Germination characteristic of Silphium perfoliatum L. seeds

The mean value of germinated seeds with PP was about 1.7% higher than with TP (Table 2). Seeds in TP showed fungal infections. In contrast, the folds in the pleated paper (PP) served as a barrier, preventing fungi from growing from one seed to the next. PP seems better suited for the germination of S. perfoliatum L. seeds with their flat shape and large seed surface.

Table 2

Mean value and standard deviation of germinated seeds for selected factor levels

Tabelle 2. Mittelwert und Standardabweichung gekeimter Samen für ausgewählte Faktorstufen

Table 3

Resulting germination test method for Silphium perfoliatum L. to exploit the germination potential

Tabelle 3. Resultierende Keimfähigkeitstestmethode für Silphium perfoliatum L. zur Ausschöpfung des Keimfähigkeitspotentials

Table 4

Multiple Comparisons of the selected factors temperature, pretreatment and prechilling

Tabelle 4. Mehrfachvergleiche der ausgewählten Faktoren Temperatur, Vorbehandlung und Vorkühlung

GA₃ and KNO₃ solutions can affect the metabolic activity of seeds (Baskin and Baskin, 2004). Our experiments show that the treatment with GA₃ and KNO₃ solutions led to significantly higher germination than the untreated control with water (Table 2 and Figure 1). The greatest effect on germination capacity was achieved with GA₃. GA₃ has the opposite effect to abscisic acid (ABA) and the exact ratio of GA₃ to ABA determines, on a plant-hormone level, whether a seed will start to germinate or remain dormant. ABA accumulates in the embryo during seed ripening and is responsible for primary dormancy (Kucera et al., 2005). In contrast, GA₃ induces growth of the embryo and increases the availability of nutrients (Koornneef et al., 2002; Hilhorst, 1995). The ratio of GA₃ and ABA at S. perfoliatum L. seeds has probably been shifted by adding GA₃ solution and consequently the germination capacity increased. This effect suggests the presence of a physiological dormancy. The experiments of Vetter et al. (2010) and Trölenberg et al. (2012) with S. perfoliatum L. seeds using GA₃ solution also showed a germination capacity close to the theoretically possible maximum.

Figure 1

Light and its intensity can have a substantial effect on dormancy and germination (Oh et al., 2006). Light had a positive effect on the germination of S. perfoliatum L. during the preliminary experiments. To investigate this effect, 12- and 24-hour light variants were tested. The 12-hour light–dark cycle with a light intensity between 400 and 1200 lux resulted in significantly higher germination capacities than the 24-hour light variant (Table 2).

Favorable environmental conditions, like specific temperature ranges, are important for germination; otherwise the seeds cannot germinate (Baskin and Baskin, 2004) or fall into secondary dormancy (Hilhorst, 1998; Finch-Savage and Leubner-Metzger, 2006). If seeds have physiological dormancy, alternating temperatures can be used to break their dormancy (Long et al., 2014).

Temperature had the greatest effect on germination capacity over all the five factors in our experiment. The differences between the temperature variants were highly significant. As Table 2 and Figure 1 show, the temperature cycles of 20/30°C every 12 hours showed distinctly more germination than constant temperatures at 20°C or 30°C. In combination with the GA₃ solution, an average germination capacity of over 85% was achieved.

Trölenberg et al. (2012) extensively studied the effect of various constant and changing temperatures on the germination of S. perfoliatum L. seeds at a temperature-gradient germination table. The results showed that germination was positively influenced by higher temperatures up to 30°C and by alternating temperatures with higher amplitude.

Several decades ago, Sokolov and Gritsak (1972) and Troxler and Daccord (1982) recommended sowing S. perfoliatum L. seeds in late autumn, at the latest 15–20 days before the first night frost, using freshly gathered seeds or in spring with seeds that had been stratified for 2 months. Accordingly, the factor “prechilling” was included in the model, as prechilling is particularly suitable to break the physiological dormancy (Long et al., 2014).

The results confirmed that prechilling has a positive effect on the germination capacity. The germination capacity of the variants with prechilling (7 days / 10°C; 7 days / 5°C; 7 days / 0°C) was highly significantly higher than the untreated control (no prechilling). The differences between the individual prechilling temperatures were not pronounced, but still significant. Therefore, a prechilling phase at 0°C over 7 days is advisable to achieve a high germination capacity and to break the physiological dormancy.

The results are consistent with the conclusions of Vetter et al. (2010) and Trölenberg et al. (2012). They recommend a prechilling phase at 5°C over 5 and 7 days respectively. Franzaring et al. (2014) used a four-week prechilling period in climate chambers for their growth experiments with S. perfoliatum L. The temperatures varied between 3°C and 11°C, causing stratification and breaking of the seed dormancy.