Misunderstanding on germination sensu stricto leads us to a false positive germination‐dormancy balance in diaspores of Paepalanthus chiquitensis Herzog (Eriocaulaceae), a threatened everlasting flowering species

Abstract

Although germination sensu stricto and germination–dormancy balance are essential to each other, few reports demonstrate the effects of their relationship on patterns of seed–seedling transition. We studied this relationship by using diaspores of Paepalanthus chiquitensis, a threatened everlasting flowering species. We assessed three aspects: (a) water dynamics in germinating diaspores, (b) thermal stimulation (35, 40, 50, 60 and 70°C for 30 min) and (c) imbibition (4 hr) in growth stimulators (100, 200 or 300 mg · L−1 GA3; 0.1% KNO3). Our findings demonstrate that there are no barriers in the diaspore for diffusion. Additionally, there is high variability in diaspore permeability, and the germination of the species has two steps divided into five stages. These stages were defined by inflections on velocity in water dynamics, which ranged from −0.05 to 0.05 g · hr−1, where only the last stage (Phase V) is associated with the second step of germination sensu stricto. The imbibition phase was the shortest germination phase (1.3 hr), whereas the predominantly biochemical phase was the longest (5 days after sowing [DAS]). Germinability was high (77.5–86.5%), with high daily embryo protrusion (2.46–3.03 diaspores · day−1). Protocorm emergence marked the end of the first step of germination sensu stricto (9 DAS), and first protocorm rupture (11 DAS) marked the end of the second step. The growth stimulus only concentrated the germination process, showing that the diaspores do not have primary dormancy. Knowing these diaspores’ peculiarities during germination sensu stricto avoids a false positive statement on the existence of diaspore dormancy.

The great diversity in kinds of seed dormancy: a revision of the Nikolaeva–Baskin classification system for primary seed dormancy

“…A similar embryo and germination morphology as described for Trithuria occurs in the autotrophic monocot families Eriocaulaceae, Mayacaceae and Xyridaceae (Baskin and Baskin, 2018). Fresh seeds of various tropical species of Eriocaulaceae and Xyridaceae from the cerrado of Brazil have been reported to be nondormant, that is, no primary dormancy (Garcia et al, 2020;Gonçalves-Magalhães et al, 2020;Oliveira et al, 2021;Zupo et al, 2021). However, seeds of Eriocaulon septangulare from temperate eastern North America were dormant and required cold stratification (1-3°C submerged in water) for germination; they did not come out of dormancy when stored wet (in water) or dry at laboratory temperatures or when stored dry at 1-3°C (Muenscher, 1936).…”

Cross-pollination is more important than gibberellin application in the germination of the everlasting flowers ofJaneirona carrasqueira(morphotype ofComanthera bisulcata)

“…Species germination was distributed over time for both treatments. Polymodal germination behavior can be attributed to the fact that seeds of native species often exhibit high genetic variability, which represents a crucial adaptive strategy for their survival (Gonçalves-Magalhães et al, 2021). Thus, the seeds that did not germinate at the end of the period with favorable conditions reduce their metabolism, activating it in adequate environmental conditions for their establishment (Gonçalves-Magalhães et al, 2021).…”

“…Polymodal germination behavior can be attributed to the fact that seeds of native species often exhibit high genetic variability, which represents a crucial adaptive strategy for their survival (Gonçalves-Magalhães et al, 2021). Thus, the seeds that did not germinate at the end of the period with favorable conditions reduce their metabolism, activating it in adequate environmental conditions for their establishment (Gonçalves-Magalhães et al, 2021). This indicates that this species can establish seed banks in the soil, which occur in most species from Campo Rupestre (Garcia et al, 2014;Garcia et al, 2020).…”

“…Owing to their significant economic and social impact (Gonçalves-Magalhães et al, 2021), combined with the endemic distribution of many species with everlasting flowers, measures to ensure their preservation are necessary. These measures include studying the reproductive conditions (pollination, crossing, and germination systems) of commercialized species to improve ex situ cultivation techniques, and design adequate management strategies for native populations subjected to extractivism (Schmidt et al, 2008;Horiuchi et al, 2020).…”