Detecting Local Adaptation of Medicago truncatula to a Heterogeneous Saline Environment

As the world becomes warmer, agriculture is increasingly impacted by rising soil salinity and we must understand the mechanisms that influence plant adaptation to salt stress to enable effective crop breeding.  Salt tolerance is a complex plant phenotype and we know little about the pathways utilized by naturally tolerant plants. Here we use the model legume Medicago truncatula to understand natural variation of adaptation to saline environments. We collected 250 natural Tunisian accessions adapted to salinity, and from these accessions, we sequenced 96 individuals that performed the best and worst in saline conditions. Saline environments are extremely patchy and we find plants growing in both saline and non-saline soils.  Our results suggest that soil origin is a potential predictor of reproductive success in saline conditions. In agreement with previous studies, the data shows that flowering early could be an adaptive mechanism that may allow escape from salt stress. To identify candidate pathways involved in salinity adaptation, we have identified alleles with significant frequency differences associated with extreme phenotypic responses under saline conditions.