In vitro germination and viability of pollen grain of coconut accessions1

Germinação in vitro e viabilidade de grãos de pólen de acessos de coqueiro

Catrine Regina Feitosa Moura Caroline de Araújo Machado Ana da Silva Lédo About the authors

Abstracts

Storage as a means of maintaining the pollen viability is important for the preservation of the genetic variability, facilitates the exchange of germplasm and greatly contributes to the generation of variability obtained from artificial crosses, increasing the efficiency of breeding programs. The objective of this study was to select different culture media for the in vitro germination of pollen grain of dwarf and tall coconut accessions, as well as to determine the viability of pollen grain at room temperature conditions. For this purpose, Brazil Green Dwarf (BGD) and Brazilian Tall (BRA) pollen grains derived from the Coconut Active Germplasm Bank of Embrapa Coastal Tablelands Sergipe were used. To evaluate the effect of different culture media on the in vitro germination of pollen grains of anão verde do Brasil de Jiqui (AVeBrJ) and gigante do Brasil Praia do Forte (GBrPF) accessions, they were inoculated on to Petri dishes containing 2 ml of culture media. The pollen viability was assessed by staining with 1% acetic carmine and in vitro germination at 0, 24, 48 and 72 hours. The culture medium of Lora is suitable to assess the in vitrogermination of pollen grain of the AVeBrJ and GBrPF accessions. The pollen grain of the AVeBrJ accession showed intermediate viability (66.87%) at room temperature up to 23.14 hours by in vitro germination. The pollen grain of the GBrPF accession showed high viability, above 70%, at room temperature up to 120 hours by in vitro germination.

Cocos nucifera ; In vitro culture; Culture media


A conservação de recursos genéticos é importante para a preservação da variabilidade genética, facilita o intercâmbio de germoplasma e contribui na geração de variabilidade obtida por meio de cruzamentos artificiais aumentando a eficiência dos programas de melhoramento genético. O objetivo desse estudo foi selecionar meio de cultura para germinação in vitro de grãos de pólen de acessos de coqueiro anão e gigante, bem como determinar a viabilidade de grãos de pólen em condições de temperatura ambiente. Para tanto foram utilizados grãos de pólen dos acessos Anão verde do Brasil de Jiqui (AVeBrJ) e Gigante do Brasil Praia do Forte (GBrPF) provenientes do Banco Ativo de Germoplasma de Coco da Embrapa Tabuleiros Costeiros. Para avaliar o efeito de diferentes meios de cultura na germinação in vitro, grãos de pólen dos acessos BGD e BRA foram inoculados em placas de Petri contendo 2 ml de meio de cultura. A viabilidade do pólen foi avaliada por coloração com 1% carmim acético e por germinação in vitro a 0, 24, 48 e 72 horas. O meio Lora promove o maior percentual de germinação in vitro de grãos de pólen dos dois acessos. Grãos de pólen do acesso AVeBrJ apresentam viabilidade intermediária (66,87%) no ponto máximo da curva de 23,14 horas por germinação in vitro. Os grãos de pólen do acesso GBrPF apresentaram alta viabilidade acima de 70% até 120 horas em temperatura ambiente por germinação in vitro.

Cocos nucifera ; Cultura in vitro; Meio de cultura


INTRODUCTION

Storage of pollen grains is important for the preservation of germplasm and to aid in research using stored biological materials to promote exchange and enhance breeding programs (HANNA, 1994HANNA, W. N. Pollen storage in frostless and conventional frost-forming freezers. Crop Science, v. 34, p. 1681-1682, 1994.). Furthermore, it is considered one of the main alternatives for the conservation of genotypes, which would allow carrying out crossings without the need for alternate cultivation of these pollinating strains in the field (GANESHAN et al, 1986GANESHAN, S. Viability and fertilizing capacity of onion pollen ( Allium cepa L.) stored in liquid nitrogen (-196° C). Topical Agricultural, v. 63, n. 1, p. 46-48, 1986.).

In palms, the study of pollen grain storage has received special attention due to the production of hybrids being held in pollen grains, fresh and preserved at low temperatures (KARUN et al, 2006KARUN, A. et al. Cryopreservation of coconut (Cocos nucifera L.) pollen. Journal of Plantation Crops, v. 3, n. 3, p. 568-571, 2006.; KARUN; SAJINI, 2010KARUN, A.; SAJINI, K. K. Cryopreservation of coconut zygotic embryos and pollen. Kasaragod: Central Plantation Crops Research Institute, 2010. 17 p. (Technical Bulletin, 63).; SOUSA; SCHEMBERG; AGUIAR, 2010SOUSA, V. A.; SCHEMBERG, E. A.; AGUIAR, A. V. Germinação in vitro do pólen de jerivá (Syagrus romanzoffiana (S.) Cham) Scientia Forestalis, v. 38, n. 86, p. 147-151, 2010.; TOWILL; WATERS, 2000TOWILL, L. E.; WALTERS, C. Cryopreservation of pollen. In: ENGELMANN, F.; TAKAGI, H. (Ed.) Cryopreservation of tropical plant germplasm: current research progress and application. Rome: IPGRI, p.115-129, 2000.). The evaluation of the germination capacity (viability) during the storage of pollen grains from the male parent is crucial in the process of artificial hybridization (FRANÇA et al,2009FRANÇA, L. et al. Viability of eggplant pollen. Crop Breeding & Applied Biotechnology, v. 9, n. 4, p. 320-327, 2009.).

For the intermediate and long-term storage success, one should master collecting, drying and storage techniques and pollen viability tests. For this, methodologies for these techniques must be developed, since each species behaves differently against these procedures, which can compromise pollen viability (SOUSA; SCHEMBERG; AGUIAR, 2010SOUSA, V. A.; SCHEMBERG, E. A.; AGUIAR, A. V. Germinação in vitro do pólen de jerivá (Syagrus romanzoffiana (S.) Cham) Scientia Forestalis, v. 38, n. 86, p. 147-151, 2010.).

The in vitro germination of pollen grains is the most applied technique for pollen viability studies (SOARES et al., 2008SOARES, T. L. et al. In vitrogermination and viability of pollen grains of banana diploids. Crop Breending and Applied Biotechnology, v. 8, p. 111-118, 2008.). Various culture media are used for in vitro pollen germination and the Brewbaker and Kwack medium (BREWBAKER; KWACK, 1963BREWBAKER, J. L.; KWACK, B. H. The essential role of calcium in pollen germination and pollen tube growth. American Journal of Botany, v. 50, n. 9, p. 859-865, 1963.) is the most widely applied. Changes in the boron and sucrose concentrations are necessary for optimal germination (TOWILL; WALTERS, 2000TOWILL, L. E.; WALTERS, C. Cryopreservation of pollen. In: ENGELMANN, F.; TAKAGI, H. (Ed.) Cryopreservation of tropical plant germplasm: current research progress and application. Rome: IPGRI, p.115-129, 2000.).

In palm, the specific conditions for pollen germination are wide and acceptable results are obtained with various sugars in liquid semi-solid culture media, with or without the addition of boric acid. In studies with areca palm (Areca catechu L.), tucumã palm (Astrocaryum vulgare Mart.) and queen palm (Syagrus romanzoffiana (S.) Cham) Liu, Huang and Li (2013)LIU, L.; HUANG, L.; LI, Y. Influence of boric acid and sucrose on the germination and growth of areca pollen. American Journal of Plant Sciences, v. 4, p. 1669-1674, 2013., Oliveira, Coutunier and Beserra (2003)OLIVEIRA, M. S. P.; COUTURIER, G.; BESERRA, P. Biologia da polinização da palmeira tucumã (Astrocaryum vulgare Mart.) em Belém-Pará, Brasil. Acta Botanica Brasílica, v. 17, n. 3, p. 343-353, 2003. and Sousa, Schemberg and Aguiar (2010)SOUSA, V. A.; SCHEMBERG, E. A.; AGUIAR, A. V. Germinação in vitro do pólen de jerivá (Syagrus romanzoffiana (S.) Cham) Scientia Forestalis, v. 38, n. 86, p. 147-151, 2010., respectively, observed high pollen viability. Ranasinghe et al. (2010)RANASINGHE, C. S. et al. Approach to Screen Coconut Varieties for High Temperature Tolerance by in-vitro Pollen Germination. Cocos, v. 19, n. 1, p. 1-11, 2010. quantified the response of in vitro pollen germination in Asian coconut varieties at different temperatures. There are not reports on the pollen grain viability of Brazilian coconut varieties.

The aim of this study was to select culture medium for the in vitrogermination of pollen grain of the anão verde do Brasil de Jiqui (AVeBrJ) and gigante do Brasil Praia do Forte (GBrPF) accessions and determine the viability of pollen grain at room temperature.

MATERIAL AND METHODS

Representative plants of anão verde do Brasil de Jiqui - AVeBrJ (Brazil Green Dwarf) and gigante do Brasil Praia do Forte - GBrPF (Brazilian Tall) accessions were select from the Coconut Active Germplasm Bank of Embrapa Coastal Tablelands Sergipe located at the experimental fields of Itaporanga and Betume, Sergipe, Brazil. For each plant, a spathe close to maturation was marked before opening, removed from the plants and maintained at room temperature in the laboratory (28 ± 1 °C) until anthesis. The pollen grains were collected and placed in cryotubes under room temperature.

To evaluate the effect of different culture media on the in vitrogermination of pollen grains of the AVeBrJ and GBrPF accessions, they were inoculated on to Petri dishes containing 2 ml of culture media (Table 1).

The Petri dishes were kept in biological incubator at 24 ±1 °C for a 24-hour period. In DMLS Leica microscope, 10X magnification and were analyzed at 0, 24, 48 and 72 hours after inoculation for the number of germinated pollen grains. The pollen grains were considered germinated when showing pollen tube length greater than their diameter. To calculate of in vitro pollen germination, the following formula was used:

Table 1
Composition of the culture media evaluated for in vitrogermination of coconut accessions

In vitro pollen germination (%) = Number of germinated pollen grains / Number of counted pollen grains x 100.

For the determination of the in vitro pollen grains viability, pollen grains released from male flowers of the AVeBrJ and GBrPF accessions as previously described were placed in cryotubes and kept under room temperature until the completion of each experimental trial.

The pollen grain viability by in vitro germination as previously described and by staining with 1% acetic carmine and in vitrogermination at the following times after pollen extraction: 0, 24, 48, 72, 96 and 120 hours for BGD and at 0, 24, 48, 96, 120, 168 and 216 hours for the BGD in daily inoculations in the culture medium of Lora et al. (2006)LORA, M. A. J. et al. Low temperature storage and in vitro germination of cherimoya (Annona cherimola Mill) pollen. Scientia Horticulturae, v. 1, n. 1, p. 91-94, 2006..

To assess the viability by staining, a pollen sample with approximately 0.02 grams was placed on a slide by adding a drop of 1% acetic carmine followed by homogenization. Then, the slide was placed in a Petri dish and kept in biological incubator at 37 ± 1 °C for 25-30 minutes. In microscope model DMSL (Leica, Bernsheim, Germany) at 10x magnification, with a digital camera model Moticam C2300 (Motic Instruments, Hong Kong, Chine) the slides were analyzed for number of viable and nonviable pollen grains per quadrant.

Pollen grains stained in red were considered viable (by the reaction of the presence of enzymatic activity) and with intact walls and nonviable, those colorless or stained in red with rupture of walls. To calculate of pollen grain viability, the following formula was used:

Pollen viability (%) = Number of stained pollen grains/Number of counted pollen grains x 100

The experimental design of culture medium selection was completely randomized in a 4 x 4 factorial scheme (four culture media combined with four evaluation times) and three replications. For in vitro viability test under room temperature, a completely randomized design with six treatments and three replicates was considered for the AVeBrJ accession and a completely randomized design with seven treatments and three replicates for the GBrPF accession.

The viability of pollen grain means were subject to an analysis of variance by F test at a 5% probability and were estimated the regression curves with SISVAR software (FERREIRA, 2011FERREIRA, D. F. SISVAR: a computer statistical analysis system. Ciência e Agrotecnologia, v. 35, n. 6, p. 1039-1042, 2011.).

RESULTS AND DISCUSSION

There was a significant interaction between culture media and time for the in vitro germination of the pollen grains of the AVeBrJ and GBrPF accessions (Table 2).

Table 2
Summary of the analyses of variance of the pollen grains viability of the AVeBrJ and GBrPF coconut accessions under different culture media (CM) and times (T)

The culture medium of Lora (LORA et al., 2006LORA, M. A. J. et al. Low temperature storage and in vitro germination of cherimoya (Annona cherimola Mill) pollen. Scientia Horticulturae, v. 1, n. 1, p. 91-94, 2006.) provided higher germination of the pollen tube for both accessions (Table 3 and Figura 1), being notably the best culture medium for studies on the viability of pollen grains by in vitro germination of the pollen tube for coconut accessions.

Table 3
Pollen grain viability of the AVeBrJ and GBrPF coconut accessions under different culture media and times by in vitro germination
Figure 1
General view of the in vitro pollen tube germination in the culture medium of Lora (10x): A- AVeBrJ accession; B- GBrPF accession

Probably, the high viability shown by pollen grains in the culture medium of Lora et al. (2006)LORA, M. A. J. et al. Low temperature storage and in vitro germination of cherimoya (Annona cherimola Mill) pollen. Scientia Horticulturae, v. 1, n. 1, p. 91-94, 2006. is due to the combination of boron, calcium, sucrose and its liquid physical condition. The basic culture medium used in most germination tests of pollen grains is composed of sucrose, and the combination of other nutrients may vary. Boron and calcium are essential for the onset of the intine prolongation and in vitro pollen tube formation (BREWBAKER; KWACK, 1963BREWBAKER, J. L.; KWACK, B. H. The essential role of calcium in pollen germination and pollen tube growth. American Journal of Botany, v. 50, n. 9, p. 859-865, 1963.).

Pio et al. (2007)PIO, L. A. S. et al. Viabilidade do pólen de laranjas doces em diferentes condições de armazenamento. Ciência e Agrotecnologia, v. 31, n. 1, p. 147-153, 2007. and Ramos et al. (2008)RAMOS, J. D. et al. Receptividad del estigma y ajuste del protocolo para la germinación in vitro de granos del polen en cítricos. Interciência, v. 33, n. 1, p. 51-55, 2008. observed that the boron concentration of 200 mg L-1 stimulated the germination of pollen grains of citrus cultivars.

However, the in vitro germination of apple pollen grains (Malus sp.) had no positive effective in the presence of boric acid (DANTAS et al., 2005DANTAS,A. C. de M. et al. Viabilidadedo pólen e desenvolvimento do tubo polínico em macieira (Malus ssp.). Revista Brasileira de Fruticultura, v. 27, n. 3, p. 356-359, 2005.). As previously mentioned, the addition of boron to the culture medium showed variable responses, depending on the species, and for the BRA and BGD accessions, the presence of boron was positive.

Some broken pollen tubes of the BRA accession in the presence of media of Sousa, Schemberg and Aguiar (2010)SOUSA, V. A.; SCHEMBERG, E. A.; AGUIAR, A. V. Germinação in vitro do pólen de jerivá (Syagrus romanzoffiana (S.) Cham) Scientia Forestalis, v. 38, n. 86, p. 147-151, 2010. and Sousa, Schemberg and Aguiar (2010)SOUSA, V. A.; SCHEMBERG, E. A.; AGUIAR, A. V. Germinação in vitro do pólen de jerivá (Syagrus romanzoffiana (S.) Cham) Scientia Forestalis, v. 38, n. 86, p. 147-151, 2010. modified were observed. According to Salles et al. (2006)SALLES, L. A. et al. Sacarose e pH na germinação in vitro de grãos de pólen de citros. Ciência e Agrotecnologia, v. 30, n. 1, p.170-174, 2006., pollen tubes may break due to high humidity and changes in the environment caused by increased osmotic pressure and low resistance of the cell wall. Boron stimulates pollen tube growth and decreases the likelihood of breaking up (FRANZON; RASEIRA, 2006FRANZON, R. C.; RASERA, M. C. B. Germinação in vitro e armazenamento de pólen de Eugenia involucrata DC. (Myrtaceae). Revista Brasileira de Fruticultura, v. 28, n. 1, p. 18-20, 2006.). The rupture observed in this study can be attributed to the absence of boron in the composition of the media of Sousa, Schemberg and Aguiar (2010)SOUSA, V. A.; SCHEMBERG, E. A.; AGUIAR, A. V. Germinação in vitro do pólen de jerivá (Syagrus romanzoffiana (S.) Cham) Scientia Forestalis, v. 38, n. 86, p. 147-151, 2010. and Sousa, Schemberg and Aguiar (2010)SOUSA, V. A.; SCHEMBERG, E. A.; AGUIAR, A. V. Germinação in vitro do pólen de jerivá (Syagrus romanzoffiana (S.) Cham) Scientia Forestalis, v. 38, n. 86, p. 147-151, 2010. modified.

Sousa, Schemberg and Aguiar (2010)SOUSA, V. A.; SCHEMBERG, E. A.; AGUIAR, A. V. Germinação in vitro do pólen de jerivá (Syagrus romanzoffiana (S.) Cham) Scientia Forestalis, v. 38, n. 86, p. 147-151, 2010. observed higher in vitro germination of queen palm pollen (Syagrus romanzoffiana (S.) Cham) in culture medium with 3 g L-1 agar and 100 g L-1 sucrose.

According to Stanley and Linskens (1974)STANLEY, R. G.; LINSKENS, H. F. Pollen: biology, biochemistry and management. New York: Springer - Verlag, 1974, 172 p., sucrose promotes osmotic balance between the pollen and the germination medium and provides energy to the development of the pollen tube. Reis et al. (2011)REIS, R. V. dos et al. Viabilidade in vitro de grãos de pólen de bananeira sob diferentes concentrações de ácido bórico e sacarose. Ciência e Agrotecnologia. v. 35, n. 3, p. 547-553, 2011. worked with banana pollen (Musa sp.) and observed that the standard culture medium for the germination of pollen grains supplemented with 15% sucrose provided higher germination percentage when compared to medium without sucrose and supplemented with 6.7% of the carbohydrate.

There was a significant effect of time on the viability by in vitrogermination of pollen grains of the AVeBrJ accession submitted at room temperature. There was no effect of time on the viability by staining (Table 4).

Table 4
Summary of the analyses of variance of the pollen grain viability of the AVeBrJ and GBrPF coconut accessions in different times under room temperature by in vitro germination (GER) and staining with 1% acetic carmine (ACA)

The viability by in vitro germination of pollen grains of the AVeBrJ accession presented a quadratic variation with significant decrease after 23,14 hours. The viability by staining with 1% carmine acetic acid presented a cubic variation (Figure 2).

Figure 2
Response of the pollen grains viability of the AVeBrJ accession at different times under room temperature by in vitro germination and staining with 1% acetic carmine

The highest viability by in vitro germination of the pollen tube obtained by the maximum point of the regression curve was the 66.87% at 23.14 hours after inoculation.

The AVeBrJ accession reached the highest viability compared with results obtained by Armendariz et al. (2006)ARMENDARIZ, B. H. C. et al. Pollen fertility and female flower anatomy of micropropagated coconut palms. Revista Fitotécnica Mexicana, v. 29, n. 4, p. 373-378, 2006. for Malayan green dwarf (MGD) coconut. This reinforces that viability depends on the genotype and other factors, as reported by Ganeshan et al. (2008)GANESHAN, S. et al. Cryopreservation of pollen. In: REED, B.M. (Ed.) Plant cryopreservation: a practical guide. New York: Springer, p. 443-447. 2008.. InPassiflora suberosa, Cruz et al. (2008)CRUZ, T. V et al. Germinação in vitrode grãos de pólen emPassiflora suberosa L. para sua utilização em hibridação interespecífica. Revista Brasileira de Fruticultura, v. 30, n. 4, p. 875-879, 2008. the viability obtained by in vitro germination showed smaller value (21.82%).

There was a significant effect of time on the viability of pollen grains of the GBrPF accession by germination of the pollen tube and by staining at room temperature (Table 4). The viability by in vitro germination presented a decrease linear with values above 70% up to 120 hours and the viability by staining with 1% carmine acetic acid presented a quadratic variation with significant decrease after 109.81 hours (Figure 3). The highest viability obtained by the maximum point of the regression curve was the 94.24% at 109.81 hours after inoculation.

Figure 3
Response of the pollen grains viability of the GBrPF accession at different times under room temperature by in vitro germination and staining with 1% acetic carmine

According to Souza, Pereira and Martins (2002)SOUZA, M. M.; PEREIRA, T. N. S.; MARTINS, E. R. Microsporogênese e microgametogênese associadas ao tamanho do botão floral e da antera e viabilidade polínica em maracujazeiro amarelo (Passiflora edulis Sims f. flavicarpa Degener). Ciência e Agrotecnologia, v. 26, p. 1209-1217, 2002., values above 70% are considered as high pollen viability; from 31 to 69% as intermediate and up to 30% as low pollen viability. The results of this study indicate intermediate and high viability values up to nine days after the extraction of pollen grains of GBrPF accession. Viability times higher than those reported by Santos et al. (1996)SANTOS, G. et al. Manual on standardized research techniques in coconut breeding. Roma: IPGRI, 1996. 45 p. indicate viability under field conditions for Cocos nucifera L. of only six days.

In the MGD coconut, Armendariz et al.(2006)ARMENDARIZ, B. H. C. et al. Pollen fertility and female flower anatomy of micropropagated coconut palms. Revista Fitotécnica Mexicana, v. 29, n. 4, p. 373-378, 2006. found that the viability obtained by tetrazolium solution showed higher values (93.4 ± 8.9%) than those obtained by in vitro germination (40.2 ± 15.6%). The authors also reported the highest variation coefficient for results obtained for viability by in vitro germination compared to tetrazolium and suggest that the in vitro germination test should be used to assess the pollen grain viability of Cocos nucifera L. Probably the variation be explained by the fact that observed the methodologies involving dyes solution weren’t efficient to estimate pollen viability evaluation, because of the deficient pollen staining, as reported by França et al. (2009)FRANÇA, L. et al. Viability of eggplant pollen. Crop Breeding & Applied Biotechnology, v. 9, n. 4, p. 320-327, 2009.. Einhardt, Correia and Raseira (2006)EINHARDT, P. M.; CORREA, E. R.; RASEIRA, M. C. B. Comparação entre métodos para testar a viabilidade de pólen de pessegueiro. Revista Brasileira Fruticultura, v. 28, n. 1, p. 5-7, 2006. worked with peach pollen grain and observed that the method used for assessing the viability of pollen grain by staining overestimates viability while the in vitro test underestimates it. This may explain the antagonism found between results obtained using both methods.

However, the efficiency of the use of dyes has been variable depending on the species and positive results have been reported for various staining techniques on different plant species (ABDELGADIR; JOHNSON; VAN STADEN, 2012ABDELGADIR, H. A.; JOHNSON, S. D.; VAN STADEN, J. Pollen viability, pollen germination and pollen tube growth in the biofuel seed crop Jatropha curcas (Euphorbiaceae). South African Journal of Botany, v. 79, p. 132-139, 2012.).

CONCLUSIONS

1. The culture medium of Lora (2006)LORA, M. A. J. et al. Low temperature storage and in vitro germination of cherimoya (Annona cherimola Mill) pollen. Scientia Horticulturae, v. 1, n. 1, p. 91-94, 2006. is suitable to assess the in vitro germination of pollen grain of the AVeBrJ and GBrPF accessions;

2. The pollen grain of the AVeBrJ accession present intermediate viability (66.87%) at room temperature up to 23.14 hours by in vitro germination;

3. The pollen grain of the GBrPF accession present high viability (above 70%) at room temperature up to 120 hours by in vitro germination.

  • Parte da Dissertação de Mestrado da primeira autora, apresentada ao Programa de Pós-Graduação em Biotecnologia em Recursos Naturais, Universidade Federal de Sergipe

ACKNOWLEDGMENTS

To Brazilian Agricultural Research Corporation (EMBRAPA), to International Coconut Genetic Resources Network (COGENT) and National Biodiversity Mainstreaming and Institutional Consolidation Project (PROBIO II) for financial support and CAPES/FAPITEC-SE for scholarship.

REFERENCES

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Publication Dates

  • Publication in this collection
    Apr-Jun 2015

History

  • Received
    25 Apr 2013
  • Accepted
    12 Jan 2015
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