Germination rates of four Chilean forest trees seeds: Quillaja saponaria, Prosopis chilensis, Vachellia caven, and Caesalpinia spinosa

Samples

All seeds were collected from adult trees. Q. saponaria seeds were collected in VIII Región, Chile; seeds from V. caven, C. spinosa and P. chilensis were from Región Metropolitana, Chile. The seeds were collected between February and April 2017. Information about collection was obtained from the seed provider, CESAF Antumapu, http://cesaf.forestaluchile.cl/.

Table 1 and Table 2 specify the initial number of seeds per plate and the percentage of germinated seeds in some days are shown. Figure 1 shows the obtained values of time taken for 50% of seeds to germinate (TG50).

Figure 1. Time taken for 50% of seeds to germinate (TG50) for each species.

Interpolation of Q. saponaria (A), P. chilensis (B) and V. caven TG50 (C), and extrapolation of C. spinosa TG50 (D).

Pretreatment

Pretreatment conditions were suggested by the provider. Briefly, seeds of Q. saponaria were hydrated in tap water overnight. Seeds of P. chilensis were scarified in 95–97%, analytical grade H₂SO₄ for 10 minutes and then hydrated in tap water overnight. Seeds of V. caven were scarified in 95–97%, analytical grade H₂SO₄ for 90 minutes and then hydrated in tap water overnight. Seeds of C. spinosa were scarified in 95–97%, analytical grade H₂SO₄ for 30 minutes and then hydrated in tap water overnight.

Germination

Activated seeds of Q. saponaria, P. chilensis, V. caven, and C. spinosa were placed in Petri plates over a filter paper bed (3 plates per species). Filter paper was then hydrated with distilled water. All plates were incubated in a crop chamber at 20°C, with light/dark cycles of 9 h/15 h. Germination is conditioned by temperature, so altering this factor could completely change the germination rates (Giuliani et al., 2015).

Plates were monitored periodically to count the germinated seeds and refill distilled water. Q. saponaria and P. chilensis plates were monitored until day 19 (Table 1). After that, fungal development made it difficult to check the plates, and a tactile examination of seeds indicated that most of them were rotten.

Plates containing V. caven and C. spinosa were more resistant to contamination and could be monitored until day 22. After this point, germination was too slow, and it was decided to end the experiment. Results are shown in Table 2.

The sample size, provided in the tables, is considered important for the replicability of a germination assay (Ribeiro-Oliveira & Ranal, 2016).

TG50 calculation

For Q. saponaria, P. chilensis and V. caven, the TG50 was linearly interpolated from the two closest points (Figure 1A–C). C. spinosa didn’t reach the 50% germination during the assay, so this was extrapolated using the last five points (Figure 1D). The TG50 of Q. saponaria was 4.9 days. P. chilensis had the fastest germination (TG50 = 1.7 days); V. caven had a TG50 of approximately 3.9 days, and the TG50 of C. spinosa was estimated to be 25.8 days.