Abstract
Zephyra compacta is a geophyte plant endemic to Chile with the potential to be used as an ornamental crop. Its natural habitat is the coastal plains of the Atacama Desert, with a climate described as coastal desert with abundant cloudiness. This work analyzes the germination of Z. compacta seeds at 10, 15, 20, and 25 °C. Seeds were collected in 2011 and stored for 2 years and 4 months at 5 °C, until sowing. A mathematical model was used for germination analysis, p = A{1 − exp[−k(t − t0)]}, where p is the germination percentage at a certain time t, A is the final germination percentage, t0 is the estimated time of germination of the first seed, and k is the measure of the spread of the time to germination. Furthermore, the rate of germination of the median seed to germinate (1/tA/2) was included. The germination curves showed a coefficient of determination (R2) between 0.86 and 0.99. The results show that temperature range for germination is from 10 to 20 °C, where A is over 90%. In this range, other evaluated parameters (t0, k, and 1/tA/2) show no significant difference, with the exception of k at 15 °C. At this temperature, germination is obtained in a shorter period of time and could be considered as the optimal temperature within the range. Finally, 25 °C is a supraoptimal temperature, where the value of A decreased to 30%.
The Zephyra genus, of the Tecophilaeaceae family, is endemic to Chile’s Atacama Desert (Muñoz and Moreira, 2000) and comprises four species: Z. compacta, Zephyra cyanocrocus, Zephyra elegans, and Zephyra violiflora (Buerki et al., 2013; Ravenna, 1988). The species Z. cyanocrocus and Z. violiflora characteristically have one or two flowers per inflorescence and three sterile stamens, as opposed to Z. compacta and Z. elegans, which have branched or paniculate inflorescences and two sterile stamens (Buerki et al., 2013; Simpson and Rudall, 1998). Zephyra compacta was the last species of the genus to be described and, according to Ehrhart (2001), it differs from Z. elegans because of its compact growth, wider and succulent leaves, more branched inflorescence, and that it has only pure white flowers, with smaller and curved back tepals (Figs. 1–2).
Zephyra compacta at flowering stage in its natural habitat (29°10′S–71°29′W, Caleta Apolillado, Atacama Desert, Chile).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
Zephyra compacta at flowering stage in its natural habitat (29°10′S–71°29′W, Caleta Apolillado, Atacama Desert, Chile).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
Zephyra compacta at flowering stage in its natural habitat (29°10′S–71°29′W, Caleta Apolillado, Atacama Desert, Chile).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
Zephyra compacta at fruiting stage in its natural habitat (29°17′S–71°18′W, Quebrada Los Choros, Atacama Desert, Chile).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
Zephyra compacta at fruiting stage in its natural habitat (29°17′S–71°18′W, Quebrada Los Choros, Atacama Desert, Chile).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
Zephyra compacta at fruiting stage in its natural habitat (29°17′S–71°18′W, Quebrada Los Choros, Atacama Desert, Chile).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
The Zephyra genus has a high ornamental value, where the best-known and studied species are Z. cyanocrocus and Z. elegans (Eyzaguirre and García de la Huerta, 2002; Kim and Ohkawa, 1999, 2001; Kim et al., 1996, 1998; Vidal et al., 2012; Yáñez et al., 2005). Zephyra compacta, as opposed to Z. elegans, has the potential to be used as a potted plant because of its compact growth. However, key aspects that contribute to the domestication and ornamental use of Z. compacta are unknown, such as the environmental conditions for its germination, especially the temperature.
Zephyra compacta’s natural habitat (29°17′S–71°18′W, Quebrada Los Choros, Atacama Desert) corresponds to the coastal plains formed by fluviomarine sediment with a costal desert climate with abundant cloudiness (Cereceda et al., 2008; Novoa and López, 2001). The monthly average temperatures vary between 13.0 and 20.5 °C with a diurnal temperature variation of 7.5 °C; the monthly high and low temperatures are 24.5 and 9.8 °C, that occur in January and July, respectively (Fig. 3). The average of clear days per year is only 44. The precipitations are in the form of rainfall and are scarce and extremely variable. They usually occur at the end of autumn and winter (May to August) and are uncommon in spring (Antonioletti et al., 1972; Juliá et al., 2008). The annual precipitation is between 25 to 50 mm, with seasonal variations in dry and humid years that range from zero to 100 mm. According to the records, average rainfall occurs in no more than 4 d a year (Antonioletti et al., 1972; DGA, 2004). Irregularly high rainfall (>15 mm) normally occurs during the phenomena of El Niño–Southern Oscillation, and as a consequence, the emergence of more than 200 species of annual plants and geophytes occur, including Z. compacta (Gutiérrez, 2008).
Climograph of coastal Atacama Desert, adapted from Novoa and Villaseca (1989). Precipitation (solid bars), monthly average temperature (solid line), monthly maximum temperature (segmented line), and monthly minimum temperature (dot line).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
Climograph of coastal Atacama Desert, adapted from Novoa and Villaseca (1989). Precipitation (solid bars), monthly average temperature (solid line), monthly maximum temperature (segmented line), and monthly minimum temperature (dot line).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
Climograph of coastal Atacama Desert, adapted from Novoa and Villaseca (1989). Precipitation (solid bars), monthly average temperature (solid line), monthly maximum temperature (segmented line), and monthly minimum temperature (dot line).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
In desert climates, the germination and emergence of seedlings is sporadic since this process is associated with water availability (Black et al., 2006). With few exceptions, rainfall occurs only in winter and therefore it can be expected that the seeds require temperatures typical of this season to germinate (Baskin and Baskin, 2014). Therefore, we hypothesize that the germination temperature of Z. compacta seeds should correspond to winter temperatures of 10 to 15 °C in its natural habitat, which is the season when the records show there is a higher probability of rainfall (Novoa and Villaseca, 1989). Considering the previous background, the objective of this study is to determine the temperature range and optimal temperature for germination of Z. compacta.
Materials and Methods
Zephyra compacta seeds were collected by Mr. Michail Belov of Chileflora (www.chileflora.com) in Nov. 2011 in Quebrada Los Choros (29°17′S–71°18′W), Atacama Desert, Chile, and, to preserve seed vigor, stored at 5 °C (Black et al., 2006) until germination trials were conducted (Apr. 2014).
The germination trials were conducted in growth chambers units at 10, 15, 20, and 25 ± 2 °C. For each of these treatments, four replicates were used, each consisting of 50 seeds in a petri dish with absorbent paper (9-cm diameter). Seeds were disinfected for 3 min in a solution of Captan® at 1% (Captan® 50WP; N-(trichloromethylthio)-4-cyclohexene-1,2-dicarboximide; Arysta LifeScience, Cary, NC), later rinsed three times and then sown. Three to four milliliters of water were added to each petri dish and then sealed with plastic paraffin tape. During germination time, additional water was added only if necessary. Germination was recorded every 2 d for a period of 4 weeks. A seed was considered to be germinated when the emergent radicle was at least 2 mm.
The germination data for each treatment was fitted to the model p = A{1 − exp[−k(t − t0)]} used by Mobayen (1980), where p is germination percentage at a determined time t, A is the final germination percentage, t0 is the estimated time of germination of the first seed, and k is a measure of the spread of the time to germination. Parameter k expresses time required from the first to the last seed to germinate, where values of near one and values near zero indicate short and long time, respectively. Furthermore, the rate of germination of the median seed to germinate (1/tA/2) was included, where tA/2 is the time required to reach median seed germination and is calculated as t0 + 0.693/k.
Statistical test used for comparisons was the confidence interval for the difference of two proportions at P ≤ 0.05 for the final germination percentage A. Differences for t0, k, and 1/tA/2 were tested by calculating the confident intervals related to the corresponding regression coefficients obtained from the model p = A{1 − exp[−k(t − t0)]} at P ≤ 0.05 (Walpole et al., 2012).
Results and Discussion
The germination curves produced by the data fitted to the model used by Mobayen (1980) had coefficients of determination (R2) ranging from 0.86 to 0.99 (Table 1; Fig. 4).
Temperature effect on germination of Zephyra compacta, where parameter A is the final germination percentage, t0 is the estimated time of germination of the first seed, k is a measure of the spread of the time to germination, and 1/tA/2 is the rate of germination of the medians seed to germinate. Seeds were stored at 5 °C for 2 years and 4 months until sowing.
Germination curves fitted to the model p = A{1 − exp[−k(t − t0)]} used by Mobayen (1980). Seeds of Zephyra compacta germinated at 10 °C (□), 15 °C (◊), 20 °C (∆), and 25 °C (○) after 2 years and 4 months in storage (5 °C).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
Germination curves fitted to the model p = A{1 − exp[−k(t − t0)]} used by Mobayen (1980). Seeds of Zephyra compacta germinated at 10 °C (□), 15 °C (◊), 20 °C (∆), and 25 °C (○) after 2 years and 4 months in storage (5 °C).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
Germination curves fitted to the model p = A{1 − exp[−k(t − t0)]} used by Mobayen (1980). Seeds of Zephyra compacta germinated at 10 °C (□), 15 °C (◊), 20 °C (∆), and 25 °C (○) after 2 years and 4 months in storage (5 °C).
Citation: HortScience horts 52, 3; 10.21273/HORTSCI11623-16
Final germination percentage (A) for germination temperature treatments of 10, 15, and 20 °C was over 90%, and showed no differences between them (Table 1). According to these data, temperature range for germination of Z. compacta is 10 to 20 °C. In this temperature range, with the exception of the value of the spread of the time to germination (k), the value of the rest of the parameters (t0 and 1/tA/2) also showed no significant differences. At 15 °C, the value of the spread of the time to germination (k) reaches its highest value (0.692/d) when compared with 10 and 20 °C, and therefore, 15 °C should be considered as the optimal temperature for germination of Z. compacta.
It is worth mentioning that the temperature range (10 to 20 °C) in which Z. compacta reaches 90% germination or higher, coincides with the monthly average temperature range present during the entire year in its natural habitat (Novoa and López, 2001). When monthly higher and lower temperatures are considered, favorable temperature conditions for germination occur from April to November. However, the greatest probability for precipitation only occurs from May to August (Juliá et al., 2008; Novoa and Villaseca, 1989). Therefore, it is reasonable to infer that in a coastal desert climate with abundant cloudiness, temperature should not be the limiting factor for germination of Z. compacta at any time of the year. Instead, we propose that that the limiting factor is the availability of water via rainfall, as occurs with other desert plants (Black et al., 2006; Gutiérrez et al., 2000; Vidiella and Armesto, 1989).
Zephyra compacta presents a temperature range for germination of 10 to 20 °C similar to species coexisting in the same habitat such as Pasithea coerulea and Schizanthus litoralis (Jara et al., 2006; Schiappacasse et al., 2005). Interestingly, other species from the same habitat have a more restrictive temperature range for germination (10 to 15 °C) such as Leucocoryne dimorphopetala (De la Cuadra et al., 2016). According to Schiappacasse et al. (2005), Z. violiflora also has a temperature range for germination similar to L. dimorphopetala; however, this species inhabits sites with Mediterranean climate (Buerki et al., 2013).
The final germination percentage (A) at 25 °C decreased significantly to 30%. In its natural habitat, high daily temperatures of 25 °C or more are typical in summer, during the months of December to March and normally coinciding with the absence of precipitations (Novoa and Villaseca, 1989). Similar behavior is observed in Z. elegans, species that coexist in the same habitat, which under in vitro conditions at 25 °C and darkness, maximum germination was only 40% (Vidal et al., 2012). Thus, 25 °C seems to be a supraoptimal temperature for Z. compacta.
For determination of optimal temperature, other parameters (t0, k, and 1/tA/2) could be useful. In this investigation, when final germination percentage (A) of Z. compacta reached its maximum, but was similar at different temperatures, the highest value of parameter k, which indicates the shortest time from first to last seed to germinate, was helpful as a second parameter to determine optimal temperature. Similar situation was observed in several species of Leucocoryne where the optimal temperatures were determined by the highest values of k (De la Cuadra et al., 2016).
In conclusion, Z. compacta seeds have a high germination in the temperature range of 10 to 20 °C, with 15 °C being optimal, congruent with the environmental conditions of its natural habitat.
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