Investigating the link between seed morphology and germination success: insights from European common wild oat ( <i>Avena fatua</i> ) populations

Germination cardinal temperatures, germination rate for 50% of seeds (GR₅₀), and seed traits are interrelated and allow prediction of germination behaviour based on seed characteristics. We examined the relationships between seed traits and germination cardinal temperatures in 122 Avena fatua populations from 16 European countries, analysing data from 22,000 seeds using image analysis. By germination testing across a temperature range of 5-35°C, the germination rate for 50% of seeds (GR₅₀), base temperature (T_b), optimal temperature (T_o), and ceiling temperature (T_c) were estimated using a Dent-like segmented model. A primary response screening analysis revealed that seed colour was the main determinant of GR₅₀. For T_b, seed colour and surface hairiness were influential factors, while T_o and T_c were affected by seed colour and the awn attachment point on the lemma. Predictions from artificial neural networks indicated that smaller seeds with shorter awns, wider awn angles relative to the seed axis, higher attachment points on the lemma, and lower surface hairiness are likely to have higher germination rates. Darker-coloured seeds had higher T_b values than lighter-coloured seeds. Seeds with awns attached higher on the lemma predominantly had higher T_b values. Black seeds, the most common colour, had a lower T_c than other colours. Considering geographic locations linked to germination cardinal temperatures, seeds from higher latitudes had lower T_b values, and seeds from lower longitudes were predicted to have lower T_c. This study demonstrated that specific seed morphological traits, such as seed mass, awn length and angle, hairiness, and awn attachment, consistently influence germination performance under varying environmental conditions. These associations suggest adaptive differentiation shaped by both climate pressures and geographic gradients.