More than Just a Shell: Indehiscent Fruits Drive Drought-Tolerant Germination in Invasive Lepidium Species

This study aims to assess the drought stress tolerance of germinating seeds of the invasive indehiscent fruit-producing <i>Lepidium</i> species, specifically <i>Lepidium appelianum</i>, <i>Lepidium draba</i>, and the invasive dehiscent fruit-producing <i>L. campestre</i>. Drought stress tolerance experiments were conducted using various concentrations of polyethylene glycol (PEG) following standard protocols. The results revealed that seeds/fruits of <i>L. appelianum</i> and <i>L. draba</i> exhibited significantly higher drought stress tolerance compared to seeds of <i>L. campestre</i>. Fresh seeds and fruits of <i>L. appelianum</i> were capable of germinating under various drought stress treatments, while fresh and after-ripened seeds and fruits of <i>L. draba</i> germinated in every condition except for -0.8 MPa. Conversely, <i>L. campestre</i> fresh seeds did not germinate under the most severe drought stress conditions (-0.6 and -0.8 MPa). It is crucial to note that fresh fruits of <i>L. draba</i> displayed pericarp-mediated chemical dormancy, while fresh seeds of <i>L. campestre</i> demonstrated physiological dormancy. However, fresh seeds and fruits of <i>L. appelianum</i> did not exhibit any dormancy. This study suggests that germinating seeds and fruits of <i>L. appelianum</i> demonstrate the strongest tolerance to drought stress, while <i>L. draba</i> exhibits moderate tolerance. On the contrary, <i>L. campestre</i> seeds display the least tolerance to drought stress. The differences in drought stress tolerance among the studied <i>Lepidium</i> species reflect the climatic facets in their native distribution areas. Given the potential high invasiveness associated with the drought stress tolerance of <i>L. appelianum</i> and <i>L. draba</i>, it is imperative to develop special control strategies to manage these invasive species in the face of future climate change.