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Germination of Stigmaphyllon blanchetii Seeds in Different Temperatures and Luminosity

Germinação de Sementes de Stigmaphyllon blanchetii em Diferentes Temperaturas e Luminosidade

ABSTRACT:

The objective of the present work was to study the influence of temperature and light on germination of seeds of Stigmaphyllon blanchetii, popularly known as rat tail. The first stage of the research evaluated the effect of three constant temperatures (20 oC, 25 oC and 30 oC) and an alternating temperature (20-30 oC). In the second stage, for simulation of different types of light, four conditions of luminosity (white, red, far red and absence of light) were used. The temperatures that provided the best germination and development for S. blanchetii are the constant (30 oC) and the alternating (20-30 oC) ones. The seeds germinated both in the presence and absence of light, but there was greater germination and seedling development in the absence of light; thus they were classified as preferential negative photoblastic seeds.

Keywords:
weed; Stigmaphyllon blanchetii; photoblastism; phytochrome

RESUMO:

O presente trabalho teve por objetivo estudar a influência da temperatura e da luz sobre a germinação das sementes de Stigmaphyllon blanchetii, conhecida popularmente como rabo-de-rato. Na primeira etapa da pesquisa, foi avaliado o efeito de três temperaturas constantes (20 oC, 25 oC e 30 oC) e uma alternada de 20-30 oC. Na segunda etapa, para simulação da luz sob diferentes qualidades espectrais, foram utilizadas quatro condições de luminosidade (luz branca, luz vermelha, vermelho distante e ausência de luz). As temperaturas que proporcionaram melhor germinação e desenvolvimento para S. blanchetii foram a constante de 30 oC e alternada de 20-30 oC. As sementes germinaram tanto na presença como na ausência de luz, porém houve maior germinação e desenvolvimento das plântulas na ausência de luz, podendo ser classificadas em fotoblásticas negativas preferenciais.

Palavras-chave:
planta daninha; rabo-de-rato; fotoblastismo; fitocromo

INTRODUCTION

Stigmaphyllon blanchetii C.E. Anderson, popularly known as rat tail, is a climber plant belonging to the family Malpighiaceae, native to Brazil, typical of the Northeast region. It is found in areas of tablelands, mainly in sugar cane crop areas (Lorenzi, 2008Lorenzi H. Plantas daninhas do Brasil: terrestres, aquáticas, parasitas e tóxicas. 4ª ed. Nova Odessa: Instituto Plantarum; 2008. ). Its distribution and adaptation for the Northeast region is concentrated in the states of Alagoas, Bahia, Paraíba, Pernambuco, Rio Grande do Norte and Sergipe. This species also occurs in the Southeastern region, in the states of Espírito Santo and Minas Gerais (REFLORA, 2018REFLORA. Flora do Brasil 2020 em construção. Jardim Botânico do Rio de Janeiro; 2018. [acesso em: 16 maio 2018]. Available at: Available at: http://floradobrasil.jbrj.gov.br/ .
http://floradobrasil.jbrj.gov.br/...
).

Weeds alter the structure of the ecosystem in which they are inserted (Minchinton et al., 2006Minchinton TE, Simpson JC, Bertness MD. Mechanisms of exclusion of native coastal marsh plants by an invasive grass. J Ecol. 2006;94:342-54.). They compete with crops of economic interest for environmental resources, such as water, light, nutrients and space (Gorchov and Trisel, 2003Gorchov DL, Trisel DE. Competitive effects of the invasive shrub, Lonicera maackii (Rupr.) Herder (Caprifoliaceae), on the growth and survival of native tree seedlings. Plant Ecol. 2003;166:13-24.), thus decreasing plant growth and profitability. Therefore, more detailed knowledge is needed about the biology of the study species.

The germination test of weed seeds is an essential tool that provides further knowledge about the biology of species, their ecological function in the field, adaptation capacity, and potential of infestation, for the purpose of further development of management strategies (Bastiani et al., 2015Bastiani MO, Lamego FP, Nunes JP, Moura DS, Wickert RJ, Oliveira JI. Germinação de sementes de capim-arroz submetidas a condições de luz e temperatura. Planta Daninha. 2015;33:395-404.). Germination is regulated by many factors, such as seed viability, seed dormancy and environmental conditions. Temperature can affect it directly or indirectly, through dormancy breaking, embryonic growth potential, deterioration, water absorption rate and biochemical reactions of the germination process (Marcos Filho, 2015Marcos Filho J. Fisiologia de sementes de plantas cultivadas. Londrina: ABRATES; 2015. ). Light is also a significant factor which controls the beginning of germination of photosensitive seeds, and phytochromes are responsible for perception and transduction of the light signal. This chromoprotein has two interconvertible forms: an inactive form, which is activated while absorbing the red light, inducing the production of Ga3 and triggering the beginning of germination, and an active state, which is inactivated when illuminated with far-red light, with consequent production of abscisic acid (ABA), inducing the seeds to a photodormant state (Takaki, 2001Takaki M. New proposal of classification of seeds based on forms of phytochrome instead of photoblastism. Rev Bras Fisiol Veg. 2001;13:104-8.; Seo et al., 2009Seo M, Nambara E, Choi G, Yamaguchi S. Interaction of light and hormone signals in germinating seeds. Plant Molec Biol. 2009;29:463-72.).

Plants can be classified according to their need of light for occurrence of germination: some need light to germinate (positive photoblastic), some require absence of light (negative photoblastic) and some are considered to be neutral, i.e., light does not interfere in the germination process (neutral photoblastic) (Galindo et al., 2012Galindo EA, Alves EU, Silva KB, Barrozo LM, Moura SSS. Germinação e vigor de sementes de Crataeva tapia L. em diferentes temperaturas e regimes de luz. Rev Cienc Agron. 2012;43:138-45.; Marcos Filho, 2015Marcos Filho J. Fisiologia de sementes de plantas cultivadas. Londrina: ABRATES; 2015. ). There are situations in which seeds are classified as preferentially positive photoblastic (quantitative character), because they also germinated in the absence of light (Klein & Felippe, 1991Klein A, Felippe GM. Efeito da luz na germinação de sementes de ervas invasoras. Pesq Agropec Bras. 1991;26:955-66.; Melo et al., 2014Melo PRB, Oliveira JA, Guimarães RM, Pereira CE, Pinto JEBP. Germinação de aquênios de Lychnophora pinaster em função de estádios de maturação, temperatura e luz. Científica. 2014;42:404-10.). As regards phytochrome forms, there are positive photoblastic seeds, whose PhyB controls germination through low fluency response; negative photoblastic seeds, in which PhyA controls germination through high irradiance response; and light insensitive seeds, whose PhyA controls germination through very low fluence response (Takaki, 2001Takaki M. New proposal of classification of seeds based on forms of phytochrome instead of photoblastism. Rev Bras Fisiol Veg. 2001;13:104-8.).

Light requirements vary across weed species: Conyza bonariensis and Conyza canadensis are positive photoblastic (Vidal et al., 2007Vidal RA, Kalsing A, Goulart ICGR, Lamego FP, Christoffoleti PJ. Impacto da temperatura, irradiância e profundidade das sementes na emergência e germinação de Conyza bonariensis e Conyza canadensis resistentes ao glyphosate. Planta Daninha. 2007;25(2):309-15.); the species I. grandifolia, I. nil and Merremia aegyptia, are negative photoblastic (Orzari et al., 2013Orzari I, Monquero PA, Reis FC, Sabbag RS, Hirata ACS. Germinação de espécies da família convolvulaceae sob diferentes condições de luz, temperatura e profundidade de semeadura. Planta Daninha. 2013;31(1):53-61.); and Sorghum halepense and Sorghum arundinaceum are neutral photoblastic (Krenchinski et al., 2015Krenchinski FH, Albrecht AJP, Albrecht LP, Villetti HL, Orso G, Barroso AAM, et al. Germination and dormancy in seeds of Sorghum halepense and Sorghum arundinaceum. Planta Daninha, 2015;33(2):223-30.).

In natural environments, there is variation of light and temperature, which can be changed by canopy structure. When reaching the soil, solar radiation is changed because of selective absorption of leaves, especially chlorophylls (Smith, 2000Smith H. Phytochromes and light signal perception by plants - an emerging synthesis. Nature. 2000;407:585-91. ), resulting in a low red:far-red ratio in the filtered light (Fenner, 1995Fenner M. Ecology of seed banks. In: Kigel J, Galili G, editors. Seed development and germination. New York: Dekker; 1995. p.507-28 ); thus, there is inhibition of seed germination of pioneer species (Válio and Joly, 1979Válio IFM, Joly CA. Light sensivity of the seeds on the distribuition of Cecropia glaziovi Snethlage (Moraceae). Zeitsch Pflanzenphysiol. 1979;91:371-6.). The seeds of positive photoblastic species, which are present at deeper layers in the seed bank, do not receive light; thus, they are not able to respond to fluctuations in temperature. However, the same seeds, when placed on the soil surface, but under shade, also did not respond to changes in temperature because they were in the absence of light (Ghersa et al., 1992Ghersa CM, Benech RL, Martinez-Ghersa MA. The role of fluctuating temperatures in germination and establishment of Sorghum hapelense. Regulation of germination at increasing depths. Func Ecol. 1992;66:460-8. ).

In addition, few studies to date have reported information on the biology of rat tail seeds. Thus, the objective of this work was to study the effects of temperature and light on germination of Stigmaphyllon blanchetii seeds.

MATERIAL AND METHODS

Fruit collection

The fruits of S. blanchetii were collected at various points in sugarcane crop areas, in the town of Atalaia, in the state of Alagoas (Brazil). Table 1 shows the geographical coordinates of the collection sites. The fruits were collected when they were in the senescence stage. After fruit collection, in all areas, through a simple sample, the composite sample was prepared for analysis. In the laboratory, the seeds were sterilized with sodium hypochlorite solution at 1% for two minutes, and afterwards they were cleansed with distilled water (Ferreira, 2001Ferreira RA, Soraya AB, Davide AC, Malavasi MM. Morfologia de frutos, sementes, plântulas e plantas jovens deDimorphandra mollisBenth. - faveira (Leguminosae - Caesalpinioideae). Rev Bras Bot. 2001;24(3):303-9.). The seeds were stored for 15 days after collection in ambient temperature until use.

Table 1
Geographical coordinates in UTM (Universal Transverse Mercator) of collection sites of Stigmaphyllon blanchetii fruits

Temperature test

The first test evaluated germination of Stigmaphyllon blanchetii seeds on the basis of temperature. The test used a completely randomized design, with five replicates of 20 seeds. Constant temperatures of 20 oC, 25 oC, 30 oC and alternate temperature of 20-30 oC were used under a 12-hour photoperiod. The seeds were placed in transparent plastic boxes (13 x 11 x 5 cm) containing sterile germitest paper as substrate, previously moistened with distilled water equivalent to 2.5 times the weight of the dry paper, which was remoistened when necessary (Brasil, 2009Brasil. Ministério da Agricultura, Pecuária e Abastecimento. Regras para análise de sementes. Brasília, DF: 2009. 399p.).

Light test

In the second test, the seeds of the study species were incubated in a germinator set at the alternating temperature of 20-30 oC, under different types of light (white, red, far red) or in the absence of light. The different types of light were obtained by combining red and blue cellophane paper. For the red light, the transparent plastic boxes were covered with two sheets of red cellophane paper, and for the far-red light, they were covered with overlapped sheets of red and blue cellophane paper. For the white light, transparent plastic boxes were used. They were kept inside closed plastic bags to prevent dehydration (Coimbra et al., 2007Coimbra RA. Teste de germinação com acondicionamento dos rolos de papel em sacos plásticos. Rev Bras Semen. 2007;29:92-7.). Absence of light was obtained by using black plastic boxes, and the counts were made under green light.

Germinated seeds were counted daily for a period of 25 days. Seeds were considered as germinated when they had primary root protrusion (Carvalho and Nakagawa, 2012Carvalho NM, Nakagawa J. Sementes: ciência, tecnologia e produção. 5ª.ed. Jaboticabal: FUNEP; 2012.). At the end of the evaluations, counts were made for number of normal seedlings (NS), shoot length (SL) and root length (RL), germination speed index (GSI), mean germination time (MGT) and dry matter (DM), for both experiments (Nakagawa, 1999; BRASIL, 2009).

The statistical design was completely randomized with five replications of 20 seeds.

Statistical analysis

Analysis of variance was made with the original data, comparing the means by Tukey’s test at 5% probability, using the software SISVAR (Ferreira, 2011Ferreira DF. Sisvar: A computer statistical analysis system. Cienc Agrotecnol. 2011;35:1039-42.). For completion of analysis of variance, data on germination percentage were subjected to arcsine transformation , and after that, all data were transformed into (Costa et al., 2010Costa PA, Lima ALS, Zanella F, Freitas H. Quebra de dormência em sementes de Adenanthera pavonina L. Pesq Agropec Trop. 2010;40(1):83-8. ).

RESULTS AND DISCUSSION

Stigmaphyllon blanchetii seeds showed distinct behaviors in their germination when subjected to different temperatures. The highest germination percentages occurred between 20 and 30 oC, and they were not different at the temperature of 30 oC. The same behavior also occurred in all study variables (Table 2). Thus, these temperatures can be considered as the most favorable to germination of this species.

Table 2
Germination percentage (G), germination speed index (GSI), mean germination time (MGT), normal seedling (PN), dry matter (DM), shoot length (SL) and root length (RL) of Stigmaphyllon blanchetii on the basis of different temperatures

An optimum temperature results from the combination of percentage and speed of germination, which have the most satisfactory results (Marcos Filho, 2015Marcos Filho J. Fisiologia de sementes de plantas cultivadas. Londrina: ABRATES; 2015. ). In this case, the constant temperature of 30 oC and the alternating temperature (20-30 oC) yielded higher results for percentage and speed of germination. There are species that have higher rates of germination when subjected to alternating temperatures, which is indicative of their ability to adapt to temperature variations of the environment (Martins et al., 2010Martins BAB, Chamma HMCP, Dias CTS, Christoffoleti PJ. Germinação de Borreria densiflora var. latifolia sob condições controladas de luz e temperatura. Planta Daninha. 2010;28(2):301-7.). Similarly to these results, Silva et al. (2017Silva RM, Matos VP, Farias SGG, Sena LHM, Silva DYBO. Germinação e vigor de plântulas de Parkia platycephala Benth. em diferentes substratos e temperaturas. Rev Cienc Agron. 2017;48:142-50.) found that Parkia platycephala seeds showed higher germination and vigor at alternating temperatures, which shows that this species tolerates adverse conditions and, thus, it has a higher percentage of success in the field.

There are several conditions that affect seed germination, and temperature is a factor that can interfere in water absorption speed, in germination speed and uniformity, and in chemical reactions that occur during the process (Marcos Filho, 2005; Carvalho and Nakagawa, 2012Carvalho NM, Nakagawa J. Sementes: ciência, tecnologia e produção. 5ª.ed. Jaboticabal: FUNEP; 2012.). The preference of S. blanchetii for alternating temperatures may be due to the conditions achieved during its process of formation and seed development, and the optimum temperature for germination is associated with ecological characteristics of the species (Probert, 1992Probert RJ. The role of temperature in germination ecophysiology. In: Fenner M. Seeds: the ecology of regeneration in plant communities. Wallingford: CABI; 1992. p.285-325.).

Temperatures higher or lower than the optimum temperature decrease germination speed, which can cause total reduction of germination (Carvalho and Nakagawa, 2012Carvalho NM, Nakagawa J. Sementes: ciência, tecnologia e produção. 5ª.ed. Jaboticabal: FUNEP; 2012.). When the seeds of S. blanchetii were subjected to temperatures of 20 oC and 25 oC, they showed a significant reduction in germination percentage, GSI, MGT, NS, DM, SL and RL. Thus, they were not indicated for the seed germination test of this species. A similar behavior was found by Zucarelli et al. (2015Zucarelli V, Henrique LAV, Ono EO. Influence of light and temperature on the germination of Passiflora incarnata L. seeds. J Seed Sci. 2015;37:162-7.) in Passiflora incarnata seeds, whose germinability was higher as germination increased, especially at 35 oC and at the alternating temperature of 30-20 oC.

Similar results were found by Martins et al. (2010Martins BAB, Chamma HMCP, Dias CTS, Christoffoleti PJ. Germinação de Borreria densiflora var. latifolia sob condições controladas de luz e temperatura. Planta Daninha. 2010;28(2):301-7.): the alternating temperature of 20-30 oC promoted the highest germination percentage in seeds of Borreria densiflora var. latifolia, and speed was inhibited when they were incubated at a temperature of 20 oC. Unlike such results, the temperatures of 20 oC and 25 oC provided higher percentage and speed of germination in seeds of Ipomea grandifolia, Ipomea nil and Merremia aegyptia (Orzari et al., 2013Orzari I, Monquero PA, Reis FC, Sabbag RS, Hirata ACS. Germinação de espécies da família convolvulaceae sob diferentes condições de luz, temperatura e profundidade de semeadura. Planta Daninha. 2013;31(1):53-61.), corroborating the findings of Borges and Rena (1993Borges EEL, Rena AB. Germinação de sementes. In: Aguiar IB, Piña-Rodrigues FCM, Figliolia MB, coordenadores. Sementes florestais tropicais. Brasília DF: ABRATES; 1993. p.83-136.), i.e., seeds have a variable behavior depending on temperature, and there is no optimum temperature and uniform germination for all species.

Mean germination time shows the time required for maximum germination to occur; the shorter the time, the higher the SGI. There was a reduction in MGT according to the increase of temperature; there was no statistical difference between the temperatures of 30 oC and 20-30 oC, which showed the lowest values (Table 1). This fact is indicative that these temperatures not only increased germination percentage and germination speed index, but also made germination faster. These results corroborate those of Alves et al. (2015Alves CZ, Silva JB, Candido ACS. Metodologia para a condução do teste de germinação em sementes de goiaba. Rev Cienc Agron. 2015;46:615-21.) in seeds of Psidium guajava. They found that the highest GMT values occurred at 20 oC and the lowest, at temperatures between 20 and 30 oC.

For percentage of normal seedlings, at a temperature of 20 oC and 25 oC, there was a reduction in the number of normal seedlings and in root and shoot length. This was possibly due to the fact that low temperatures cause changes in cell structure, including the plasma membrane and the cell wall. Moreover, they reduce relative plant growth and increase the amount of flavonoids (Matsuura and Obata, 1993Matsuura M, Obata A. Glucosidases from soybean hydrolyze daidzin and genistin. J Food Sci. 1993;58:144-7. ; Lozovaya et al., 2005Lozovaya VV, Lygin AV, Ulanov AV, Nelson RL, Daydé J, Widholm JM. Effect of temperature and soil moisture status during seed development on soybean seed isoflavone concentration and composition. Crop Sci. 2005;45:1934-40. ).

Also, the analysis of seedling length (shoot + root) showed that the temperature of 30 oC and the alternate temperature of 20-30 oC led to balanced shoot and root growth, while at the other temperatures, there was increased root production but decreased shoot production. Mean shoot length and mean root length are key variables to identify the most vigorous plants in the germination test. Differences between the analyzed treatments were relative to more vigorous plants as a result of differential growth and, therefore, there was maximum dry matter production (Nakagawa, 1999Nakagawa J. Testes de vigor baseados no desempenho das plântulas. In: Krzyzanoski FC, Vieira RD, França Neto JB, editores. Vigor de sementes: conceitos e testes. Londrina: ABRATES; 1999. p.1-24.).

The results of plant dry matter showed that the seeds subjected to temperatures of 30 oC and 20-30 oC had the best results. According to Freitas et al. (2009Freitas FCL, Almeida MEL, Negreiros MZ, Honorato ARF, Mesquita HC, Silva SVOF. Períodos de interferência de plantas daninhas na cultura da cenoura em função do espaçamento entre fileiras. Planta Daninha. 2009;27(3):473-80.), seedling dry matter values enable an evaluation of growth because plants have greater or lesser competitive capacity. At these temperatures, S. blachetii seedlings showed higher dry matter values, and their competitive capacity was greater. There is greater production at short intervals and there is an advantage in competition for available resources, which may retard or suppress growth of other plants. Thus, it can be inferred that S. blanchetii seeds have better conditions of development when exposed to a temperature of 30 oC or alternate temperature between 20 and 30 oC.

Light is another factor that is connected with germination; it can be influenced by temperature in some cases, and germination may not occur (Santos and Pereira, 1987Santos DSB, Pereira MFA. Gemination of seeds of two cultivars of sugarbeet: effect of light and temperature. Braz J Bot. 1987;10:15-20.). In this sense, by evaluating the influence of light and temperature on the development of Amburana cearenses, Almeida et al. (2017Almeida JPN, Lessa BFT, Pinheiro CL, Gomes FM, Medeiros Filho S, Silva CC. Germination and development of Amburana cearensis seedlings as influenced by seed weight, light and temperature. Acta Sci. 2017;39:525-33.) found that the species has better growth when under a temperature of 25 oC and 30 oC and in the presence of light.

As regards the influence of light, the largest percentages and speed of germination occurred when the seeds were under red light and absence of light, without differences among themselves, while white light caused lower germination percentage and germination speed index. However, with far-red light, there was no difference in the remaining luminosities for germination purposes (Table 3). These results are different from those of Thomas (1974Thomas H. Control mechanism in the resting seeds. In: Roberts EH, editor. Viability of seeds. London: Chapman and Hall; 1974. p.360-96.) and Alves et al. (2016Alves MM, Alves EU, Lima MLS, Rodrigues CM, Silva BF. Germinação de sementes de Platymiscium floribundum vog. (Fabaceae) sob a influência da luz e temperaturas. Cienc Flor. 2016;26:971-8.), who reported that red light provides a similar effect to that of white light in spectral composition and absorption characteristics of phytochromes.

Table 3
Germination percentage (G), germination speed index (GSI), mean germination time (MGT), normal seedling (PN), dry matter (DM), shoot length (SL) and root length (RL) of Stigmaphyllon blanchetii, on the basis of different types of light, at a temperature of 20-30 oC

Alves et al. (2012Alves MM, Alves EU, Bruno RLA, Silva KRG, Moura SSS, Barrozo LM, Araújo LR. Potencial fisiológico de sementes de Clitoria fairchildiana R. A.Howard. - Fabaceae submetidas a diferentes regimes de luz e temperatura. Cienc Rural. 2012;42:2199-205.) found different results: in Clitoria fairchildiana seeds under alternating temperatures of 20-30 oC, there was no difference in germination percentage when they were subjected to different spectral qualities, while germination speed was lower when the seeds were exposed to absence of light.

This germination behavior under different types of light can be influenced by the active form of the phytochrome present in seeds in sufficient quantity to start the germination process. In principle, the phytochrome is inactive (710 nm); when absorbing red light, it becomes active (660 nm), thereby initiating germination, together with other factors, such as hormone synthesis and activation of genetic transcription (Bewley et al., 2013Bewley JD, Bradford K, Hilhorst H. Seeds: Physiology of development, germination and dormancy. 3rd ed. New York: Springer; 2013.; Marcos Filho, 2015Marcos Filho J. Fisiologia de sementes de plantas cultivadas. Londrina: ABRATES; 2015. ).

Importantly, there was a reduction in mean germination time as the germination speed index increased (Table 3). For the seeds kept in the dark, MGT was shorter when compared to that of seeds kept in the light (Table 3). Sida rhombifolia seeds also have lower MGT values in the absence of light, which makes germination slower (Carvalho and Carvalho, 2009Carvalho DB, Carvalho RIN. Qualidade fisiológica de sementes de guanxuma em influência do envelhecimento acelerado e da luz envelhecimento acelerado e da luz. Maringá. 2009;31(3):489-94.). According to Labouriau and Agudo (1987Labouriau FGA, Agudo M. On the physiology of germination inSalvia hispanicaL. temperature effects. An Acad Bras Cienc, 1987;59:57-69. ), this delay in germination may increase the likelihood that seedlings will find favorable conditions for development.

It was found that the seeds kept in the dark showed higher values for seedling shoot length, when compared with those incubated in the light. In the absence of light, seeds need to use more of their reserves for shoot elongation in the search for light in order to start photosynthesis. This fact was observed in this study (Taiz and Zeiger, 2013Taiz L, Zeiger E. Fisiologia vegetal. 5ª.ed. Porto Alegre: Artmed; 2013. 954p. ). There was no difference for root length among seeds subjected to the presence and/or absence of light. Different results were found by Paiva et al. (2016Paiva EP, Torres SB, Sá FVS, Nogueira NW, Freitas RMO, Leite MS. Light regime and temperature on seed germination in Salvia hispanica L. Acta Sci. 2016;38:513-9.): Salvia hispanica seeds showed greater seedling growth and dry matter accumulation in the presence of light.

For dry matter, the best results were found in seeds incubated in red light and in the dark. The low dry matter values are related to the treatment with white light and far-red light (Table 3). This fact was possibly due to prolonged exposure of seedlings; high irradiance cause greater absorption of light photons than allowed, and as a result, there may occur photoinhibition and even plant death (Kitao et al., 2000Kitao M, Lei TT, Koike T, Tobita H, Maruyama Y. Susceptibility to photoinhibition of three deciduous broadleaf tree species with different successional traits raised under various light regimes. Plant Cell Environ. 2000;23:81-9.). Carvalho et al. (2006Carvalho NOS, Pelacani CR, Rodrigues MOS, Crepaldi IC. Crescimento inicial de plantas de Licuri (Syagrus coronata (Mart.) Becc.) em diferentes níveis de luminosidade. Rev Árvore. 2006;30(3):351-7.) found that, for Syagrus coronata, there was a reduction of seedling shoot dry matter as brightness increased. By contrast, Alves et al. (2012Alves MM, Alves EU, Bruno RLA, Silva KRG, Moura SSS, Barrozo LM, Araújo LR. Potencial fisiológico de sementes de Clitoria fairchildiana R. A.Howard. - Fabaceae submetidas a diferentes regimes de luz e temperatura. Cienc Rural. 2012;42:2199-205.) found that the dry matter of Clitoria fairchildiana roots, at alternating temperatures of 20-30 oC, was lower when subjected to the absence of light. Also, they reported higher dry matter values in the presence of far-red, red and white light. This may be explained by the fact that the most vigorous seeds have greater capacity to transfer their reservations to the embryonic axis, resulting in seedlings with a higher growth rate (Nakagawa, 1999Nakagawa J. Testes de vigor baseados no desempenho das plântulas. In: Krzyzanoski FC, Vieira RD, França Neto JB, editores. Vigor de sementes: conceitos e testes. Londrina: ABRATES; 1999. p.1-24.).

Seeds can be classified, according to need of light for germination to occur, into positive photoblastic, when they need light for germination; negative photoblastic, when germination occurs in the dark, and non-photoblastic or indifferent, when light does not interfere in the germination process (Marcos Filho, 2015Marcos Filho J. Fisiologia de sementes de plantas cultivadas. Londrina: ABRATES; 2015. ). For Klein and Felippe (1991Klein A, Felippe GM. Efeito da luz na germinação de sementes de ervas invasoras. Pesq Agropec Bras. 1991;26:955-66.) and Melo et al. (2014Melo PRB, Oliveira JA, Guimarães RM, Pereira CE, Pinto JEBP. Germinação de aquênios de Lychnophora pinaster em função de estádios de maturação, temperatura e luz. Científica. 2014;42:404-10.), the photoblastic character may have a preferential element (quantitative character), when there is a small amount of seeds germinated in the dark, or an absolute character, when germination only occurs in the presence of light. Thus, S. blanchetti seeds germinated in the presence and in the absence of light, but there was higher germination and seedling development in the absence of light. Thus, they may be possibly classified as negative photoblastic. The same behavior was found in Myracrodruon urundeuva seeds (Silva et al., 2002Silva LMM, Rodrigues TJD, Aguiar IB. Efeito da luz e da temperatura na germinação de sementes de aroeira (Myracrodruon urundeuva Allemão). Rev Árvore. 2002;26:691-7.). Echium plantagineum seeds are considered to be preferentially positive photoblastic (Roso et al., 2017Roso R, Nunes UR, Paranhos JT, Müller CA, Fernandes TS, Ludwig EJ. Germination of Echium plantagineum L. seeds submitted to dormancy overcoming and variations in temperature, light and depth of sowing. J Seed Sci. 2017;39:262-71.).

Seeds can also be classified according to light in relation to phytochrome forms. There was higher percentage and speed of germination when seeds were exposed to red light and absence of light; thus, this species probably has the phytochrome form phyA controlling germination through high irradiance (Takaki, 2001Takaki M. New proposal of classification of seeds based on forms of phytochrome instead of photoblastism. Rev Bras Fisiol Veg. 2001;13:104-8.). Different results were found by Stefanello et al. (2006Stefanello R, Garcia DC, Menezes NL, Muniz MFB, Wrasse CF. Efeito da luz, temperatura e estresse hídrico no potencial fisiológico de sementes de funcho. Rev Bras Sementes. 2006;28:135-41.), who found that seeds of Foeniculum vulgare Miller were indifferent to light, and phytochrome phyA was responsible for germination through very low fluence response. The same behavior was found by Alves et al. (2012Alves MM, Alves EU, Bruno RLA, Silva KRG, Moura SSS, Barrozo LM, Araújo LR. Potencial fisiológico de sementes de Clitoria fairchildiana R. A.Howard. - Fabaceae submetidas a diferentes regimes de luz e temperatura. Cienc Rural. 2012;42:2199-205.) in light-insensitive Clitoria fairchildiana seeds, since they have phytochromes controlling germination through very low fluence response. In Muntingia calabura seeds, phytochromes control germination through low fluence response (Leite and Takaki, 2001Leite ITA, Takaki M. Phytochrome and temperature control of seed germination in Muntingia calabura L. (Elaeocarpaceae). Braz Arch Biol Technol. 2001;44:297-302.).

Thus, Stigmaphyllon blanchetii seeds germinate and grow best at temperatures of 30 oC and 20-30 oC, preferably in the absence of light.

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Publication Dates

  • Publication in this collection
    04 Nov 2019
  • Date of issue
    2019

History

  • Received
    30 Apr 2018
  • Accepted
    02 Oct 2018
Sociedade Brasileira da Ciência das Plantas Daninhas Departamento de Fitotecnia - DFT, Universidade Federal de Viçosa - UFV, 36570-000 - Viçosa-MG - Brasil, Tel./Fax::(+55 31) 3899-2611 - Viçosa - MG - Brazil
E-mail: rpdaninha@gmail.com