Drying and storage of Piptadenia gonoacantha (Mart.) J.F.Macbr. seeds

Secagem e armazenamento de sementes de Piptadenia gonoacantha (Mart.) J.F.Macbr.

Abstract

The objective was to evaluate the sensitivity of Piptadenia gonoacantha seeds to desiccation and storage conditions. The seeds were subjected to artificial drying in a forced air convection oven (39.7 °C ± 0.78 and 28.1% ± 1.90 RH) for different periods. After each drying period, evaluation methods were performed to determine the seeds water content and germination (germination test). The seeds were divided into two lots in the storage experiment: with previous drying (at 6.0% water content) and without previous drying (control, at 11% water content), and were stored for 36 months in a plastic bag in three conditions: refrigerator at 5 °C, freezer at -20 °C and natural condition (29 °C). The seeds were removed every three months and subjected to water content measurement and germination tests. The reduction of the initial water content of the seeds from 14% to 6% upon artificial drying resulted in the loss of 1/3 of their viability, suggesting that the seeds are sensitive to desiccation. The best practice to store seeds of P. gonoacantha found in this study was without previous drying, into the freezer. The seeds lost only 14% of their germination after 36 months under these conditions.

Keywords:
intermediate; conservation; seed technology; forest seed

Resumo

O objetivo foi avaliar a sensibilidade de sementes de Piptadenia gonoacantha às condições de dessecação e armazenamento. As sementes foram submetidas à secagem artificial em câmara com circulação forçada de ar (39,7°C ± 0,78 e 28,1% ± 1,90 UR) por diferentes períodos. Após cada período de secagem, as sementes foram avaliadas quanto ao teor de água e à germinação. As sementes foram divididas em dois lotes no experimento de armazenamento: com secagem prévia (a 6,0% de teor de água) e sem secagem prévia (controle, a 11% de teor de água), e foram armazenadas por 36 meses em saco plástico em três ambientes: geladeira à 5 °C, freezer a -20 °C e ambiente natural (29 °C). As sementes foram retiradas a cada três meses e submetidas a aferição do teor de água e teste de germinação. A redução do teor inicial de água das sementes de 14% para 6% com a secagem artificial resultou na perda de 1/3 de sua viabilidade, sugerindo que a espécie seja sensível à dessecação. A melhor forma de armazenar as sementes de P. gonoacantha foi sem secagem prévia em freezer. Nestas condições, as sementes perderam somente 14% da germinação após 36 meses.

Palavras-chave:
intermediárias; conservação; tecnologia de sementes; semente florestal

1. Introduction

In response to the climate crisis and biodiversity loss, the UN has designated the decade from 2021 to 2030 as the Decade of Ecosystem Restoration. Several countries have committed to restoring millions of hectares of degraded land, including Brazil, which has set a goal of restoring 12 million hectares by 2030. Reversing degradation provides a range of environmental, social, and economic benefits, and has the potential to generate more than one-third of the necessary climate mitigation by increasing carbon storage and reducing greenhouse gas emissions (Griscom et al., 2017). One of the main obstacles in large restoration projects is the availability of seeds, which has hindered the use of germplasm from native species in habitat restoration (León‐Lobos et al., 2020; Jalonen et al., 2018). The high species diversity in restoration projects in tropical regions is limited by a lack of knowledge regarding seed biology, including minimum protocols for medium- and long-term conservation (Sommerville et al., 2018).

Seed storage is an effective method for ensuring seed availability throughout the year, not just during the harvest season. Drying seeds helps preserve their physiological state by reducing metabolism and respiration rates (Barrozo et al., 2014; Pelissari et al., 2022). While natural drying is the most used method, it is limited by climatic conditions; for example, drying seeds can be challenging under unfavorable relative humidity and temperature conditions or when dealing with large volumes (Garcia et al., 2004).

The duration and conditions of storage may vary according to the physiological behavior of each species in response to desiccation and low temperatures. Species are typically classified into three groups: (a) orthodox, which can be dehydrated to low water content (<5%) and stored at low temperatures; (b) intermediate, which tolerate desiccation up to 10-13% water content and show reduced viability at lower water content levels; and (c) recalcitrant, which do not withstand dehydration and suffer damage when stored at low temperatures (Roberts, 1973; Hong and Ellis, 1996). While this classification remains useful for management decisions, it does not address the wide spectrum of physiological responses to stress caused by desiccation and cooling (Barbedo, 2018).

Piptadenia gonoacantha (Mart.) J.F.Macbr. is a pioneer tree species from the Fabaceae family that can reach up to 20 meters in height and is found naturally in almost all Brazilian states, except Piauí, Maranhão, Amapá, and Roraima (Ribeiro and Queiroz, 2020). Commonly known as “pau-jacaré,” this species is widely used in forest restoration projects due to its rapid growth and association with Rhizobium and mycorrhizae (Bournaud et al., 2018). The flowers have high melliferous value, and its wood is prized for firewood, charcoal, interior finishing, and toy making, among other uses (Lorenzi, 1992). Flowering occurs from late October, with fruiting in September and October, producing dry, dehiscent fruits containing approximately seven seeds, which should be harvested when still green or green brown (Chitarra et al., 2008).

Carvalho (2004) stated that seeds of P. gonoacantha display recalcitrant storage behavior, with a short viability of up to 6 months in uncontrolled condition. Lorenzi (1992) further indicated that the viability of P. gonoacantha seeds in storage is limited, typically not exceeding 60 days. Mayrinck et al. (2016) classified P. gonoacantha as orthodox, although they reported a decrease in germination potential during the seed drying process. This study aims to evaluate the viability of P. gonoacantha seeds regarding their tolerance to desiccation and storage.

2. Material and Methods

2.1. Previous determination

Piptadenia gonoacantha seeds were collected from nine plants in September and October 2017 in the municipality of Silva Jardim, Rio de Janeiro, Brazil (22° 39’ 34” S, 42° 22’ 57” W, altitude 50 m, average annual temperature of 23 °C, average annual precipitation of 2283 mm). The fruits were collected with a brown color, but still closed. They were processed and then sent to the Embrapa Agrobiology Laboratory (Seropédica, RJ), where the seeds damaged by insects were identified and discarded. After processing, a lot of seeds was formed for the experiments with approximately 30,500 seeds, and for which the weight of a thousand seeds, the number of seeds per kilogram and water content were determined, according to the methodology proposed by Brasil (2009).

2.2. Drying experiment

The seeds were dried in an oven with forced air circulation at 40 °C for different periods: 0 (control), 1, 2, 4, 5, 6, 8, 10, 12, 24, 48 and 264 hours. Using a thermohygrograph, the temperature and humidity of the oven were recorded every hour during the period of the drying experiment (from October 24, 2017 to November 5, 2017). The average temperature and relative humidity of the forced air convection oven were 39.7 °C ± 0.78 and 28.1% ± 1.90, respectively.

After being subjected to each drying period, the seeds were removed from the forced air convection oven and evaluated for water content and germination. The water content of the seeds was measured using the oven method at 105 ± 3 °C for 24 hours, with three sub-samples of 5 g (±70 seeds) each (Brasil, 2009). Seed germination was evaluated in four replications of 25 seeds, in a test conducted on paper with two sheets of filter paper in a petri dish moistened with 3 ml of water. The plates were randomly arranged in Biochemical Oxygen Demand B.O.D. germinators at a constant temperature of 25 °C, with a 12-hour photoperiod (Brasil, 2009). Previously to the germination test, the seeds were disinfected for 30 seconds in alcohol 70%, followed by 5 minutes in 1% sodium hypochlorite and washed four times in distilled water (Brasil, 2009).

Germination was evaluated every three days in the first two weeks and then weekly until germination stabilization. The number of germinated seeds (considering the biological criterion of radicle emission with a minimum size of 2 mm), the number of dead seeds, the number of normal and abnormal seedlings were recorded. The Germination Speed Index was calculated from the number of seeds germinated over time (Maguire, 1962).

Germination percentage and water content were tested for normality and homogeneity of the residual variance of the adopted statistical model (p≤0.05). After meeting these assumptions for carrying out the analysis of variance and when there was a significant difference between the drying time levels using the F test of the analysis, the data were fitted to the exponential regression model considering a 5% probability of significance. The R Program (R Core Team, 2022) was used in statistical analyzes. A Spearman correlation analysis was conducted between the seed water content and germination variables, based on the results obtained from the drying experiment.

2.3. Storage experiment

The seed storage experiment was installed in December 2017, testing the following six treatments: a) DSNC - dry seeds stored in a natural condition in the laboratory (28.9 °C ± 3.6; 51.9% RH ± 9.4); b) DSR - dry seeds stored in a refrigerator (4.31±1.8 °C; 32.2% RH ±6.5); c) DSF - dry seeds stored in a freezer (-20 °C); d) MSNC - non-dried (moist) seeds stored in a natural condition in laboratory; e) MSR - non-dried seeds stored in the refrigerator; and f) MSF - non-dried seeds stored in the freezer.

The previous drying of the seeds was performed in a convection oven at 40 °C for 120 hours until approximately 6% water content was reached. The seeds were placed in a 0.5 mm thick plastic bag for storage, with each treatment containing approximately 325 seeds. The seeds were evaluated at zero storage time (control) and at 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33 and 36 months of storage in relation to seed water content and germination, following the drying experiment methodology. The experimental design was completely randomized, with 4 replications of 25 seeds each and 74 treatments, corresponding to a factorial of 2x3x12+2 controls. The three factors evaluated were the previous drying of the seeds (without and with), the seed storage condition (natural, refrigerator and freezer) and their storage times (3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33 and 36 months) combined into 72 treatments plus 2 controls in which the seeds were evaluated prior to storage, with and without previous drying of the seeds.

Germination data (%), Germination Speed Index (GSI) and seed water content (%) evaluated over the storage months were tested using a Generalized Linear Model (GLM) with negative binomial distribution and log link function. The significance between treatments, the interaction between the factors drying, condition and storage time and these factors alone were verified by the Chi-Squared test (χ²<0.05) using the deviance analysis (ANODEV). The means estimated by the negative binomial model were compared using the Tukey’s test and regression models were adjusted to the data to evaluate storage times for each combination of the other two factors. All statistical analyzes were performed using the R software program (R Core Team, 2022) at 5% probability.

3. Results

3.1. Drying

The average weight of a thousand P. gonoacantha seeds was 66.58 g ± 15.36, presenting an average of 15,715 ± 3,290 seeds per kilo. The lot of P. gonoacantha seeds had an initial germination power of 79% and a water content of 13.9%.

At different drying times, the water content and germination percentages of the seeds were as follows: no drying: 13.84%, 78%; 1 hour: 12.66%, 81.00%; 2 hours: 12.76%, 79.00%; 3 hours: 10.91%, 67.00%; 4 hours: 11.53%, 76.00%; 5 hours: 11.44%, 77%; 6 hours: 11.94%, 76.00%; 8 hours: 12.39%, 69.00%; 10 hours: 10.70%, 61.00%; 12 hours: 11.13%, 62.00%; 24 hours: 10.65%, 65.00%; 48 hours: 7.67%, 54.00%; 264 hours: 5.99%, 50.00%. It is noted that the reduction in germination began early in the drying process, as the water content decreased from 13.8% to 10.7%, resulting in a 17% loss in germination.

Drying the seeds of P. gonoacantha for 264 hours (T12) reduced the water content from 13.84% to 5.99%. This reduction resulted in a 28% loss of the germination potential, which decreased from 78% to 50%. The correlation between water content and germination was positive, high and significant (r = 0.84; p=0.0003) – Figure 1.

Figure 1
Correlation between germination and water content of P. gonoacantha seeds subjected to different drying periods in an oven at 40°C.

The percentage of germination, water content, and Germination Speed Index (GSI) declined exponentially with drying up to 48 hours, tending to stabilize from this point onward with increasing drying time (Figure 2).

Figure 2
Exponential model fitted significantly (p<0.05) to water content (A), germination data (B) and Germination Speed Index (C) of Piptadenia gonoacantha seeds, with coefficient of determination (adj.R²).

The maximum germination percentage estimated by the exponential model at drying time 0 was 79%, and the minimum was 51% at 264 hours, tending to stabilize from then on. The maximum estimated by the model for water content was 12.7% at drying time 0, and the minimum was 5.9% at 199 hours, also tending to stabilize after this number of hours (Figure 2).

3.2. Storage

The stored seeds subjected to previous drying had an initial water content of 6.16%, while those without previous drying had an initial water content of 11.34%. There was a significant difference between the storage condition for the water content of seeds subjected to previous drying, with higher values in the natural condition (DSNC) in relation to the other storage conditions (refrigerator and freezer). There was no difference in the water content of seeds with previous drying between the freezer (MSF) and the refrigerator (MSR) – Table 1.

Table 1
Average values and standard error of water content (%) and germination speed index of Piptadenia gonoacantha seeds stored at room temperature (Natural), refrigerator and freezer, with and without previous drying, averaged over the evaluated time periods.

Previous drying	Storage conditions			General mean
	Natural	Refrigerator	Freezer
	Water content (%)
With	10.87±0.86 aA	7.69±0.40 bB	6.71±0.44 bB	8.42±1.08B
Without	11.70±0.37 aA	10.48±0.43 aA	10.34±0.33 aA	10.84±0.48A
General mean	11.28±0.70 a	9.09±0.82 b	8.52±1.00 b	9.63±1.03
	Germination Speed Index
With	0.30±0.31 bA	2.12±0.33 aB	2.24±0.39 aB	1.55±0.56 B
Without	0.11±0.17 bB	2.79±0.52 aA	3.53±0.40 aA	2.14±0.84 A
General mean	0.20±0.26 b	2.45±0.46 a	2.88±0.50 a	1.85±0.72

• Means followed by different letters, lowercase in the line (between seed storage conditions) and capital letters in the column (between with and without seed drying) in each drying time and average of drying times, differ from each other using the Tukey’s test at 5% probability.

The water content of the seeds with previous drying after 36 months of storage in a natural condition increased from 6.16% to 12.95%, with an average of 10.87 ± 2.15%. Due to the greater variation in temperature and relative humidity conditions in this local, there was no significant difference between the water content of seeds with and without previous drying, and the water content between drying treatments became equal throughout of the experiment (Table 1). The increase in water content was smaller in the controlled condition of the refrigerator (Refrigerator CS) and freezer (Freezer CS), reaching up to 7.94% and 6.23% at the end of the experiment, respectively. There was a significant difference for the drying treatment for these conditions (Table 1).

Seeds that did not undergo previous drying (initial content of 11.34%) had similar water content between storage conditions, but occurred variation in water content in the natural condition (MSNC), reaching 12.68% at end of the experiment. The seeds stored in the refrigerator (MSR) and freezer (MSF) reached the end of the experiment with a lower water content than the initial one, with 10.12% and 10.21%, respectively.

In the natural condition, the seeds subjected to drying showed a higher GSI than those that were not dried. In the controlled condition of the refrigerator and freezer, the best results were found for seeds that were not dried compared to dried seeds (Table 1). There was no difference in the GSI of the non-dried seeds stored in the freezer and those stored in the refrigerator.

Germination at the beginning of storage was 50% for seeds with previous drying and 83% for seeds without previous drying. A reduction in the germination percentage of P. gonoacantha seeds was observed after drying and throughout the storage time.

Although drying reduced seed germination, it increased storage time in the natural condition. Seeds without previous drying (MSNC) completely lost viability after 9 months stored in the natural condition, while the decline in germination was less pronounced for seeds with previous drying (DSNC), with total loss at 12 months. The seeds stored in the refrigerator, both with and without previous drying, ended the experiment with around 20% germination. However, considering that the initial viability was 50% for seeds with previous drying and 83% without previous drying, the total storage loss was greater in seeds not subjected to previous drying.

The seeds without drying performed better in the freezer (MSF), with an initial germination of 83% and a reduction to 69% after 3 years of storage, meaning a loss of only 14%. Seeds with previous drying stored in the freezer (MSF), which started the experiment with 50% germination, lost 26% of their viability in 3 years, reaching 24% of germination at the end of the experiment (Table 2).

Table 2
Average germination (%) and standard error values of Piptadenia gonoacantha seeds stored at room temperature (Natural), refrigerator and freezer, with and without previous drying, after 36 months.

Time (months)	Previous drying	Storage conditions
		Mean Germination (%)
		Natural	Refrigerator	Freezer
3	With	61±10 aA	63±3.5 aA	51±7 aB
	Without	66±5.5 aA	81±2.5 aA	75±4 aA
6	With	37±4 aA	36±7 aB	52±6 aB
	Without	26±10.5 bA	62±5.5 aA	76±4 aA
9	With	21±5.5 bA	59±6 aA	64±4 aA
	Without	1±1 bB	67±5 aA	81±4.5 aA
12	With	0±0 bA	52±4 aA	58±4 aA
	Without	0±0 bA	51±8.5 aA	73±11 aA
15	With	2±1 bA	33±3.5 aB	39±6.5 aB
	Without	1±1 bA	67±4.5 aA	74±5 aA
18	With	1±1 bA	53±6 aA	51±10.5 aA
	Without	0±0 bB	55±15 aA	68±6.5 aA
21	With	0±0 bA	59±2.5 aA	46±9 aA
	Without	0±0 bA	62±6.5 aA	55±2.5 aA
24	With	0±0 bA	49±5.5 aA	39±4 aB
	Without	0±0 bA	47±5.5 aA	66±5 aA
27	With	0±0 bA	45±5 aA	60±5 aA
	Without	0±0 bA	46±7.5 aA	67±2.5 aA
30	With	0±0 bA	54±7.5 aA	39±6.5 aB
	Without	0±0 cA	43±3 bA	68±6.5 aA
33	With	0±0 bA	50±11.5 aA	41±9.5 aB
	Without	0±0 cA	36±5 bA	73±8.5 aA
36	With	0±0 bA	22±5.5 aA	24±5.5 aB
	Without	0±0 cA	20±3 bA	69±5 aA

• Means followed by different letters, lowercase in the line (between seed storage conditions) and capital letters in the column (between with and without seed drying) in each drying time and average of drying times, differ from each other using the Tukey’s test at 5% probability.

There was no significance for germination between the evaluation times for the refrigerator with drying (MSR) and freezer without drying (MSF) treatments (p>0.05). In the first case, it is observed that the seeds stored in this condition lost their viability over time, but the lack of significance was probably related to the high coefficient of variation of the data. In the case of the freezer, the lack of significance was related to maintained seed viability in this condition. There were significant fits (p≤0.05) of the negative binomial regression models for the other combinations between storage condition and type of drying (with and without) (Figure 3). It is possible to estimate that there was a reduction in seed germination for each month that passes with such models, constituting 1.41% for the natural condition with drying treatment (DSNC); 1.02% for freezer with drying (DSF); 1.59% for natural condition without drying (MSNC) and 1.03% for freezer without drying (MSF).

Figure 3
Fitting of Regression Models to Piptadenia gonoacantha seed germination data over 36 months, stored with and without previous drying in different storage conditions. Legend: MSNC – moist seed (non-dried) natural condition; DSNC – dry seeds natural condition; MSR – moist seed (non-dried) refrigerator; DSR – dry seeds refrigerator; MSF – moist (non-dried) seed freezer; DSF – dry seed freezer. n.s. - not significant.

4. Discussion

The results indicated that P. gonoacantha seeds were sensitive to water loss. The seeds lost 28% of germination (from 78% to 50%) when the water content of the seed reduced from 14% to 6% with desiccation. However, it was not necessary to reach 6% water content to observe a loss in germination, as a significant decline in germination potential was already evident with a reduction to 10% water content. The loss of water in seeds sensitive to desiccation can trigger processes such as protein denaturation, changes in the activity of peroxidase enzymes and damage to the membrane system, resulting in a complete loss of viability (Castro et al., 2017; Martins et al., 2019; Tian et al., 2019). Desiccation damage is also associated with the compression of cell constituents due to cell shrinkage (Walters et al. 2002; Walters and Koster 2007), with a loss of more than 50% of volume considered lethal to cells (Meryman, 1974).

Several factors can influence seed drying tolerance. Among them, we can mention the fruit maturation stage (Barbedo et al., 2013; Leprince et al., 2017; Xue and Wen, 2018), the drying speed (Coelho et al., 2017; Alves et al., 2017), the drying time (Nugraheni and Yuniarti, 2022), and even the origin of the seeds (Pereira et al., 2017). Immature fruits may respond differently to drying than fruits collected “ripe”, as they have a high water content in the seeds and they may suffer a considerable reduction in cell volume when dried, which in turn may be accompanied by a simultaneous removal of the membrane seed cell wall (Xue and Wen, 2018; Oliver et al., 2020). The accumulation of dry matter reserves during embryonic development is a major cause of structural and compositional changes in cells and has important protective benefits during desiccation and storage (Nadarajan et al., 2023). During the maturation process, proteins are produced that perform protective functions involved in desiccation tolerance, among which the Late Embryogenesis Abundant (LEA) proteins stand out. Although their function is not yet fully understood, numerous studies have shown that these proteins are involved in complex processes that allow seeds to survive in a dry state, through glass formation and cryoprotection mechanisms (Shih et al., 2008). Mescia et al. (2022) observed an increase in starch content and a decrease in soluble sugars during the maturation process of Paubrasilia echinata (Brazilwood) seeds, which probably contributed to greater tolerance to desiccation.

Studies carried out by Chitarra et al. (2008) classified P. gonoacantha fruits into three maturation stages: green, green-brown and brown, with water content of 70%, 41% and 14%, respectively. Since it is an anemochorous species, P. gonoacantha is normally collected with the fruits still closed before they open and disperse, which occurred in this study. P. gonoacantha fruits were harvested green-brown to brown and the seeds were found to contain 14% of water after undergoing natural pre-drying (exposure to the environment). Corroborating the results of P. gonoacantha sensitivity to desiccation observed in this study, Chitarra et al. (2008) and Mayrinck et al. (2016) also observed that seeds of P. gonoacantha that underwent the drying process had lower germination rates compared to freshly harvested seeds.

The P. gonoacantha seeds were dried at 40 °C in a forced air circulation oven. The maximum temperature for safe drying depends on the species, but generally varies from 35 to 45 °C. This temperature can be higher when the seeds are already partially dry (Harrington, 1972). For example, it was reported that drying Talisia esculenta Radlk seeds at different controlled temperatures (40, 45 and 50 °C) reduced the germination percentage and vigor, with the species being classified as recalcitrant (Cardoso et al., 2015). Clitoria fairchildiana Engler. seeds, with an initial water content of 23%, were subjected to drying at four temperatures (35, 40, 45 and 50 °C) for five periods (0, 6, 12, 18 and 24 hours) (Alves et al., 2015). The authors concluded that the species is sensitive to desiccation, and that drying at 35 °C for 6 hours can be carried out without affecting its viability.

Although drying reduced the germination of P. gonoacantha seeds, it extended the storage time of the seeds in the natural condition from 9 to 12 months compared to non-dried seeds. Freire et al. (2020) also observed that drying extended the storage time of Melanoxylon brauna Schott seeds from 12 to 16 months in natural condition. García et al. (2006) observed that the germination capacity of Paubrasilia echinata seeds was better maintained in refrigerated storage in comparison to the natural condition. The authors noted that in the natural condition, the seeds lasted only 1 month and reported a significant reduction in the proportions of glucose and fructose, which was associated with the loss of germinability in the natural condition.

The seeds of P. gonoacantha exhibited high variation in germination results during the storage experiment, with a high standard error in both dry and non-dry seeds (see standard error in Table 2). One factor that may have contributed to this was fungal contamination during the germination tests. Despite the aseptic procedures implemented, numerous fungi appeared as the seeds began to germinate. For this reason, we did not use data from normal seedlings in the germination tests, as many seedlings were completely contaminated. Even with this variation, significant and consistent differences were observed in the tested treatments of pre-drying and conditions storage, with interactions between these factors. The best storage conditions were found to be freezing without drying. For these treatment, the regression analysis over time was not significant, indicating that there was no loss of germination potential after 36 months of storage. Some studies have demonstrated that drying can be beneficial for storage under ambient conditions, but not for storage at subzero temperatures (Hong et al., 2005; Wawrzyniak et al., 2020). Below a critical water content level, seed longevity may not further increase with drying (Walters, 2007).

Based on the data presented in this study, it can be confidently asserted that seeds of P. gonoacantha does not exhibit recalcitrant behavior, as suggested by Carvalho (2004) and Lorenzi (1992). After 3 years of storage in the freezer, the seeds without previous drying lost only 14% of their germination (a reduction from 83% to 69%), making this the best condition for maintaining their viability. It also does not show typical orthodox behavior, once it shows a reduction in germination power at a high water level (between 10 and 14%).

It is suggested that the seeds of P. gonoacantha exhibit a behavior that more closely resembles that of intermediate seeds. Walters (2015) highlights that intermediate conditions can manifest in various forms, including: (1) seeds that can tolerate drying to lower moisture levels than recalcitrant seeds, but not as low as orthodox seeds; (2) seeds that exhibit anomalous longevity responses at temperatures between +10 and -30 °C; or (3) seeds that have a short lifespan, regardless of how they are dried or cooled. In this context, we suggest an intermediate behavior for P. gonoacantha, related to germination damages caused by seed drying. The preservation of seed viability during storage at subzero temperatures is uncommon among intermediate species (Scandé et al., 2000; Gomes et al., 2013; Joshi et al., 2015) but can occur (León-Lobos and Ellis, 2002). According to Hong and Ellis (1996), species with intermediate storage behavior adapted to tropical environments should be differentiated from those adapted to temperate environments, including those found at high altitudes in the tropics. The natural occurrence of P. gonoacantha ranges from 10 m to 1,300 m in altitude, being found in climates classified as tropical (Af and Aw), subtropical highland (Cwa and Cwb), humid subtropical (Cfa), and humid temperate (Cfb) (Carvalho, 2004).

In summary, this study developed a long-term method for storing seeds of P. gonoacantha. The species was better preserved in the freezer without previous drying, maintaining its viability under these conditions for at least 36 months. The results provide useful information to support the use of this species in restoration efforts and may serve as a reference for the storage of seeds of other non-dormant leguminous species that share similarities with the studied species.

Acknowledgements

To Nelson Barbosa and the Mico Leão Dourado Association for collecting and processing the P. gonoacantha seeds. To Marcelo Antoniol from the Legumes Laboratory at Embrapa Agrobiologia for the support in the laboratory.

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Publication Dates

• Publication in this collection
  27 Jan 2025
• Date of issue
  2024

History

• Received
  08 May 2024
• Accepted
  28 Oct 2024