article · Weed Science
This study investigates dormancy and germination mechanisms in the fruits of two invasive weed species, hoary cress and hairy whitetop. When seeds were removed from their enclosing fruit coats, both species showed no dormancy and achieved complete germination. However, intact fruits behaved differently. While hairy whitetop fruits germinated freely, intact hoary cress fruits displayed dormancy imposed by the fruit coat. Testing showed that the hoary cress fruit coat remains permeable to water and does not rely on mechanical constraints to restrict germination. Instead, the dormancy is chemical and physiological. Washing the fruits, dry storage during afterripening, and gibberellin applications all stimulated germination. Biochemical analyses demonstrated that abscisic acid in the fruit coat acts as the primary chemical inhibitor. As abscisic acid levels declined through washing or dry storage, hoary cress germination improved accordingly.
Invasive weeds present significant challenges to agriculture and land management. Understanding the physiological and chemical mechanisms controlling how and when these plants germinate provides valuable biological insights. Distinguishing between the different germination strategies of closely related invasive species helps researchers better understand how these plants adapt and persist in varied environments.
The findings represent early-stage physiological research that could inform the timing and design of weed management strategies for invasive species. While the abstract discusses potential roles for weed management, it does not detail specific commercial tools, products, or direct commercialisation pathways. Practical applications remain at a fundamental stage.
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Abstract This study provides a comparative analysis of the dormancy and germination mechanisms of the indehiscent fruits of hoary cress ( Lepidium draba L.) and hairy whitetop ( Lepidium appelianum Al-Shehbaz), two invasive weeds of the Brassicaceae. Germination assays comparing isolated seeds (manually removed from the fruits) and intact indehiscent fruits showed that the isolated seeds are nondormant and provided full germination for both species. In contrast to this, the species differed in the germination properties of their indehiscent fruits, in that L. appelianum fruits were nondormant, while the L. draba fruit coat (pericarp) conferred a coat-imposed dormancy. The pericarp of L. draba fresh fruit was water permeable, and neither mechanical scarification nor surface sterilization affected germination, supporting the concept that pericarp-mediated dormancy was not due to water impermeability or mechanical constraint. Washing of L. draba fruits with water, afterripening (dry storage), and treatment with gibberellin (GA) stimulated the germination of this species, all of which are indicative of physiological dormancy. Analyses of endogenous abscisic acid (ABA) and GA levels combined with treatment experiments with wash water from fresh and afterripened L. draba pericarps and with ABA dose–response quantification of germination revealed that ABA is a key component of a pericarp-mediated chemical dormancy in this species. Consistent with this, pericarp ABA levels decreased during afterripening and upon fruit washing, and isolated fresh or afterripened seeds did not differ in their ABA sensitivities. The possible roles of the ABA-mediated pericarp dormancy for the germination ecophysiology and weed management of these species are discussed.
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DOI: 10.1017/wsc.2019.33
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