Germination of Cactus Seeds Under Saline Stress

Abstract

Cactus seeds in seasonal dry tropical forests are subject to several stressors, such as salt stress which limits imbibition and therefore germination. Thus, this study aimed to compare germination performance of Cereus jamacaru subsp. jamacaru and Pilosocereus pachycladus subsp. pernambucoensis seeds under salinity conditions. To this end, NaCl and KCl solutions were used in the following osmotic potentials: 0.0 (control),-0.2,-0.4,-0.6,-0.8,-1.0, and-1.2 MPa. Seeds were placed to germinate at 25 °C and 12-hour photoperiod. The number of germinated seeds was counted daily for 21 days after root protrusion. The variables analyzed were: water content, germination, normal seedlings, germination speed index, and average germination time. The experimental design was completely randomized, following a 2 × 7 factorial scheme (species × osmotic potential) for each saline source. Water restriction and ionic effect caused by salts favored seed germination and vigor in both species at-0.2 and-0.4 MPa. However, from-0.8 MPa onwards, germination decreased significantly for both salts. Seeds of C. jamacaru subsp. jamacaru and P. pachycladus subsp. pernambucoensis were tolerant to salt stress since they germinated up to-0.8 MPa (NaCl) and-1.2 MPa (KCl). The latter occurred only for P. pachycladus subsp. pernambucoensis.

Germination responses of the invasive hedge cactus (Cereus uruguayanus) to environmental factors

“…When seeds from the −1.6 MPa treatment were washed and again incubated with water, germination was similar (90% to 99%) to that of the control, suggesting that water stress did not affect viability or germinability of the seeds, as was found for salt stress in Experiment 2. Seeds of C. jamacaru demonstrated a similar level of tolerance to water stress in the study by Silva and de Azerêdo (2022), with germination remaining unaffected at an osmotic potential of −0.6 MPa. However, substantial reductions occurred between −0.6 MPa and −0.8 MPa.…”

“…Conversely, Meiado et al (2010) reported that C. jamacaru exhibited a much higher degree of sensitivity to water stress, with reductions in germination beginning at −0.2 MPa and minimal germination observed at −0.6 MPa and −0.8 MPa. It is worth noting that Silva and de Azerêdo (2022) calculated osmotic potentials from NaCl concentrations using the Van’t Hoff equation (Salisbury and Ross 1991), whereas Meiado et al (2010) established solutions with different osmotic potentials by varying PEG concentrations, mirroring our approach in this research. This suggests that the latter method might be more appropriate for evaluating the germination response to water stress.…”

“…Reductions in germination of C. jamacaru were not detected until NaCl concentrations reached 160 mM (Meiado et al 2010; Silva and de Azerêdo 2022), with germination observed even at 200 mM (Meiado et al 2010). This raises the possibility that C. uruguayanus is even more tolerant to salt stress than could be detected under the present experimental conditions.…”

“…The latter species is native to northeastern Brazil and has been recorded as being invasive in Kenya (Witt and Luke 2017) and being a transformer, namely a weed that has changed the character, condition, form, or nature of an ecosystem over substantial areas relative to its extent (Richardson et al 2000), in South Africa (Henderson 2001). Investigations have been conducted into the effects of a number of factors on C. jamacaru germination, including light (Abud et al 2013; Alencar et al 2012), temperature (Abud et al 2013; Alencar et al 2012), water stress (Meiado et al 2010; Ortiz et al 2019; Silva and de Azerêdo 2022), salt stress (Meiado et al 2010; Silva and de Azerêdo 2022), and pH (Ortiz et al 2019). Results from these studies indicate that the optimum temperature for germination in C. jamacaru is between 25 and 30 C and that germination is susceptible to both water and salt stress.…”

Germination Performance of Physalis peruviana L. Seeds under Thermal and Water Stress Conditions

“…Silva and Azerêdo [64] also observed greater seed germination of two cactus species (Cereus jamacaru and Pilosocereus pachycladus) at a water potential of −0.2 MPa. Germination decreased from −0.2 MPa to −0.8 MPa, reaching zero at −1.0 and −1.2 MPa.…”