Light stress conditions affect variability in the phenotypic expression of germination in Mammillaria carnea from different origins and genetic families

The challenges arising from environmental stress conditions and the intrinsic limitations of their sessile nature strongly affect plants throughout their life cycle. Evolutionarily, plants have developed mitigation strategies, such as acclimation and phenotypic plasticity, to thrive in diverse environmental conditions. In semi-arid environments, light stress plays an important role in seed germination. The objective of this study was to experimentally assess the variability in the phenotypic expression of germination among genetic families of the cactus Mammillaria carnea obtained from different micro-environments along a light stress gradient. Specifically, we investigated germination under white light and far-red-rich light conditions, aiming to simulate lighting conditions with and without canopy cover. The highest germination percentages were observed under white light conditions. However, within the micro-environments associated with Neltuma laevigata and Parkinsonia praecox, greater phenotypic variability and genetic independence were evident under far-red-rich light compared to direct solar radiation. This suggests that while high light intensity enhances seed germination, it also reduces phenotypic expression variability, potentially resulting in decreased evolutionary adaptability in M. carnea populations in high-light stress environments.