Seed germination of three endangered subspecies of Discocactus Pfeiff. (Cactaceae) in response to environmental factors

Abstract

Temperature, light, water availability and excessive salt in the soil are among the abiotic factors that most influence the germination process in semiarid ecosystems. The aim of the present study was to determine the effect of these abiotic factors on seed germination in three subspecies of cactus: Discocactus bahiensis, D. zehntneri subsp. petr-halfarii and D. zehntneri subsp. zehntneri. Seeds were set for germination under two light conditions (12-h light/dark photoperiod and continuous darkness) and 10 temperature treatments [eight constant temperatures (10, 15, 20, 25, 30, 35, 40 and 45 °C) and two alternating temperatures (30 to 20 °C and 35 to 25 °C)]. Polyethylene Glycol (PEG) 6000 and sodium chloride (NaCl) were used to simulate water and saline stress, respectively, with the following osmotic potentials: 0.0, -0.2, -0.4, -0.6, -0.8 and -1.0 MPa. Three subspecies were positive photoblastic. The optimum temperature for germination was 25 to 35 ºC for D. bahiensis and D. zehntneri subsp. zehntneri, and 30 to 35 ºC for D. zehntneri subsp. petr-halfarii. The seeds of all three subspecies exhibited tolerance to water and saline stress, as germination was observed at potentials for up to -0.6 MPa in the PEG and NaCl solutions.

Seed traits and germination in the Cactaceae family: A review across Americas

“…In cacti, only four studies have assessed the germination at water potentials lower than -1.0 MPa (Martins et al 2012, Guerrero et al 2016, Aragón & Lasso 2018, Zerpa-Catanho et al 2019, maybe because in most cases the species do not achieve germination at such potentials (Flores & Briones 2001, Ramírez-Padilla & Valverde 2005, De La Rosa-Manzano & Briones 2010, Guillén et al 2011, Rodríguez-Morales et al 2013, Bispo et al 2018. The studies in cacti reveal that germination mainly occurs at water potentials between 0 and -0.6 MPa ( Figure 5) and at temperatures of 25 to 30 °C (Vega-Villasante et al 1996, Kin et al 2015, Bispo et al 2018. In some species, it has been observed that the water potentials of -0.2 MPa (Guillén et al 2009 or even -0.4 MPa (Flores & Briones 2001, Guillén et al 2011 or -0.6 MPa (Flores & Briones 2001) favor germination.…”

“…In some species, it has been observed that the water potentials of -0.2 MPa (Guillén et al 2009 or even -0.4 MPa (Flores & Briones 2001, Guillén et al 2011 or -0.6 MPa (Flores & Briones 2001) favor germination. Nevertheless, generally water potentials lower than -0.6 MPa notably decrease the percentage of germination (Meiado et al 2010, Guillén et al 2011, Bispo et al 2018. Thus, cactus seeds adapted to germinate at high soil moisture, but not necessarily at the soil field water capacity, would have an advantage germinating in arid environments.…”

“…These conditions could favor germination but could also result in death of seedlings through subsequent drought (Venable & Lawlor 1980). Approximately a dozen studies (Table 1) have evaluated the germination response of cacti faced with conditions of salinity (Romero-Schmidt et al 1992, Meiado et al 2010, Martins et al 2012, Ortiz et al 2014, Podda et al 2017, Bispo et al 2018. A germination response in the range of 0 to -0.6 MPa with NaCl is similar to the results obtained with PEG, even though there are species where the germination percentages with NaCl are higher than in a similar osmotic potential of PEG (Meiado et al 2010, Bispo et al 2018.…”

In vitro conservation and genetic diversity of threatened species of Melocactus (Cactaceae)

“…Finally, the polymorphism observed in this study indicates that the collections of M. paucispinus and M. glaucescens can be considered representative of the variability of the natural populations of these species. In vitro germination can be considered a viable strategy to ex situ conservation programs, as recommended by Nascimento et al (2018) when seedlings could be produced in a laboratory setting, thereby contributing to the conservation of the species in the eld and eliminating the threat of extinction.…”

Hydropriming changes temperature thresholds for seed germination of tree species from the Caatinga, a Brazilian tropical dry forest

“…The optimum temperature range can be related to the species' site of occurrence, dispersion period, and plant germination strategies (Meiado et al, 2016). In the Caatinga, a Tropical Dry Forest occurring mainly in the Northeast region of Brazil, many species have optimum germination ranging from 30 to 35 °C, evidencing that these plants have higher tolerance to high temperatures compared to species from more humid ecosystems (Meiado et al, 2012;Nascimento et al, 2018;Dantas et al, 2020).…”