Data_Sheet_1_The History of Domestication and Selection of Lucerne: A New Perspective From the Genetic Diversity for Seed Germination in Response to Temperature and Scarification.zip

Lucerne (Medicago sativa), a major perennial pasture legume, belongs to a species complex that includes several subspecies with wild and cultivated populations. Stand establishment may be compromised by poor germination. Seed scarification, deterioration and temperature have an impact on germination. The objective of this study was to analyse the genetic diversity of lucerne germination in response to three factors: (1) temperature, with seven constant temperatures ranging from 5 to 40°C, was tested on 38 accessions, (2) seed scarification was tested on the same accessions at 5 and 22°C, (3) seed deterioration was tested on two accessions and two seed lots at the seven temperatures. The germination dynamics of seed lots over time was modelled and three parameters were analysed: germinability (germination capacity), maximum germination rate (maximum% of seeds germinating per time unit), and lag time before the first seed germinates. Seed scarification enhanced germinability at both temperatures and its effect was much higher on falcata and wild sativa accessions. Incomplete loss of the hardseededness trait during domestication and selection is hypothesised, indicating that the introduction of wild material in breeding programmes should be followed by the selection for germinability without scarification. Seed lots with altered germinability had low germination at extreme temperatures, both cold and hot, suggesting that mild temperatures are required to promote germination of damaged seed lots. A large genetic diversity was revealed for germination (both capacity and rate) in response to temperature. All accessions had an optimal germination at 15 or 22°C and a poor germination at 40°C. The sativa varieties and landraces had a high germination from 5 to 34°C while the germination of falcata and the wild sativa accessions were weakened at 5 or 34°C, respectively. These differences are interpreted in terms of adaptation to the climate of their geographical origin regions in order to escape frost or heat/drought risks. These new findings give insights on adaptation and domestication of lucerne in its wide geographic area. They suggest further improvement of germination is needed, especially when introducing wild material in breeding pools to remove scarification requirements and to limit differences in response to temperature.

紫花苜蓿（Medicago sativa）是一类重要的多年生牧草豆科植物，隶属于包含多个亚种的物种复合体，该复合体涵盖野生与栽培种群。发芽不良可能制约苜蓿建植，而种子划破处理、种子劣变及温度均会对发芽过程产生影响。本研究旨在分析紫花苜蓿发芽对三种因素的遗传多样性：(1) 温度效应：在38份种质上测试了5℃至40℃范围内的7个恒温梯度；(2) 种子划破处理效应：在5℃与22℃条件下对同批种质开展测试；(3) 种子劣变效应：在7个温度梯度下对2份种质与2个种子批进行测试。研究对种子批随时间变化的发芽动态进行了建模，并分析了三项参数：发芽能力（germinability，即发芽容量）、最大发芽速率（单位时间内的最大发芽种子占比）以及首粒种子萌发前的滞后期。种子划破处理在两个测试温度下均提升了发芽能力，且其效应在镰荚苜蓿（falcata）与野生紫花苜蓿种质上更为显著。研究推测，在驯化与选育过程中，种子硬实特性并未完全丧失，这提示将野生材料引入育种项目后，需筛选无需划破处理即可正常发芽的种质。发芽能力受损的种子批在极端温度（低温与高温）下均表现出较低的发芽率，这表明需采用温和温度以促进受损种子批的萌发。本研究揭示了紫花苜蓿发芽（包括发芽能力与速率）对温度响应的丰富遗传多样性。所有供试种质均在15℃或22℃下达到最佳发芽效果，而在40℃时发芽表现不佳。栽培紫花苜蓿品种与地方品种在5℃至34℃范围内均维持较高发芽率，而镰荚苜蓿与野生紫花苜蓿种质分别在5℃与34℃时发芽能力出现减弱。上述差异被认为是对其地理起源区域气候的适应策略，以规避霜冻或热/干旱风险。本研究的新发现为紫花苜蓿在广阔地理范围内的适应与驯化机制提供了新的研究视角，并提示需进一步优化发芽性能，尤其是在将野生材料引入育种群体时，需去除种子划破处理的需求并降低其对温度响应的差异。