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Drying kinetics and physiological quality of Solanum aethiopicum seeds 1 1 Research developed at Universidade Federal de Viçosa, Departamento de Agronomia, Viçosa, MG, Brazil

Cinética de secagem e qualidade fisiológica de sementes de jiló

ABSTRACT

The drying process is paramount for maintaining seed quality, where the temperature during this process directly influences germination and vigor, especially for vegetable species harvested with high moisture content. This research aimed to determine and model the drying curves of S. aethiopicum (cultivar Tinguá-verde-claro) seeds at temperatures of 35, 38, 41, and 44 ºC, as well as to evaluate the physiological quality of the seeds after drying. A completely randomized design was used, with four drying temperatures (35, 38, 41, and 44 ºC) and four replicates. Nine mathematical models were fitted using the non-linear regression analysis by the Gauss-Newton method, and the goodness of fit was assessed based on the magnitude of the coefficient of determination (R2), chi-square test (χ2), relative mean error (P), and estimated mean error (SE). Seed quality was evaluated by germination test (G), electrical conductivity (EC), and accelerated aging (AA). The Modified Midilli model best represents the drying curves of S. aethiopicum seeds at the studied temperatures. Seeds with higher germination and vigor, meaning lower electrical conductivity values and higher germination rates after accelerated aging, are achieved through drying at 35 and 38 ºC.

Key words:
mathematical modeling; germination; vigor

RESUMO

O processo de secagem é de suma importância para a manutenção da qualidade das sementes, onde a temperatura de condução deste processo exerce influência direta sobre a germinação e vigor, sobretudo para as espécies olerícolas que são colhidas com alto teor de água. O objetivo desta pesquisa foi determinar e modelar as curvas de secagem de sementes de jiló (cultivar Tinguá-verde-claro) nas temperaturas de 35, 38, 41 e 44 ºC, bem como avaliar a qualidade fisiológica das sementes após a secagem. Foi utilizado o delineamento inteiramente casualizado, sendo quatro temperaturas de secagem (35, 38, 41 e 44 ºC) com quatro repetições. Nove modelos matemáticos foram ajustados por meio de análise de regressão não linear pelo método de Gauss-Newton, e o grau de ajuste foi avaliado com base na magnitude do coeficiente de determinação (R2), teste qui-quadrado (χ2), erro médio relativo (P) e erro médio estimado (SE). A qualidade das sementes foi avaliada pelo teste de germinação (G), condutividade elétrica (CE) e envelhecimento acelerado (EA). O modelo ‘Midilli Modificado’ é o que melhor representa as curvas de secagem das sementes de jiló nas temperaturas estudadas. Sementes com maior germinação e vigor, ou seja, com menores valores de CE e maiores taxas de germinação após EA, são alcançadas através da secagem a 35 e 38 ºC.

Palavras-chave:
modelagem matemática; germinação; vigor

HIGHLIGHTS:

The Modified Midilli model can be used to estimate the drying curves of S. aethiopicum seeds.

S. aethiopicum seeds dried at 35 and 38 ºC show higher germination and vigor.

Drying at 41 and 44 ºC impairs the physiological quality of S. aethiopicum seeds.

Introduction

Solanum aethiopicum, a member of the Solanaceae family, produces initially green fruits that ripen into an orange-red hue (Santos et al., 2020Santos, S. G. F. D.; Sarti, J. K.; Kran, C. D. S.; Silva, H. W.; Rodovalho, R. S.; Vale, L. S. R.; Devilla, I. A. Desorption isotherms and thermodynamic properties of Solanum gilo. Australian Journal of Crop Science, v.14, p.1810-1816, 2020. https://search.informit.org/doi/10.3316/informit.800751957981936
https://search.informit.org/doi/10.3316/...
). In Brazil, its cultivation is predominantly concentrated in the southeastern states, with Rio de Janeiro notably leading as the primary producer, contributing 32% to the national yield (Pinheiro et al., 2015Pinheiro, J. B.; Pereira, R. B.; Freitas, R. A.; Melo, R. D. C. A cultura do jiló. 1 ed. Brasília: Embrapa , 2015. 70p.). Its fruits are nutrient-rich, including various vitamins (A, B, and C), minerals, and flavonoids (Alcântara & Porto, 2019Alcântara, H. P.; Porto, F. G. M. Influência de fertilizante foliar com aminoácidos na cultura do jiló. Brazilian Journal of Development, v.5, p.5554-5563, 2019. https://doi.org/10.34117/bjdv5n6-087
https://doi.org/10.34117/bjdv5n6-087...
).

Seeds of fleshy fruits, such as those of S. aethiopicum, exhibit high moisture levels, exceeding 40% post-physiological maturity, making them prone to deterioration, thus reducing their quality (Guragain et al., 2023Guragain, R. P.; Baniya, H. B.; Pradhan, S. P.; Pandey, B. P.; Shrestha, B.; Fronczak, M. Growth enhancement of radish seed induced by low-temperature argon plasma. Chemistry and Plasma Processing, v.43, p.111-137, 2023. https://doi.org/10.1007/s11090-022-10291-x
https://doi.org/10.1007/s11090-022-10291...
). Hence, the drying process is pivotal for preserving seed quality, eliminating excess free water, curbing biological activity, and ensuring germination viability. Improper drying induces adverse physiological effects in seeds, including alterations in enzymatic activity, protein denaturation, and cellular damage, impairing germination (Rosa et al., 2023Rosa, C. O.; Silva, F. A.; Cruz, D. R. C.; Santos, S. G. F. Importância da secagem e armazenamento adequados na manutenção da qualidade de sementes de pimenta (Capsicum). Research, Society and Development, v.12, p.1-14, 2023. http://dx.doi.org/10.33448/rsd-v12i8.43000
http://dx.doi.org/10.33448/rsd-v12i8.430...
). This study hypothesizes that drying at high temperatures may reduce the physiological quality of S. aethiopicum seeds.

Silva et al. (2018Silva, H. W. D.; Vale, L. S.; Silva, C. F.; Souza, R. D. C. Drying kinetics and physiological quality of ‘Cabacinha’ pepper seeds during storage. Revista Brasileira de Engenharia Agrícola e Ambiental , v.22, p.292-297, 2018. https://doi.org/10.1590/1807-1929/agriambi.v22n4p292-297
https://doi.org/10.1590/1807-1929/agriam...
) found that ‘Cabacinha’ pepper seeds dried at 35 and 38 ºC exhibited higher germination and vigor, but drying at 42 ºC reduced seed quality. Similar results were found for tomato seeds (Gomes et al., 2023Gomes, G. P.; Queiroz, R. A.; Takahashi, L. S. A. Potencial fisiológico de sementes de tomate orgânico e convencional. Revista Terra & Cultura: Cadernos de Ensino e Pesquisa, v.39, p.1-12, 2023. ). However, there are no studies on the ideal drying temperatures for S. aethiopicum seeds. Furthermore, studies related to mathematical modeling and kinetics of seed drying are highlighted to optimize drying processes, reduce costs, and enhance dryer design (Alves et al., 2022Alves, J. C. R.; Ferreira Júnior, W. N. F.; Santos, S.; Almeida, V. G.; Vaz, V.; Selari, P. J.; Rodovalho, R. S. Cinética de secagem e propriedades termodinâmicas de sementes de Capsicum baccatum L. var. pendulum (Willd.) Eshbaugh. Revista de Ciências Agrárias, v.45, p.34-43, 2022. https://doi.org/10.19084/rca.27148
https://doi.org/10.19084/rca.27148...
; Arsenoaia et al., 2023Arsenoaia, V. N.; Roșca, G. R.; Cârlescu, P.; Băetu, M.; Rațu, R. Drying process modeling and quality assessments regarding an innovative seed dryer. Agriculture, v.13, p.328-345, 2023. https://doi.org/10.3390/agriculture13020328
https://doi.org/10.3390/agriculture13020...
).

Therefore, this research aimed to determine and model the drying curves of S. aethiopicum (cultivar Tinguá-verde-claro) seeds at temperatures of 35, 38, 41, and 44 ºC, as well as to evaluate the physiological quality of the seeds after drying.

Material and Methods

The study was conducted at the Seed Analysis Laboratory (LAS) of the Universidade Federal de Viçosa, located in Viçosa, Minas Gerais state, Brazil (20° 44’ 35” S and 42° 52’ 33” W), between March and July of 2023. The fruits of S. aethiopicum, cultivar Tinguá Verde-Claro, were harvested at full maturity (completely red), and their seeds were manually extracted. It is worth mentioning that, before extraction, the fruits were left to rest for seven days under laboratory conditions to standardize the ripening stage and facilitate seed extraction.

Following extraction, the seeds underwent natural pre-drying under laboratory conditions (mean values = 25.8 ºC temperature and 68.8% relative air humidity) for 48 hours, reaching a moisture content of approximately 29% (wet basis). It should be emphasized that the moisture content was monitored using gravimetry and compared with the oven method at 105 ºC for 24 hours (BRASIL, 2009BRASIL. Ministério da Agricultura, Pecuária e Abastecimento - Regras para análise de sementes. Brasília: MAPA, 2009. 395p. ).

Subsequently, the seeds were dried in a forced circulation oven at 35, 38, 41, and 44 ºC. The seeds were dried until the appropriate moisture content (7% kg-1 of dry weight) for storage of vegetable seeds in airtight containers, as recommended by Melo et al. (2014Melo, A. M. T.; Nascimento, W. M.; Freitas, R. A. Produção de sementes de pimenta. In: Nascimento, W. M. Produção de sementes de hortaliças. Brasília: Embrapa. 2014. Cap. 6, p.169-197.). For this purpose, three replications of approximately 5 g of seeds were arranged in metal trays (7.30 × 2.00 cm) in a single layer. The moisture content of the seeds was monitored using gravimetry, weighing the seeds periodically on an analytical balance (precision of 0.0001 g).

The calculation of the moisture content ratio (RX) during the drying processes was performed using Eq. 1:

R X = X - X e X i - X e (1)

Where:

RX - moisture content ratio, dimensionless;

X - seed moisture content, kg water kg-1 dry mass;

Xe - equilibrium moisture content of seeds, kg water kg-1 dry mass; and,

Xi - initial seed moisture content, kg water kg-1 dry mass.

The Modified Oswin model (Eq. 2) was used to calculate the equilibrium moisture content of the seeds under each drying condition, whose values were 6.73, 5.82, 4.77, and 4.00%, respectively, for temperatures of 35, 38, 41, and 44 ºC and relative air humidity of 29.4, 26.7, 21.4, and 19.2%. This model was recommended by Santos et al. (2020Santos, S. G. F. D.; Sarti, J. K.; Kran, C. D. S.; Silva, H. W.; Rodovalho, R. S.; Vale, L. S. R.; Devilla, I. A. Desorption isotherms and thermodynamic properties of Solanum gilo. Australian Journal of Crop Science, v.14, p.1810-1816, 2020. https://search.informit.org/doi/10.3316/informit.800751957981936
https://search.informit.org/doi/10.3316/...
) to estimate the hygroscopic equilibrium curves of S. aethiopicum seeds.

X e = 18 . 7511 * * - 0 . 2931 * * T a w 1 - a w 1 3 . 7745 * * (2)

Where:

Xe - equilibrium moisture content, % dry basis (d.b.);

aw - water activity, decimal; and,

T - temperature, °C.

Nine mathematical models were fitted to the experimental moisture content ratio data (Silva et al., 2018Silva, H. W. D.; Vale, L. S.; Silva, C. F.; Souza, R. D. C. Drying kinetics and physiological quality of ‘Cabacinha’ pepper seeds during storage. Revista Brasileira de Engenharia Agrícola e Ambiental , v.22, p.292-297, 2018. https://doi.org/10.1590/1807-1929/agriambi.v22n4p292-297
https://doi.org/10.1590/1807-1929/agriam...
; Oliveira et al., 2021Oliveira, D. E.; Guimarães, J. M.; Bueno, S. G. S.; Costa, J. R.; Alves, E. M.; Silva, B. M. S. Drying kinetics of pumpkin seeds. Comunicata Scientiae, v.12, p.1-8, 2021. https://doi.org/10.14295/cs.v12.3391
https://doi.org/10.14295/cs.v12.3391...
), represented in Table 1.

Table 1
Non-linear regression models used to estimate the drying phenomenon of S. aethiopicum seeds

The criteria initially used to assess the fitting quality of the models were the coefficient of determination (R2), estimated mean error (SE), relative mean error (P), and the chi-square test (χ2). The SE, P, and χ2 values were calculated using Eqs. 12, 13, and 14, respectively.

S E = i = 1 n Y - Y ^ 2 D F (12)

P = 100 n i = 1 n Y - Y ^ Y (13)

χ 2 = i = 1 n Y - Y ^ 2 D F (14)

Where:

n - number of experimental observations;

Y - experimental moisture content ratio;

Ŷ - predicted moisture content ratio;

DF - degrees of freedom of the model.

Additional criteria were employed to select a single model that more accurately describes the drying process of S. aethiopicum seeds. For the models that showed the best fit according to the previously listed criteria, the Akaike Information Criterion (AIC) and the Bayesian Information Criterion (BIC) were calculated using Eqs. 15 and 16, respectively.

A I C = - 2 log l i k e + 2 p (15)

B I C = - 2 log l i k e + 2 p ln n (16)

Where:

p - number of parameters of the model;

n - total number of observations;

loglike - value of the logarithm of the likelihood function considering the estimates of the parameters.

In choosing the best mathematical model, considerations were made for the R² closest to the magnitude, P values below 10%, standard error (SE), and χ² values closer to zero, in addition to the lowest values of AIC and BIC.

After drying at each temperature, the seeds were placed in airtight plastic containers and stored in a refrigerator (T = 9.9 ºC and RH = 70%) for one day. The following tests were conducted to assess physiological quality:

Germination test: four replications of 50 seeds were placed in germination boxes (gerbox). The seeds were sown on two sheets of seed germination paper moistened with distilled water at 2.5 times the weight of the dry paper. The boxes were placed in a germinator at a constant temperature of 30 ºC. Evaluations were conducted at 6 (first count) and 14 days (last count) after the test was set up, considering the normal seedlings and the results expressed in % (BRASIL, 2009BRASIL. Ministério da Agricultura, Pecuária e Abastecimento - Regras para análise de sementes. Brasília: MAPA, 2009. 395p. ).

Electrical conductivity test: four replications of 50 intact seeds were weighed on a precision scale. The seeds were placed in disposable cups with 25 mL of distilled water. The cups with the seeds and water were placed in a germination chamber (B.O.D.) at 25 ºC for 24 hours. Subsequently, the electrical conductivity of the seed-soaking solution was measured using a conductivity meter, and the results were expressed in µS cm-1 g-1 (Vieira & Krzyzanowski, 1999Vieira, R. D.; Krzyzanowski, F. C. Teste de condutividade elétrica. In: Krzyzanowski, F. C.; Vieira, R. D.; França, J. B. Vigor de sementes: Conceitos e testes. Londrina: Abrates , 1999. Cap 1, p.41-42.).

Accelerated aging: four replications of 3 g of seeds were used for each treatment. The seeds were laid out in a single layer and distributed over a plastic screen fixed inside a germination box containing 40 mL of sodium chloride (NaCl) solution at the bottom (40 g NaCl 100 mL-1 of water). The covered boxes were placed in a B.O.D. chamber at 41 ºC for 48 hours (Alves et al., 2012Alves, C. Z.; Godoy, A. R.; Candido, A. C. S.; Oliveira, N. C. Qualidade fisiológica de sementes de jiló pelo teste de envelhecimento acelerado. Ciência Rural, v.42, p.58-63, 2012. http://dx.doi.org/10.1590/s0103-84782012000100010
http://dx.doi.org/10.1590/s0103-84782012...
). After this period, the seeds were allowed to germinate according to the methodology described for the germination test, and the number of normal seedlings was assessed six days after the test was set up, with the results expressed in percentage (%).

The design used was completely randomized, with four treatments and four replicates. The data was assessed for normality and homogeneity of residuals using the Kolmogorov-Smirnov and Layard tests, respectively. The data was then subjected to analysis of variance using the F-test at p ≤ 0.01. Variables with significant differences (p-value ≤ 0.01) were subjected to regression analysis. The models were selected based on the significance of the equation (t-test, p-value ≤ 0.01), the coefficient of determination (R2), and knowledge of the evolution of the biological phenomenon. The statistical analyses were performed using the R® software.

Results and Discussion

After pre-drying, the moisture content of S. aethiopicum (cultivar Tinguá-verde-claro) seeds was approximately 29% (Figure 1). The drying time required to reduce the moisture content to approximately 7% was 0.75, 0.66, 0.50, and 0.33 hours (45, 40, 30, and 20 min) at 35, 38, 41, and 44 ºC, respectively. It can be seen that the drying time of S. aethiopicum seeds decreases with increasing air temperature due to the increase in the pressure gradient between the inside of the seed and the surrounding air. Similar results were found for pepper seeds (Capsicum spp) (Reis et al., 2015Reis, D. R. D.; Santos, P. D.; Silva, F. S. D.; Porto, A. G. Influência das características do ar na cinética de secagem de pimenta variedade bico. Brazilian Journal of Food Technology, v.18, p.146-154, 2015. https://doi.org/10.1590/1981-6723.6214
https://doi.org/10.1590/1981-6723.6214...
; Silva et al., 2018Silva, H. W. D.; Vale, L. S.; Silva, C. F.; Souza, R. D. C. Drying kinetics and physiological quality of ‘Cabacinha’ pepper seeds during storage. Revista Brasileira de Engenharia Agrícola e Ambiental , v.22, p.292-297, 2018. https://doi.org/10.1590/1807-1929/agriambi.v22n4p292-297
https://doi.org/10.1590/1807-1929/agriam...
).

Figure 1
Moisture content during drying of S. aethiopicum (cultivar Tinguá-verde-claro) seeds at different temperatures

It is important, furthermore, to highlight that reducing drying time is crucial to preserving seed quality. The faster the seeds are dried, the shorter the exposure time to unfavorable conditions, such as the proliferation of microorganisms and the risk of fermentation. However, it is important to emphasize that high temperatures of the drying air can compromise the physiological quality of the seeds, as they may cause damage to membrane systems and protein denaturation (Rosa et al., 2023Rosa, C. O.; Silva, F. A.; Cruz, D. R. C.; Santos, S. G. F. Importância da secagem e armazenamento adequados na manutenção da qualidade de sementes de pimenta (Capsicum). Research, Society and Development, v.12, p.1-14, 2023. http://dx.doi.org/10.33448/rsd-v12i8.43000
http://dx.doi.org/10.33448/rsd-v12i8.430...
).

Table 2 shows the models used to predict the drying process of S. aethiopicum seeds. Among the various models, Logarithm, Midilli, and Modified Midilli showed a coefficient of determination (R2) higher than 0.993 for all temperatures, which was not the case for the other models studied. According to Karizaki (2016Karizaki, I. V. M. Kinetic modeling and determination of mass transfer parameters during cooking of rice. Innovative Food Science and Emerging Technologies, v.38, p.131-138, 2016. https://doi.org/10.1016/j.ifset.2016.09.017
https://doi.org/10.1016/j.ifset.2016.09....
), higher R2 values indicate that the model had a better fit to the experimental data. However, it is worth highlighting that using this parameter alone is insufficient for the selection of non-linear models (Corrêa Filho et al., 2015Corrêa Filho, L. C.; Andrade, E. T. D.; Martinazzo, A. P.; Andrea, E. M.; Sousa, F. A. D.; Figueira, V. G. Cinética de secagem, contração volumétrica e análise da difusão líquida do figo (Ficus carica L.). Revista Brasileira de Engenharia Agrícola e Ambiental, v.19, p.797-802, 2015. https://doi.org/10.1590/1807-1929/agriambi.v19n8p797-802
https://doi.org/10.1590/1807-1929/agriam...
). For this reason, the relative mean error (P), the estimated mean error (SE), and the chi-squared test (χ2) were considered.

Table 2
Coefficients of determination (R2), relative mean error (P, %), estimated mean error (SE, decimal), and chi-squared test (χ2, decimal) for the models fitted to the experimental data for drying S. aethiopicum (cultivar Tinguá-verde-claro) seeds

For a model to adequately represent any phenomenon, it must have a relative mean error lower than 10% (Piekutowska et al., 2021Piekutowska, M.; Niedbała, G.; Piskier, T.; Lenartowicz, T.; Pilarski, K.; Wojciechowski, T.; Czechowska-Kosacka, A. The application of multiple linear regression and artificial neural network models for yield prediction of very early potato cultivars before harvest. Agronomy, v.11, e885, 2021.https://doi.org/10.3390/agronomy11050885
https://doi.org/10.3390/agronomy11050885...
), a chi-squared test, and an estimated mean error as close to zero as possible (Silva et al., 2022Silva, F. B.; Santos, S. G. F.; Almeida, V. G.; Rezende, G.; Xavier, I. R. R. Cinética de secagem e qualidade fisiológica de sementes de milho. Revista de Ciências Agrárias , v.45, p.24-33, 2022. https://doi.org/10.19084/rca.27094
https://doi.org/10.19084/rca.27094...
). As a result, the Logarithm, Midilli, and Modified Midilli models exhibited low standard error (SE) and χ2 values, with P-values below 10%, regardless of the temperature studied, and are recommended for representing the drying of S. aethiopicum seeds (Table 2). However, the Bayesian Information Criterion (BIC) and the Akaike Information Criterion (AIC) were utilized to select a single model.

The values obtained for BIC and AIC for the Logarithm, Midilli, and Modified Midilli models are described in Table 3. Lower values for these criteria indicate a better fit of the model to the drying data (Ferreira Júnior et al., 2020Ferreira Junior, W. N.; Resende, O.; Pinheiro, G. K.; Silva, L. C. M.; Costa, E. R. Use of AIC and BIC in desorption isotherms of tamarind seeds (Tamarindus indica L.). Engenharia Agrícola, v.40, p.511-517, 2020. http://dx.doi.org/10.1590/1809-4430-Eng.Agric.v40n4p511-517/2020
http://dx.doi.org/10.1590/1809-4430-Eng....
). Therefore, it is observed that the Modified Midilli model showed lower AIC and BIC values, thus being chosen to represent the drying of S. aethiopicum seeds. The regression coefficients of the Modified Midilli model adjusted for temperatures of 35, 38, 41, and 44 ºC are shown in Eqs. 17, 18, 19, and 20, respectively.

R X 35 = e x p - 1 . 1879 * * t 0 . 7779 * * + - 0 . 4766 * * t (17)

R X 38 = e x p - 0 . 6773 * * t 0 . 7213 * * + - 0 . 8101 * * t (18)

R X 41 = e x p - 0 . 8988 * * t 0 . 7775 * * + - 1 . 047 * * t (19)

R X 44 = e x p - 6 . 2704 * * t 1 . 1410 * * + - 0 . 0943 * * t (20)

** - Significant at p ≤ 0.01 by t-test.

Table 3
Akaike Information Criterion (AIC) and Schwartz Bayesian Information Criterion (BIC) values for the Logarithm, Midilli, and Modified Midilli models adjusted to the drying curves of S. aethiopicum (cultivar Tinguá-verde-claro) seeds at different temperatures

Figure 2 shows the drying curves of S. aethiopicum seeds at temperatures of 35, 38, 41, and 44 ºC, with the values estimated by the Modified Midilli model. It should be noted that the Modified Midilli model has been used to represent the drying of various agricultural products such as Aztec amaranth seeds (Costa et al., 2021Costa, P. M.; Bianchini, A.; Caneppele, C.; Azevedo, P. H. D.; Silva, A. L. D. Drying kinetics of Amaranthus cruentus ‘BRS Alegria’ seeds in natural and artificial methods. Revista Brasileira de Engenharia Agrícola e Ambiental , v.25, p.345-352, 2021. https://doi.org/10.1590/1807-1929/agriambi.v25n5p345-352
https://doi.org/10.1590/1807-1929/agriam...
), corn seeds (Silva et al., 2022Silva, F. B.; Santos, S. G. F.; Almeida, V. G.; Rezende, G.; Xavier, I. R. R. Cinética de secagem e qualidade fisiológica de sementes de milho. Revista de Ciências Agrárias , v.45, p.24-33, 2022. https://doi.org/10.19084/rca.27094
https://doi.org/10.19084/rca.27094...
), and jackfruit almond (Santos et al., 2021Santos, D. F. A. L.; Rocha, A. A.; Santos, G. A. S.; Paixão, L. C.; Santana, A. A. Amêndoa de jaca: caracterização físico-química, tratamento osmótico, cinética de secagem e modelagem matemática. Brazilian Journal of Development , v.7, p.11194-11210, 2021. https://doi.org/10.34117/bjdv7n1-765
https://doi.org/10.34117/bjdv7n1-765...
).

Figure 2
Experimental values and values estimated by the Modified Midilli model for moisture ratio (RX) according to the drying time of S. aethiopicum (cultivar Tinguá-verde-claro) seeds

Table 4 shows the analysis of variance for the variables relating to the physiological quality of the S. aethiopicum (Tinguá-verde-claro) seeds, which were subjected to different drying temperatures. It can be seen that the first germination count, electrical conductivity, and accelerated aging were significantly influenced by the treatments (p ≤ 0.01). The germination, on the other hand, was not influenced (p > 0.01).

Table 4
Summary of the analysis of variance for the first germination count (FGG), germination (G), electrical conductivity (EC), and accelerated aging (AA) of S. aethiopicum (Tinguá-verde-claro) seeds subjected to different drying temperatures

The different drying temperatures did not influence germination, with a mean value of 92.93% (Figure 3B). However, for the first germination count, the detrimental effect of the drying temperature of 44 ºC on the seeds is noticeable, with an average of 58.0% of normal seedlings (Figure 3A). On the other hand, the drying temperature of 38 ºC produced superior results, with an average of 84.0%, followed by 41 and 35 ºC, with averages of 75.5 and 70.5%, respectively. It is important to emphasize that the first germination count is a vigor test, based on the germination speed, where more vigorous seeds germinate more quickly and take better advantage of the environmental conditions (Guedes et al., 2015Guedes, R. S.; Alves, E. U.; Santos-Moura, S. S.; Galindo, E. A. Teste de comprimento de plântula na avaliação da qualidade fisiológica de sementes de Amburana cearensis (Allemão) A.C. Smith. Semina: Ciências Agrárias, v.36, p.2373-2382, 2015. https://doi.org/10.5433/1679-0359.2015v36n4p2373
https://doi.org/10.5433/1679-0359.2015v3...
). Therefore, although no difference was observed between treatments in the final germination count, it is evident that drying at 44 ºC impairs seed vigor, resulting in slower germination compared to other temperatures.

Figure 3
First germination count (A) and germination (B) of ‘Tinguá-verde-claro’ S. aethiopicum seeds as a function of drying temperature

The increase in temperature resulted in a higher electrical conductivity of the solution (Figure 4). Higher electrical conductivity values are associated with a greater release of exudates into the external environment through the cell membrane, indicating that the seeds are more deteriorated and less vigorous (Haesbaert et al., 2017Haesbaert, F. M.; Lopes, S. J.; Mertz, L. M.; Lúcio, A. D. C.; Huth, C. Tamanho de amostra para determinação da condutividade elétrica individual de sementes de girassol.Bragantia, v.76, p.54-61, 2017. https://doi.org/10.1590/1678-4499.389
https://doi.org/10.1590/1678-4499.389...
). Therefore, it can be observed that drying at 44 ºC had a detrimental effect on the quality of S. aethiopicum seeds. This may be associated with the oxidation of cell membranes resulting from the production of free radicals induced by exposure to high temperatures. On the other hand, low electrical conductivity was observed during the drying process at lower temperatures (35 and 38 ºC). It is relevant to highlight that slow drying enables a gradual reduction in moisture content and, consequently, the functioning of desiccation tolerance mechanisms, allowing for the obtainment of more vigorous seed lots (Marcos Filho, 2015Marcos Filho, J. Fisiologia de sementes de plantas cultivadas. 1.ed. Londrina: Abrates, 2015. 660p.).

Figure 4
Electrical conductivity of S. aethiopicum (Tinguá-verde-claro) seeds according to the drying temperature

The percentages of normal seedlings for each drying temperature after the accelerated aging test are shown in Figure 5. It can be seen that the increase in temperature led to a reduction in germination, especially at temperatures of 41 and 44 ºC, with averages of 76.5 and 71.5%, respectively. On the other hand, drying the seeds at 35 and 38 ºC obtained better results (averages of 87 and 79.5%, respectively), corroborating the electrical conductivity test (Figure 4). It is known that the accelerated aging test was introduced to evaluate the storage potential of seeds (Marcos Filho, 2015Marcos Filho, J. Fisiologia de sementes de plantas cultivadas. 1.ed. Londrina: Abrates, 2015. 660p.), and it is, therefore, an excellent method for differentiating seed lots with varying levels of vigor.

Figure 5
Percentage of normal seedlings after accelerated aging of S. aethiopicum (cultivar ‘Tinguá-verde-claro) seeds according to the drying temperature

In general, drying vegetable seeds at 35 and 38 ºC has produced seed lots with improved physiological quality. Similar outcomes were observed in ‘dedo de moça’ pepper seeds by Silva et al. (2018Silva, H. W. D.; Vale, L. S.; Silva, C. F.; Souza, R. D. C. Drying kinetics and physiological quality of ‘Cabacinha’ pepper seeds during storage. Revista Brasileira de Engenharia Agrícola e Ambiental , v.22, p.292-297, 2018. https://doi.org/10.1590/1807-1929/agriambi.v22n4p292-297
https://doi.org/10.1590/1807-1929/agriam...
), where drying at these temperatures ensured the obtention of high-vigor seeds. These results have also been observed in eggplant seeds (Weber et al., 2013Weber, L. C.; Amaral-Lopes, A. C.; Boiteux, L. S.; Nascimento, W. M. Produção e qualidade de sementes híbridas de berinjela em função do número de frutos mantidos por planta após polinização controlada. Horticultura Brasileira, v.31, p.461-466, 2013. https://doi.org/10.1590/S0102-05362013000300019
https://doi.org/10.1590/S0102-0536201300...
; Zamariola et al., 2014Zamariola, N.; Oliveira, J. A.; Gomes, L. A. A.; Jácome, M. F.; Reis, L.V. Effect of drying, pelliculation and storage on the physiological quality of eggplant seeds. Journal of Seed Science, v.36, p.240-245, 2014. https://doi.org/10.1590/2317-1545v32n2959
https://doi.org/10.1590/2317-1545v32n295...
; Çelik & Kenanoğlu, 2023Çelik, Y.; Kenanoğlu, B. B. After-ripening effect combined with drying methods on seed quality of aubergine seed lots harvested at different maturity stages. Kuwait Journal of Science, v.50, p.353-358, 2023. https://doi.org/10.1016/j.kjs.2023.05.013
https://doi.org/10.1016/j.kjs.2023.05.01...
).

Ultimately, it is crucial to conduct additional research exploring different drying methods in vegetables, such as intermittent drying, and to investigate the effects of this process during seed storage, especially concerning S. aethiopicum, where there is a notable lack of information on the production and technology of its seeds in the literature.

Conclusions

  1. The drying process of S. aethiopicum (Tinguá-verde-clara) seeds at temperatures of 35, 38, 41, and 44 ºC is represented the best by the Modified Midilli model.

  2. Drying S. aethiopicum seeds at 35 and 38 ºC resulted in better physiological quality.

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  • 1 Research developed at Universidade Federal de Viçosa, Departamento de Agronomia, Viçosa, MG, Brazil

Financing statement

  • There are no financing statements to declare.
  • Supplementary documents

    There are no supplementary sources.

Edited by

Editors: Geovani Soares de Lima & Carlos Alberto Vieira de Azevedo

Data availability

There are no supplementary sources.

Publication Dates

  • Publication in this collection
    12 Aug 2024
  • Date of issue
    Nov 2024

History

  • Received
    05 Jan 2024
  • Accepted
    09 June 2024
  • Published
    29 June 2024
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