P) and mean annual rainfall.
Key words: Medicago laciniata, Medicago truncatula, sympatric populations, lines, drought response index, environmental factors.
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