Abstract:

Seedlings for commercial growing of passion fruit are preferentially acquired through seeds. Success in germination and seedling emergence, in turn, is influenced by the genetic constitution of the progenies and the thermal conditions imposed on the growth environment. The aim of this study was to evaluate the emergence and vigor of seedlings of passion fruit cultivars exposed to different temperatures. The experiment was conducted in a germination chamber at the Unidade de Ensino, Pesquisa e Extensão / Pomar Campus of the Department of Plant Science of the Universidade Federal de Viçosa (UFV). The study was carried out in 5 × 3 factorial arrangement, with five temperature ranges (5-15, 10-20, 15-25, 20-30 and 25-35 °C) and three varieties of passion fruit (BRS Sol do Cerrado, BRS Gigante Amarelo and FB-200 Yellow Master) in a completely randomized design with six replications of 25 seeds per plot. The variables analyzed were the percentage, the speed index, and the average time of emergence, shoot length, total length, and seedling dry matter. The cultivars BRS Sol do Cerrado and BRS Gigante Amarelo exhibited seedling emergence of over 95% in the temperature ranges of 20-30 °C and 25-35 °C. Alternating temperatures from 20-30 °C stimulates seedling emergence, seedling growth, and greater accumulation of seedling dry matter.

Index terms:
Passiflora edulis Sims; cultivars; seeds; thermal conditions

Resumo:

A propagação de plantas de maracujazeiro azedo, em plantios comerciais, é realizada preferencialmente por meio de sementes. O sucesso da germinação e emergência de plântulas, por sua vez, é influenciado pela constituição genéticas das progênies e pelas condições térmicas impostas no ambiente. O objetivo neste trabalho foi avaliar a emergência e o vigor de plântulas de cultivares de maracujazeiro azedo sob exposição de diferentes temperaturas. O experimento foi conduzido em câmara de germinação na Unidade de Ensino, Pesquisa e Extensão/Pomar Campus pertencente ao Departamento de Fitotecnia da UFV. O trabalho foi desenvolvido em esquema fatorial 5 × 3, com cinco faixas de temperatura (5-15; 10-20; 15-25; 20-30 e 25-35 °C) e três cultivares de maracujazeiro azedo (BRS Sol do Cerrado, BRS Gigante Amarelo e FB-200 Yellow Master) no delineamento inteiramente casualizado e seis repetições de 25 sementes por parcela. As variáveis analisadas foram as percentagem, índice de velocidade e tempo médio de emergência, o comprimento da parte aérea e total e massa seca de plântula. As cultivares BRS Sol do Cerrado e BRS Gigante Amarelo apresentaram emergência de plântulas acima de 95% nas faixas de temperaturas de 20-30 °C e 25-35 °C. Temperaturas alternadas 20-30 °C estimulam a emergência, o crescimento e maior acúmulo de massa seca das plântulas.

Termos de indexação:
Passiflora edulis Sims; cultivares; sementes; condições térmicas

Introduction

The passion fruit plant (Passiflora edulis Sims), also known as yellow passion fruit (maracujazeiro amarelo), belongs to the Passifloraceae family, which includes 12 genera and around 600 species distributed across the tropical zones of America and Africa (Bernacci et al., 2008BERNACCI, L.C.; SOARES-SCOTT, M.D.; JUNQUEIRA, N.T.V.; PASSOS, I.R.S.; MELETTI, L. M. M. Passiflora edulis SIMS: the correct taxonomic way to cite the yellow passion fruit (and of others colors). Revista Brasileira de Fruticultura , v.30, n.2, p.566-576, 2008. http://dx.doi.org/10.1590/S0100-29452008000200053
http://dx.doi.org/10.1590/S0100-29452008... ). In the industrial agriculture network, this species represents around 95% of commercial production of passion fruit, due to its excellent vigor, fruit yield, and juice content (Costa et al., 2011COSTA, E.; SANTOS, L.A.R.; CARVALHO, C.; LEAL, P.A.M.; GOMES, V.A. Volumes de substratos comerciais, solo e composto orgânico afetando a formação de mudas de maracujazeiro-amarelo em diferentes ambientes de cultivo. Revista Ceres, v.58, n.2, p.216-222, 2011. http://dx.doi.org/10.1590/S0034-737X2011000200013
http://dx.doi.org/10.1590/S0034-737X2011... ; Melleti, 2011MELLETI, L.M.M. Avanço na cultura do maracujazeiro no Brasil. Revista Brasileira de Fruticultura , v.33, n.1, p. 83-91, 2011. http://dx.doi.org/10.1590/S0100-29452011000500012
http://dx.doi.org/10.1590/S0100-29452011... ).

Plant propagation of passion fruit in commercial fields is preferentially through seeds, seminiferous (Silva et al., 2015SILVA, M.S.; OLIVEIRA, R.C.; ALMEIDA, R.F.; SÁ JUNIOR, A.; SANTOS, C.M. Aryl removal methods and passion fruit seed positions: Germination and emergence. Journal of Seed Science, v.37, n.2, p. 125-130, 2015. http://dx.doi.org/10.1590/2317-1545v37n2146373
http://dx.doi.org/10.1590/2317-1545v37n2... ), but lack of uniformity of germination and seedling emergence is reported by producers and nurseries, which creates difficulties in raising quality seedlings and establishing productive orchards. This lack of uniformity is related to the dormancy process present in various species of Passifloraceae, as reported by Osipi and Nakagawa (2005OSIPI, E.A.F.; NAKAGAWA, J. Temperatura na avaliação da qualidade fisiológica de sementes do maracujá-doce (Passiflora alata Dryander). Revista Brasileira de Fruticultura , v.27, n.1, p. 179-191, 2005. http://dx.doi.org/10.1590/S0100-29452005000100048
http://dx.doi.org/10.1590/S0100-29452005... ) in Passiflora alata Dryander, by Zucareli et al. (2009ZUCARELI, V.; FERREIRA, G.; AMARO, A.C.E.; ARAÚJO, F.P. Fotoperíodo, temperatura e reguladores vegetais na germinação de sementes de Passiflora cincinnata Mast. Revista Brasileira de Sementes , v. 31, n.3, p. 106-114, 2009. http://dx.doi.org/10.1590/S0101-31222009000300012
http://dx.doi.org/10.1590/S0101-31222009... ) in Passiflora cincinnata Mast., and Zucareli et al. (2015)ZUCARELI, V.; HENRIQUE, L.A.; ONO, E.O. Influence of light and temperature on the germination of Passiflora incarnata L. seeds. Journal of Seed Science , v.34, n.2, p.162-167, 2015. http://dx.doi.org/10.1590/2317-1545v37n2147082
http://dx.doi.org/10.1590/2317-1545v37n2... in Passiflora incarnata L.

Germination and, consequently, seedling emergence is a process of resuming metabolic activity of the embryonic axis, culminating in radicle emergence. It is a critical phase, associated with factors related to the physical, biochemical, and physiological processes of the seed (Marini et al., 2012MARINI, P.; MORAES, C.L.; MARINI, N.; MORAES, D.M.; AMARANTE, L. Alterações fisiológicas e bioquímicas em sementes de arroz submetidas ao estresse térmico. Revista Ciência Agronômica, v. 43, n. 4, p. 722-730, 2012. http://dx.doi.org/10.1590/S1806-66902012000400014
http://dx.doi.org/10.1590/S1806-66902012... ; Taiz and Zeiger, 2013TAIZ, L.; ZEIGER, E. Fisiologia vegetal. Porto Alegre: Artmed , 2013. 954p.), which are dependent on environmental conditions such as temperature (Bewley et al., 2014BEWLEY, J.D.; BRADFORD, K.J.; HILHORST, H.W.M.; NONOGAKI, H. Seeds: physiology of development, germination and dormancy. New York: Springer, 2014. 407p.; Zucareli et al., 2015ZUCARELI, V.; HENRIQUE, L.A.; ONO, E.O. Influence of light and temperature on the germination of Passiflora incarnata L. seeds. Journal of Seed Science , v.34, n.2, p.162-167, 2015. http://dx.doi.org/10.1590/2317-1545v37n2147082
http://dx.doi.org/10.1590/2317-1545v37n2... ).

Studies related to the effect of air temperature on germination of the passion fruit plant are essential for understanding ecophysiological and biochemical processes and how the seeds are influenced by the thermal conditions provided by the environment (Ferreira and Borghetti, 2004FERREIRA, A.G., BORGHETTI, F. Germinação: do básico ao aplicado. Porto Alegre: Artmed, 2004. 323 p.). There are minimum and maximum temperatures that represent the lower and upper limit of germination, and optimum temperatures under which the germination process occurs more quickly in a shorter space of time (Marcos-Filho, 2005MARCOS-FILHO, J. Fisiologia de sementes de plantas cultivadas. Piracicaba: FEALQ, 2005. 495p.).

The temperature affects moisture uptake and regulates the biochemical and enzymatic reactions that regulate metabolism, reactions that are involved in the germination process (Bewley et al., 2014BEWLEY, J.D.; BRADFORD, K.J.; HILHORST, H.W.M.; NONOGAKI, H. Seeds: physiology of development, germination and dormancy. New York: Springer, 2014. 407p.; Flores et al., 2014FLORES, A.V.; BORGES, E.E.L.; GUIMARÃES, V.M.; GONÇALVES, J.F.C.; ATAÍDE, C. M.; BARROS, D. P. Atividade enzimática durante a germinação de sementes de Melanoxylon brauna Schott sob diferentes temperaturas. Cerne, v.20, n.2, p.401-408, 2014. http://dx.doi.org/10.1590/01047760201420031399
http://dx.doi.org/10.1590/01047760201420... ). Germination is variable, depending on the species and even within cultivars of the same species (Andrade and Jasper, 2013ANDRADE, R.A.; JASPER, S.P. Temperatura na emergência de quatro variedades de mamoeiro. Comunicata Scientiae, v.4, n.4, p.401-406, 2013. https://comunicatascientiae.com.br/comunicata/article/view/272/211
https://comunicatascientiae.com.br/comun... ; Lone et al., 2014LONE, A.B.; COLOMBO, R.C.; FAVETTA, V.; TAKAHASHI, L.S.A.; FARIA, R.T. Temperatura na germinação de sementes de genótipos de pitaya. Semina: Ciências Agrárias, v.35, n.4, p.2251-2258, 2014. http://dx.doi.org/10.5433/1679-0359.2014v35n4Suplp2251
http://dx.doi.org/10.5433/1679-0359.2014... ); each species requires an optimal range of temperature for this process to occur in the most efficient manner.

Considering that the germination response of fruit-bearing species is dependent not only on air temperature conditions, but also on the genetic constitution of the progenies used, and that this information still needs to be clarified for the passion fruit crop, the aim of this study was to evaluate the effect of exposure to different temperature ranges on the emergence and seedling vigor of passion fruit cultivars.

Materials and Methods

The experiment was conducted in a germination chamber with control of photoperiod and temperature conditions at the Department of Plant Science of the University Federal of Viçosa, Viçosa, Minas Gerais, Brazil, in the period of January to February 2016.

The study was conducted in a 5 × 3 factorial arrangement (5 temperature ranges and 3 commercial cultivars of passion fruit) in a completely randomized design with six replications per treatment and 25 seeds per experimental unit. The ranges of alternating temperatures used were 5-15 °C, 10-20 °C, 15-25 °C, 20-30 °C and 25-35 °C, and the passion fruit cultivars used were BRS Sol do Cerrado, BRS Gigante Amarelo, and FB-200 Yellow Master. Seeds of the passion fruit cultivars used were acquired from the Viveiros Flora Brasil, Araguari, Minas Gerais, Brazil.

The photoperiod was 8 h, with lights on during the day and 16 h of lights out at night. The lower temperature was established under the conditions of absence of photoperiod and the higher temperature established under the condition of photoperiod. The passion fruit seeds were selected and standardized in regard to size and weight and sown in inert substrate (washed sand) at 2 cm depth and a 4 cm spacing between rows. The substrate was irrigated every 24 h, maintaining moisture sufficient for favoring germination and seedling emergence.

Before the experiment was set up, an imbibition test of the passion fruit seeds was carried out at the respective mean temperatures used in the experiment so as to verify the speed and amount of water uptake. To do so, at each mean temperature of the ranges tested (namely, 10, 15, 20, 25 and 30 °C), 4 samples of 10 seeds of each cultivar were immersed in a beaker containing 50 mL of distilled water, and the amount of water taken up in periods of evaluation of 12, 24, 48 and 72 h after imbibition was evaluated. The amount of water imbibed in each period was measured through the difference between the final weight in each period of evaluation and the initial weight of the samples before imbibition, considering water density equal to 1, which was expressed in milliliters (mL).

The number of emerged seedlings was counted daily from the 7th to the 28th day after sowing (DAS) to verify stabilization of germination, according to the methodology contained in the Rules for Seed Testing for the passion fruit seeds (Brasil, 2009BRASIL. Ministério da Agricultura, Pecuária e Abastecimento. Regras para análise de sementes. Ministério da Agricultura, Pecuária e Abastecimento. Secretaria de Defesa Agropecuária. Brasília, DF: MAPA/ACS, 2009. 395p. http://www.agricultura.gov.br/arq_editor/file/2946_regras_analise__sementes.pdf
http://www.agricultura.gov.br/arq_editor... ). Emerged seedlings were considered to be those that had cotyledons fully expanded above the surface of the substrate. Following the methodology of Ferreira and Borghetti (2004FERREIRA, A.G., BORGHETTI, F. Germinação: do básico ao aplicado. Porto Alegre: Artmed, 2004. 323 p.), the percentage of emergence at 7, 14, 21, 28 DAS, the mean emergence time (MET) (Eq. 1) and the emergence speed index (ESI) (Eq. 2) were evaluated.

MET = (∑niti / ∑ni) Eq. 1

in which ni = number of seeds that germinated in time “i”; ti = time after setting up the test; i = 1 to 28 days.

ESI = E1/N1 + E2/N2 + ... + En/Nn Eq. 2

in which E1, E2, ..., En = number of normal seedlings counted in the first, second, and last count; N1, N2, Nn = number of days of sowing to the first, second, and last count.

At the end of the experiment, shoot length (SL) and total length (TL) were evaluated with a ruler in millimeters. Soon after biometric measurements, the seedlings were placed in paper bags and then in a forced air circulation oven at a temperature of 65 °C for a period of 48 h until reaching constant weight to obtain individual dry matter (IDM) of the seedling, measured on a semi-analytic balance.

The values of emergence percentage were transformed into arcsin (x/100)^0.5; however, the data presented in the tables and figures refer to the original data, for better understanding. The data obtained were subjected to analysis of variance by the F test at 5% probability. The mean values in regard to the temperature ranges and the cultivars of passion fruit plants and the interaction between them were compared by the Tukey test at 5% probability. The GENES statistical software (Cruz, 2013CRUZ, C.D. GENES - a software package for analysis in experimental statistics and quantitative genetics. Acta Scientiarum. Agronomy, v.35, n.3, p.271-276, 2013. http://dx.doi.org/10.4025/actasciagron.v35i3.21251
http://dx.doi.org/10.4025/actasciagron.v... ) was used for data analysis.

Results and Discussion

The evolution of imbibition of the seeds of the passion fruit cultivars as affected by temperature and period are shown in Figure 1. The biggest volume of water imbibed by the passion fruit seeds was observed at the mean temperature of 30 °C, with peak water uptake in the period of 72 h after imbibition for the cultivar BRS Sol do Cerrado, 24 h for BRS Gigante Amarelo, and 48 h for FB-200 Yellow Master (Figures 1A, B, and C). At the mean temperature of 10 °C, lower water uptake of the seed of the passion fruit cultivars was observed, with the cultivar BRS Sol do Cerrado standing out. The mean temperatures of 15, 20 and 25 °C showed a similar response in relation to water uptake by the seeds.

Marcos-Filho (2005)MARCOS-FILHO, J. Fisiologia de sementes de plantas cultivadas. Piracicaba: FEALQ, 2005. 495p. affirms that it is important to characterize the seed imbibition process because higher temperatures contribute to greater activation of the energy of water, increasing introduction of water into the seeds in a shorter space of time, favoring reactivation of the germination processes, with an increase in respiratory activity and release of energy for germination.

In the ‘Mariana’ hybrid tomato plant, Ferreira et al. (2013FERREIRA, R.L.; FORTI, V.A.; SILVA, V.N.; MELO, S.C. Temperatura inicial de germinação no desempenho de plântulas e mudas de tomate. Ciência Rural, v.43, n.7, p.1189-1195, 2013. http://dx.doi.org/10.1590/S0103-84782013000700008
http://dx.doi.org/10.1590/S0103-84782013... ) found that temperatures higher than 30 ºC led to greater water uptake by seeds in comparison to the control treatment (20-30 °C), and uptake was faster in the first 25 h, determining this period as the first phase of germination. After this period, stabilization of seed moisture content was observed, characterizing it as phase II of germination. This phase is recognized by drastic reduction in the speed of seed hydration (Marcos-Filho, 2005MARCOS-FILHO, J. Fisiologia de sementes de plantas cultivadas. Piracicaba: FEALQ, 2005. 495p.; Nonogaki et al., 2010NONOGAKI, H.; BASSEL, G.W.; BEWLEY, J.D. Germination - still a mystery. Plant Science, v.179, n. 6, p. 574-581, 2010. http://dx.doi.org/10.1016/j.plantsci.2010.02.010
http://dx.doi.org/10.1016/j.plantsci.201... ).

When seeds were kept at temperatures of 5-15 °C and 10-20 °C, there was no emergence of seedlings of the passion fruit cultivars in 28 DAS evaluated (Figures 2A, B, and C). At temperatures above these, emergence began at 13, 9 and 7 DAS in the temperature ranges of 15-25 °C, 20-30 °C and 25-35 °C, and there was stability of emergence at 24, 20 and 16 DAS, respectively.

The effect of temperature on germination of fruit-bearing plants has been widely studied in recent years, and it is possible to know the characteristics of each species in regard to ability for seedling propagation in determined locations and times of the year, which may also vary depending on the genetic, physiological, and physical quality and state of health of the seed (Andrade and Jasper, 2013ANDRADE, R.A.; JASPER, S.P. Temperatura na emergência de quatro variedades de mamoeiro. Comunicata Scientiae, v.4, n.4, p.401-406, 2013. https://comunicatascientiae.com.br/comunicata/article/view/272/211
https://comunicatascientiae.com.br/comun... ); each species requires a determined range of temperature and an optimum temperature at which the germination process occurs with greater speed and uniformity (Alves et al., 2012ALVES, E. U.; SANTOS-MOURA, S.S.; MOURA, M. F.; GUEDES, R. S.; ESTRELA, F.A. Germinação e vigor de sementes de Crataeva tapia L. em diferentes substratos e temperaturas. Revista Brasileira de Fruticultura, v.34, n.4, p.1208-1215, 2012. http://dx.doi.org/10.1590/S0100-29452012000400030
http://dx.doi.org/10.1590/S0100-29452012... ).

From the results, it can be seen that the higher temperatures (20-30 °C and 25-35 °C) stimulate early development, a greater peak of emergence, and rapid stability of emergence. BRS Sol do Cerrado (Figure 2A) and BRS Gigante Amarelo (Figure 2B) were the cultivars that exhibited near totality of emerged seedlings. There is a differentiated response in regard to the requirement for a thermal range, and this is variable depending on the genetic material, as reported by Andrade and Jasper (2013ANDRADE, R.A.; JASPER, S.P. Temperatura na emergência de quatro variedades de mamoeiro. Comunicata Scientiae, v.4, n.4, p.401-406, 2013. https://comunicatascientiae.com.br/comunicata/article/view/272/211
https://comunicatascientiae.com.br/comun... ) for varieties of papaya plant and Lone et al. (2014LONE, A.B.; COLOMBO, R.C.; FAVETTA, V.; TAKAHASHI, L.S.A.; FARIA, R.T. Temperatura na germinação de sementes de genótipos de pitaya. Semina: Ciências Agrárias, v.35, n.4, p.2251-2258, 2014. http://dx.doi.org/10.5433/1679-0359.2014v35n4Suplp2251
http://dx.doi.org/10.5433/1679-0359.2014... ) for pitaya genotypes.

The emergence percentage evaluated in the periods of 7, 14, 21 and 28 DAS was affected by the temperature ranges and the cultivars used, with high mean values of emergence at the temperatures of 20-30 °C and 25-35 °C and inhibition of emergence at the temperatures of 5-15 °C and 10-20 °C (Table 1). In evaluation performed at 7 DAS, only the cultivars BRS Sol do Cerrado and FB-200 Yellow Master emerged when subjected to temperature alternating from 25-35 °C; however, at 14 DAS, the cultivars BRS Sol do Cerrado and BRS Gigante Amarelo already exhibited more than 93% emergence at this temperature, indicating that high temperatures contribute to early germination and seedling emergence of passion fruit plants.

Exposure to low temperatures over a prolonged period can induce seed dormancy in species of the Passifloraceae family (Osipi and Nakagawa, 2005OSIPI, E.A.F.; NAKAGAWA, J. Temperatura na avaliação da qualidade fisiológica de sementes do maracujá-doce (Passiflora alata Dryander). Revista Brasileira de Fruticultura , v.27, n.1, p. 179-191, 2005. http://dx.doi.org/10.1590/S0100-29452005000100048
http://dx.doi.org/10.1590/S0100-29452005... ; Zucareli et al., 2009ZUCARELI, V.; FERREIRA, G.; AMARO, A.C.E.; ARAÚJO, F.P. Fotoperíodo, temperatura e reguladores vegetais na germinação de sementes de Passiflora cincinnata Mast. Revista Brasileira de Sementes , v. 31, n.3, p. 106-114, 2009. http://dx.doi.org/10.1590/S0101-31222009000300012
http://dx.doi.org/10.1590/S0101-31222009... ; Zucareli et al., 2015ZUCARELI, V.; HENRIQUE, L.A.; ONO, E.O. Influence of light and temperature on the germination of Passiflora incarnata L. seeds. Journal of Seed Science , v.34, n.2, p.162-167, 2015. http://dx.doi.org/10.1590/2317-1545v37n2147082
http://dx.doi.org/10.1590/2317-1545v37n2... ), reduced by the lower speed of water imbibition (Figure 1), without softening of the seed coat and, consequently, lack of protrusion of the radicle (Marini et al., 2012MARINI, P.; MORAES, C.L.; MARINI, N.; MORAES, D.M.; AMARANTE, L. Alterações fisiológicas e bioquímicas em sementes de arroz submetidas ao estresse térmico. Revista Ciência Agronômica, v. 43, n. 4, p. 722-730, 2012. http://dx.doi.org/10.1590/S1806-66902012000400014
http://dx.doi.org/10.1590/S1806-66902012... ). In addition, it reduces the activity of enzymes related to the germination process - lipase, amylase, and protease - and increases the activity of enzymes related to stress - superoxide dismutase and catalase (Marcos-Filho, 2005MARCOS-FILHO, J. Fisiologia de sementes de plantas cultivadas. Piracicaba: FEALQ, 2005. 495p.; Flores et al., 2014FLORES, A.V.; BORGES, E.E.L.; GUIMARÃES, V.M.; GONÇALVES, J.F.C.; ATAÍDE, C. M.; BARROS, D. P. Atividade enzimática durante a germinação de sementes de Melanoxylon brauna Schott sob diferentes temperaturas. Cerne, v.20, n.2, p.401-408, 2014. http://dx.doi.org/10.1590/01047760201420031399
http://dx.doi.org/10.1590/01047760201420... ). While at a higher temperature up to a certain point, it contributes to accelerating the speed of water uptake and also to reactions that determine all the biochemical and enzymatic processes involved in germination (Marcos-Filho, 2005MARCOS-FILHO, J. Fisiologia de sementes de plantas cultivadas. Piracicaba: FEALQ, 2005. 495p.).

In evaluations performed at 14, 21 and 28 DAS, it can be seen that the temperatures of 20-30 °C and 25-35 °C stimulated the highest percentage of emerged seedlings, since more than 80% of the seeds of the cultivars BRS Sol do Cerrado and BRS Gigante Amarelo had already germinated at 14 DAS, with stability at 21 and 28 DAS, with emergence above 95% (Table 2). For the cultivar FB-200 Yellow Master, in spite of the stimulus of temperature increase on emergence, the values remained below 65% of emerged seedlings, which may be linked to the genetic difference between the passion fruit plant materials or the quality of the seed lot acquired.

Evaluation of the physiological quality of the seeds is an important manner of verifying the vigor of seed lots for commercialization purposes, in which each species or cultivar within the same species can express its maximum genetic potential (Pilau et al., 2012PILAU, F.G.; SOMAVILLA, L.; BATTISTI, R.; SCHWERZ, L.; KULCZYNSKI, S.M. Germinação de sementes de crambe em diferentes temperaturas e substratos. Semina: Ciências Agrárias , v.33, n.5, p.1825-1830, 2012. http://dx.doi.org/10.5433/1679-0359.2012v33n5p1825
http://dx.doi.org/10.5433/1679-0359.2012... ; Andrade and Jasper, 2013ANDRADE, R.A.; JASPER, S.P. Temperatura na emergência de quatro variedades de mamoeiro. Comunicata Scientiae, v.4, n.4, p.401-406, 2013. https://comunicatascientiae.com.br/comunicata/article/view/272/211
https://comunicatascientiae.com.br/comun... ). There are few studies showing the effect of temperature on germination of passion fruit plants (Passiflora edulis Sims). Pereira and Andrade (1994PEREIRA, T.S.; ANDRADE, A.C.S. Germinação de Psidium guajava L. e Passiflora edulis Sims - Efeito da temperatura, substrato e morfologia do desenvolvimento pós-seminal. Revista Brasileira de Sementes, v.16, n.1, p.58-62, 1994. http://www.abrates.org.br/revista/artigos/1994/v16n1/artigo12.pdf
http://www.abrates.org.br/revista/artigo... ), evaluating the thermal effect on seeds of fruits that were acquired in a fruit market, found that the highest percentage of emergence was achieved at the alteration of temperature of 20-30 °C.

The emergence speed index of the passion fruit seedlings increased with a rise in air temperature from 15-25 °C to 25-35 °C, while at a temperature below the minimum one cited, there was no seedling emergence (Table 2). It can be seen that the cultivar BRS Sol do Cerrado at the temperature amplitude of 25-35 °C had the highest absolute value of 3.069 in ESI, differing significantly from the other treatments. The lowest value of ESI was 0.643 for the cultivar FB-200 Yellow Master at the amplitude of 15-25 °C; however, there was an increase in the variable with a rise in thermal conditions, whereas in the cultivar BRS Gigante Amarelo, the ESI rose from 1.189 to 2.854.

For MET, the shortest times were obtained at the temperature of 25-35 °C, with mean values of 8.13 and 8.93 days for the cultivars BRS Sol do Cerrado and BRS Gigante Amarelo, respectively, and 10.5 days for the cultivar FB-200 Yellow Master (Table 2). Reduction in temperature increased the mean germination time, regardless of the cultivar, with values of 17.33 days at the temperature of 15-25 °C; at temperature ranges below this, there was no seedling emergence.

The superiority in ESI and the shorter MET at higher temperatures may be related to an increase in imbibition of water supplied by irrigation (Figure 1) as a result of an increase in temperature of the medium, leading to increases in diffusion pressure and in metabolic and enzymatic reactions (Marini et al., 2012MARINI, P.; MORAES, C.L.; MARINI, N.; MORAES, D.M.; AMARANTE, L. Alterações fisiológicas e bioquímicas em sementes de arroz submetidas ao estresse térmico. Revista Ciência Agronômica, v. 43, n. 4, p. 722-730, 2012. http://dx.doi.org/10.1590/S1806-66902012000400014
http://dx.doi.org/10.1590/S1806-66902012... ; Taiz and Zeiger, 2013TAIZ, L.; ZEIGER, E. Fisiologia vegetal. Porto Alegre: Artmed , 2013. 954p.) and reducing the internal water potential of the seed, allowing greater water uptake and better hydration (Bewley et al., 2014BEWLEY, J.D.; BRADFORD, K.J.; HILHORST, H.W.M.; NONOGAKI, H. Seeds: physiology of development, germination and dormancy. New York: Springer, 2014. 407p.; Taiz and Zeiger, 2013TAIZ, L.; ZEIGER, E. Fisiologia vegetal. Porto Alegre: Artmed , 2013. 954p.). In other tropical fruit-bearing plants, higher emergence speed indexes have been obtained in high temperature conditions, as observed by Zucareli et al. (2015ZUCARELI, V.; HENRIQUE, L.A.; ONO, E.O. Influence of light and temperature on the germination of Passiflora incarnata L. seeds. Journal of Seed Science , v.34, n.2, p.162-167, 2015. http://dx.doi.org/10.1590/2317-1545v37n2147082
http://dx.doi.org/10.1590/2317-1545v37n2... ) in a wild species of passion fruits (Passiflora incarnata L.) and by Ferraz et al. (2012FERRAZ, I.D.K.; ALBUQUERQUE, M.C.F.; CALVI, G.P.; FARIAS, D.L. Critérios morfológicos e temperatura para avaliação da germinação das sementes de cupuaçu. Revista Brasileira de Fruticultura , v.34, n.3, p.905-914, 2012. http://dx.doi.org/10.1590/S0100-29452012000300033
http://dx.doi.org/10.1590/S0100-29452012... ) in cupuaçu [Thebroma grandiflorum (Wild. ex. Spreng.)].

The total length (TL) and the shoot length (SL) of the passion fruit seedlings exhibited a significant difference among the cultivars and according to the thermal conditions to which they were subjected, in which temperatures less than or equal to the amplitude of 10-20 °C did not register values for these variables (Table 2).

Under the thermal conditions of 15-25 °C and 20-30 °C, the cultivar BRS Sol do Cerrado has higher values of TL and SL in relation to the other cultivars evaluated. However, at the temperature of 25-35 °C, there was no statistical difference between the cultivars BRS Sol do Cerrado (TL - 10.79 cm and SL - 6.01 cm) and BRS Gigante Amarelo (TL - 10.61 cm and SL - 5.75 cm), whereas the cultivar FB-200 had the lowest values of TL and SL, regardless of the temperature established. This response may be related to the genetic difference among the cultivars tested, the physiological quality of the seeds, or the dormancy process, which is present in most of the species of the Passifloracea family (Welter et al., 2011WELTER, M.K.; SMIDERLE, O.J.; UCHÔA, S.C.P.; CHANG, M.T.; MENDES, E.P. Germinação de sementes de maracujá amarelo azedo em função de tratamentos térmicos. Revista Agro@mbiente On-line, v.5, n.3, p.227-232, 2011. http://dx.doi.org/10.18227/1982-8470ragro.v5i3.626
http://dx.doi.org/10.18227/1982-8470ragr... ).

Taiz and Zeiger (2013TAIZ, L.; ZEIGER, E. Fisiologia vegetal. Porto Alegre: Artmed , 2013. 954p.) and Oliveira and Lemes (2014OLIVEIRA, A.K.M.; LEMES, F.T.F. Germinação de sementes e formação de plântulas de Lafoensia pacari sob diferentes temperaturas. Comunicata Scientiae , v.5, n.4, p.471-477, 2014. https://comunicatascientiae.com.br/comunicata/article/view/148
https://comunicatascientiae.com.br/comun... ) report that the increase in the thermal conditions of the air leads to an increase in metabolic activities, accelerating not only the germination process, but also embryo growth, with the mean temperature of 30 °C being the optimum temperature for growth and development of most of the species (Ferreira and Borghetti, 2004FERREIRA, A.G., BORGHETTI, F. Germinação: do básico ao aplicado. Porto Alegre: Artmed, 2004. 323 p.).

The individual dry matter of the seedling was affected by the increase in air temperature, as can be seen in Table 3. The increase in the thermal amplitude from 15-25 °C to 20-30 °C raised it from 8.931 to 11.588 mg, representing gains of 29.75%. At low temperatures, Marcos-Filho (2005)MARCOS-FILHO, J. Fisiologia de sementes de plantas cultivadas. Piracicaba: FEALQ, 2005. 495p. reports that seed respiration occurred in a slower manner and the reserves are not used in a rapid manner, which may have negatively affected the use of these reserves by the seedlings of the passion fruit cultivars, interfering in dry weight gain.

Upon subjected the seedlings to the highest temperature (25-35 °C), a reduction in seedling dry matter of 21.80% was observed, even though a statistical difference between the ranges 20-30 °C and 25-35 °C was not observed. Temperatures considerably higher than the optimum temperature for seedling growth and development contribute to degenerative transformations that bring about rapid consumption of seed reserves, which may affect respiration efficiency, leading to lower utilization in synthesis processes, with direct reflection on biomass accumulation in the seedlings (Patané et al., 2006PATANÉ, C.; CAVALLARO, V.; AVOLA, G.; D’AGOSTA, G. Seed respiration of sorghum [Sorghum bicolor (L.) Moench] during germination as affected by temperature and osmoconditioning. Seed Science Research, v.16, n.4, p.251-260, 2006. http://dx.doi.org/10.1017/SSR2006259
http://dx.doi.org/10.1017/SSR2006259 ... ; Marini et al., 2012MARINI, P.; MORAES, C.L.; MARINI, N.; MORAES, D.M.; AMARANTE, L. Alterações fisiológicas e bioquímicas em sementes de arroz submetidas ao estresse térmico. Revista Ciência Agronômica, v. 43, n. 4, p. 722-730, 2012. http://dx.doi.org/10.1590/S1806-66902012000400014
http://dx.doi.org/10.1590/S1806-66902012... ).

Conclusions

The seeds of passion fruit cultivars germinate more quickly and promote greater stability of seedling emergence in the temperature ranges of 20-30 °C and 25-35 °C due to a greater rate in the process of water uptake by the seeds;

The range of 20-30 °C stimulates the emergence, growth, and greater accumulation of dry matter of the seedlings;

Temperature alternating between 5-15 °C and 10-20 °C inhibit germination, emergence, and seedling growth of passion fruit seedlings of all the cultivars analyzed.

Acknowledgments

The authors thank the ‘Conselho Nacional de Desenvolvimento Científico e Tecnológico’ (CNPq) for granting a scholarship to the first author and the ‘Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)’ for financial support (APQ-01655-14).

References

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