Evolutionary genomics of climatic adaptation and resilience to climate change in alfalfa

Given the escalating impact of climate change on agriculture and food security, gaining insights into the evolutionary dynamics of climatic adaptation and uncovering climate-adapted variation empower the breeding of climate-resilience crops to face future climate change. Alfalfa (Medicago sativa subsp. sativa), the queen of forages with remarkable adaptability across diverse global environments, is an excellent model for investigating species' responses to climate change. We conducted population genomic analyses to unravel alfalfa's climatic adaptation and genetic susceptibility to future climate change, utilizing genome resequencing data from 702 accessions of 24 Medicago species. We found that interspecific genetic exchange has fueled the gene pool of alfalfa, particularly enriching defense and stress response genes. Inter-subspecific introgression between Medicago sativa subsp. falcata (subsp. falcata) and alfalfa not only aids alfalfa's climatic adaptation but also introduces genetic burden. A total of 1671 genes were associated with climatic adaptation, and 5.7% of them were introgression from subsp. falcata. Integrating climate-associated variants and climate data, we identified vulnerable populations to future climate change, particularly in higher latitudes of the northern hemisphere, serving as a clarion call for targeted conservation initiatives and breeding efforts. Moreover, we unveil pre-adaptive populations demonstrating heightened resilience to climate fluctuations, illuminating a pathway for future breeding strategies. This study enhances our understanding of alfalfa's local adaptation and facilitates breeding of climate-resilient cultivars, contributing to effective agricultural strategies facing future climate change.