Seed dormancy of Cardiospermum halicacabum (Sapindaceae) from three precipitation zones in Sri Lanka

Abstract

This study investigated seed germination of Cardiospermum halicacabum, a medicinally important invasive species. • We compared mass, moisture content (MC), dormancy and dormancy-breaking treatments and imbibition and germination of scarified and non-scarified seeds of C. halicacabum from a low-elevation dry zone (DZ), low-elevation wet zone (WZ1) and mid-elevation wet zone (WZ2) in Sri Lanka to test the hypothesis that the percentage of seeds with water-impermeable seed coats (physical dormancy, PY) decreases with increased precipitation. • Seed mass was higher in WZ2 than in DZ and WZ1, while seed MC did not vary among the zones. All scarified DZ, WZ1 and WZ2 and non-scarified DZ and WZ1 seeds imbibed water, but only a few non-scarified WZ2 seeds did so. When DZ and WZ1 seeds were desiccated, MC and percentage imbibition decreased, showing that these seeds have the ability to develop PY. GA 3 promoted germination of embryos excised from fresh DZ and WZ1 seeds and of scarified WZ2 seeds. • At maturity, seeds from DZ and WZ1 had only physiological dormancy (PD), while those from WZ2 had combinational dormancy (PY+PD). Thus, our hypothesis was not supported. Since a high percentage of excised embryos developed into normal seedlings; this is a low-cost method to produce C. halicacabum plants for medicinal and ornamental purposes.

Elevation and phylogeny shape herbaceous seed dormancy in a biodiversity hotspot of southwest China

“…As an adaptive trait, deep seed dormancy appears to promote plant survival in high‐elevation habitats (Baskin & Baskin, 2014 ). Consistently, S. longifolia populations contain higher proportions of dormant seeds at high elevations (Cotado et al, 2020 ), Physalis species show an increase in dormant seeds with increasing elevation (Farooq et al, 2021 ), and C. halicacabum seeds show more complex seed dormancy at high elevations than at low elevations (Thusithana et al, 2021 ). These results suggest that natural selection pressure should favor plants that produce more dormant mature seeds at higher elevations.…”

“…Plants distributed over a wide range of elevations exhibit highly variable SDS due to different natural selection pressures (Allen & Meyer, 1998 ; Jurado & Flores, 2005 ; Veselá et al, 2020 ). For example, populations of Saxifraga longifolia (Saxifragaceae) from high elevations show the highest proportion of dormant seeds (Cotado et al, 2020 ), while Cardiospermum halicacabum (Sapindaceae) seeds collected from high‐elevation habitats show more complex SDS than seeds from low‐elevation habitats, requiring more periods of cold stratification to break dormancy (Orrù et al, 2012 ; Thusithana et al, 2021 ). Low‐elevation populations of wild grapevine ( Vitis vinifera subsp.…”

“…For example, the proportion of dormant seeds in Beta vulgaris (Amaranthaceae) populations varies from 0 to 1 under different ambient temperatures (Wagmann et al, 2012 ). Precipitation is another crucial limiting factor, with seeds developing in dry habitats more prone to dormancy due to adaptive predictive germination (Thusithana et al, 2021 ). Although changes in climate due to increasing elevation may drive elevational patterns of SDS variation, direct evidence is still lacking.…”

Seed (true seed plus endocarp) dormancy in Anacardiaceae in relation to infrafamilial taxonomy and endocarp anatomy

“…With regard to determining if a seed or other diaspore is water-permeable or impermeable, it is important to keep in mind that impermeability (i.e. PY) develops either during maturation drying on the mother plant or even during post-dispersal drying (Baskin and Baskin, 2014; Jaganathan, 2016, 2022; Thusithana et al, 2021). Seeds or fruits with PY become impermeable to water only when the moisture content (MC) of the diaspore falls below a species-specific MC threshold (see Table 6.2 in Baskin and Baskin, 2014); otherwise, the diaspore will remain water-permeable.…”

“…Gallará et al (2021) showed that the drupes of Lithraea molleoides (Anacardiaceae) needed post-dispersal drying for the induction of PY. However, in fact, the diaspore MC at which PY is induced also can vary even between populations of the same taxon growing under different environmental conditions (Thusithana et al, 2021). And furthermore, the development of PY does not occur at the same time for all seeds in the same days-after-pollination cohort and thus not at the same MC [see discussion in Qu et al (2010) and references cited therein].…”