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

Data on the germination rates of four tree species, natively founded in the Chilean Mediterranean-climate zone, were determined by germination in crop chambers. The obtained data were used to interpolate or extrapolate the time taken for 50% of seeds to germinate in each case. These results are useful for regional native forest research and, in a broad sense, for its use in models to study germination dynamics in Mediterranean-climate zones.

Introduction

Knowledge of the germination rates of a species means that future determination of this rate is unnecessary, preventing the waste of time and seeds.

Quillaja saponaria and Vachellia caven are two of the most representative trees in the Chilean Mediterranean forest ( Perez-Quezada & Bown, 2015), so information about these species will be useful for ecological investigation and restoration. Prosopis chilensis is vulnerable in the wild and is a key species of its community ( Valdivia & Romero, 2013); data about its propagation is important for conservation biologists.

In this article, we present the germination rates of seeds of Q. saponaria, P. chilensis, V. caven, and Caesalpinia spinosa. Dataset 1 contains the raw data from which these germination rates are calculated ( Plaza & Castillo, 2018).

Methods

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).

Table 1.

Percentage of germinated seeds of Q. saponaria and P. chilensis incubated for 19 days.

	Initial seeds per plate, n	Seeds germinated, %
		Day 0	Day 2	Day 5	Day 13	Day 19
Q. saponaria (n=3 plates)
Average	100	0.0	0.0	52.0	68.3	68.6
Standard Error	10	0.0	0.0	4.3	5.4	5.6
P. chilensis (n=3 plates)
Average	96	0.0	58.1	61.5	65.3	67.4
Standard Error	4	0.0	2.6	2.6	2.5	2.4

Table 2.

Percentage of germinated seeds of V. caven and C. spinosa incubated for 22 days.

	Initial seeds per plate, n	Seeds germinated, %
		Day 0	Day 2	Day 5	Day 7	Day 13	Day 19	Day 22
V. caven (n=3 plates)
Average	56	0.0	20.0	66.6	69.9	71.7	74.2	74.2
Standard error	5	0.0	3.3	1.9	1.4	1.5	1.9	1.9
C. spinosa (n=3 plates)
Average	61	0.0	0.0	17.1	32.5	44.8	48.0	48.5
Standard error	3	0.0	0.0	5.8	4.5	4.7	2.9	2.5

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 H 2SO 4 for 10 minutes and then hydrated in tap water overnight. Seeds of V. caven were scarified in 95–97%, analytical grade H 2SO 4 for 90 minutes and then hydrated in tap water overnight. Seeds of C. spinosa were scarified in 95–97%, analytical grade H 2SO 4 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 ).

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.

Also included are cumulative number of germinated seeds, percentages of germinated seeds and calculation of the TG50 for each species.

Click here for additional data file.

Data availability

The data referenced by this article are under copyright with the following copyright statement: Copyright: © 2018 Plaza  and Castillo M

Data associated with the article are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).

Dataset 1. Raw number of germinated seeds for each species, each repeat plate and each time point. Also included are cumulative number of germinated seeds, percentages of germinated seeds and calculation of the TG50 for each species. DOI: https://doi.org/10.5256/f1000research.16091.d216429 ( Plaza & Castillo, 2018).

Authors present germination data for four species from the Chilean Mediterranean forest. I would like to focus on the first statement of the introduction:

“Knowledge of the germination rates of a species means that future determination of this rate is unnecessary, preventing the waste of time and seeds”.

I think this statement is not accurate. Germination rate, especially in wild species, could be different depending on the cohort of seeds, the years of collection and the location. Data showed in this paper are valuable as a single biological replicate of germination behavior of the species used in the studies but it is necessary to add more biological replicates (different years and locations) to have a better understanding of germination behavior of the studied species.

Methods:

I would like to know from how many trees seeds were collected.

TG50 calculation could be more easily reproduced if the authors fit their data to a model (p/e sigmoid) and calculated first maximum derivate.

I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.

The authors conducted germination trials on seeds of four Chilean forest tree species. They indicate that this information could be useful for conservation and restoration studies. Regarding the methodology, the description of pretreatments and germination trials stands out. The study design is appropriate and the work is technically sound. I believe that the authors could increase the number of replicates (Petri plate), but in this case it is correct as a first approximation to determine the germination rates of Chilean forest tree seeds.

The manuscript represents a useful contribution to the theme of the germination of Chilean forest trees seeds and deserves to be indexed.

I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

The document provides valuable information on the germination rate of four native species. Quillaja saponaria and Vachellia caven are two of the most representative trees of the Chilean Mediterranean forest, Prosopis chilensis is in the category of threat and Caesalpinia spinosa adapts well to the conditions of the central zone of the country. The protocols for the collection of fruits and seeds, as well as the applied pre-germinative treatments, were based on methodologies recommended by the Centro de Semillas de la Universidad de Chile, CESAF Antumapu. Although they are described in the text, it would be convenient to add the references of Gold et al. (2004 [1]) and INFOR (2015 [2]) that complements the antecedents in pre-germination treatments for the species under study.

With regard to the results obtained, knowing the time required to achieve 50% of seed germination is a useful fact that helps to plan the work of plant reproduction for research and ecological restoration purposes as proposed by the authors.

I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.