Abstract
AbstractThis study provides a comparative analysis of the dormancy and germination mechanisms of the indehiscent fruits of hoary cress (Lepidium drabaL.) and hairy whitetop (Lepidium appelianumAl-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 thatL. appelianumfruits were nondormant, while theL. drabafruit coat (pericarp) conferred a coat-imposed dormancy. The pericarp ofL. drabafresh 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 ofL. drabafruits 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 afterripenedL. drabapericarps 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.
Highlights
The noxious and invasive weeds hoary cress [Lepidium draba L.; known as Cardaria draba (L.) Desv. or heart-podded hoary cress] and hairy whitetop (Lepidium appelianum Al-Shehbaz; known as globe-podded hoary cress) belong to the Brassicaceae (Francis and Warwick 2008)
For the indehiscent fruits of L. draba, the tight encasement of the seeds by the pericarp did not allow the seeds to germinate within the fruits
To precisely quantify the seed sensitivities, we conducted dose–response experiments for the abscisic acid (ABA) treatment with fresh (Figure 6B) and afterripened (Figure 6D) L. draba seeds. These results demonstrated that increasing ABA concentrations caused a similar delay in the onset of the completion of seed germination of fresh and afterripened L. draba seeds (Figure 6)
Summary
The noxious and invasive weeds hoary cress [Lepidium draba L.; known as Cardaria draba (L.) Desv. or heart-podded hoary cress] and hairy whitetop (Lepidium appelianum Al-Shehbaz; known as globe-podded hoary cress) belong to the Brassicaceae (Francis and Warwick 2008). Heart-podded hoary cress] and hairy whitetop (Lepidium appelianum Al-Shehbaz; known as globe-podded hoary cress) belong to the Brassicaceae (Francis and Warwick 2008) These closely related species rank 8th out of the 45 most frequently listed noxious weeds of agricultural land, pastures, and riparian and waste areas in the western United States and Canada (Supplementary Figure S1; Mulligan 2002; Mulligan and Findlay 1974; Skinner et al 2000). Both L. draba and L. appelianum are native to Eurasia and have high competitiveness and invasiveness in their native, expanded, and introduced ranges (Francis and Warwick 2008; Hinz et al 2012).
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