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Tissue culture and biotechnological techniques applied to passion fruit with ornamental potential: an overview

Cultura de tecidos e técnicas biotecnológicas aplicadas em maracujá com potencial ornamental: uma revisão

Abstract

The ornamental flower sector has growing over the past years worldwide with potential for further expansion. Among the ornamental plants, Passiflora species have been gaining ground in the market, mainly in European and North American countries. However, the market aiming the use of these species in ornamentation is still poorly explored. The inclusion of passion flower in the list of ornamental plants is related to the peculiar characteristics of the flower as it is complex structure, capacity of flowering all year long and also by the abundance and exuberance of the leaves, which in many species adds an ornamental value. Among the biotechnological tools for the production of ornamental plants, tissue culture has been outstanding in the cloning of elite genotypes, with high phytosanitary quality and large scale production. In addition, it offers possibilities of producing new varieties with characteristics peculiar to the market of ornamental plants. The diversity of wild Passiflora opens perspectives to the conservation, market and production of ornamental Passiflora cultivars.

Keywords:
Biotechnology; hybrids; micropropagation; ornamental Passiflora; polyploids

Resumo

O setor de flores ornamentais vem crescendo ao longo dos últimos anos em todo o mundo com potencial expansao. Entre as plantas ornamentais, espécies de Passiflora vem ganhando espaço no mercado, principalmente nos países da Europa e América do Norte. Contudo, o uso destas espécies na ornamentação ainda é pouco explorado. A inclusão da flor do maracujazeiro, na lista de plantas ornamentais está relacionada às características peculiares da flor como sua estrutura complexa, capacidade de floração durante o ano todo e também pela abundância e exuberância das folhas, que em muitas espécies agrega valor ornamental. Entre as ferramentas biotecnológicas para a produção de plantas ornamentais, cultura de tecidos tem sido proeminente na clonagem de genótipos elite, com alta qualidade fitossanitária e produção em larga escala. Além disso, oferece possibilidades de produzir novas variedades com características peculiares ao mercado de plantas ornamentais. A diversidade de espécies silvestres abre perspectivas para o mercado e produção de cultivares de Passiflora ornamental.

Palavras chave:
Biotecnologia; híbridos; micropropagação; Passiflora ornamental; poliploides

Introduction

Commercial floriculture is recognized as one of the most promising segments of the contemporary agribusiness. The expansion of the flower market is mainly a consequence of the constant incorporation of new techniques and technologies of production and logistics as well as the domestication and/or introduction of new species and cultivars into the market (Junqueira and Peetz, 2017JUNQUEIRA, A.H.; PEETZ, M.S. Brazilian consumption of flowers and ornamental plants: habits, practices and trends. Ornamental Horticulture, v.23, n.2, p.178-184, 2017. https://doi:10.14295/oh.v23i2.1070
https://doi:10.14295/oh.v23i2.1070...
; Rabobank, 2016RABOBANK INDUSTRY. World Floriculture Map. 2016: Equator Countries Gathering Speed.https://research.rabobank.com/far/en/sectors/regionalfoodagri/worldfloriculturemap-2019.
https://research.rabobank.com/far/en/sec...
). Among the ornamental plant species, those of the genus Passiflora have gained prominence in the ornamental sector, especially in European and in North American countries. Although the Passiflora species are mostly native from South America, they have not been used as ornamental plants, in those countries, especially due to the low number of breeding programs for such purposes (Santos et al., 2012SANTOS, E.A.; SOUZA, M.M.; ABREU, P.P.; CONCEIÇÃO, L.D.H.C.S.; ARAÚJO, I.S.; VIANA, A.P.; ALMEIDA, A.A.F.; FREITAS, J.C.O. Confirmation and characterization of interspecific hybrids of Passiflora L. (Passifloraceae) for ornamental use. Euphytica, v.184, p.389-399, 2012. https://doi:10.1007/s10681-011-0607-7
https://doi:10.1007/s10681-011-0607-7...
).

Passiflora species are commonly used for their fruits and derivatives, medicinal plant and as a source of oils for cosmetic industry (Pacheco et al., 2016PACHECO, G.; SIMÃO, M.S.; VIANNA, M.G.; GARCIA, R.O.; VIEIRA, M.L.C.; MANSUR, E. In vitro conservation of Passiflora - a review. Scientia Horticulturae, v.211, p.305-311, 2016. https://doi:10.1016/j.scienta.2016.09.004
https://doi:10.1016/j.scienta.2016.09.00...
; Cerqueira-Silva et al., 2014CERQUEIRA-SILVA, C.B.M.; JESUS, O.N.; SANTOS, E.S.L.; CORRÊA, R.X., SOUZA, A.P. Genetic breeding and diversity of the genus Passiflora: progress and perspectives in molecular and genetic studies. International Journal of Molecular Sciences, v.15, n.8, p.14122-14152, 2014. https://doi:10.3390/ijms150814122
https://doi:10.3390/ijms150814122...
). The use of passion flowers as an ornamental plant is due their beauty and exuberance. These flowers are found in the most diverse forms, sizes, and colors and have a distinguished scent (Montero et al., 2013MONTERO, D.A.V.; MELETTI, L.M.A.M.; MARQUES, M.M.O. Fenologia do florescimento e características do perfume das flores de Passiflora quadrangularis l. (maracujá-melão). Revista Brasileira de Horticultura Ornamental, v.19, n.2, p.99-106, 2013. https://doi:10.14295/rbho.v19i2.547
https://doi:10.14295/rbho.v19i2.547...
). In the view of the recognized economic importance of the wild and commercial passion fruit species several tissue culture and biotechnological techniques have been applied to the genus (Silva et al., 2009SILVA, M.L.; PAIM PINTO, D.L.; GUERRA, M.P.; FLOH, E.I.S.; BRUCKNER, C.H.; OTONI, W.C. A novel regeneration system for wild passion fruits species (Passiflora cincinnata Mast.) based on somatic embryogenesis from mature zygotic embryos. Plant Cell Tissue and Organ Culture, v. 99, n.1, p.47-54, 2009. https://doi:10.1007/s11240-009-9574-2
https://doi:10.1007/s11240-009-9574-2...
; Otoni et al., 2013OTONI, W.C.; PINTO, D.P.L.; ROCHA, D.I.; VIEIRA, L.M.; DIAS, L.L.C.; SILVA, M.L.; SILVA, C.V.E.; LANI, R.G.; SILVA, L.C.; TANAKA, F.A.O. Organogenesis and somatic embryogenesis in passionfruit (Passiflora spp.). In: ASLAM, J.; SRIVASTAVA, O.S.; SHARMA, M.P. (eds). Somatic embryogenesis and gene expression. Narosa Publishing House, New Delhi, 2013. p.1-17; Ozarowski and Thiem 2013OZAROWSKI, M.; THIEM, B. Progress in micropropagation of Passiflora spp. produce medicinal plants: a mini-review. Revista Brasileira de Farmacologia, v.23, n.6, p.937-947, 2013. https://doi:10.1590/S0102-695X2013000600011
https://doi:10.1590/S0102-695X2013000600...
; Pacheco et al., 2016PACHECO, G.; SIMÃO, M.S.; VIANNA, M.G.; GARCIA, R.O.; VIEIRA, M.L.C.; MANSUR, E. In vitro conservation of Passiflora - a review. Scientia Horticulturae, v.211, p.305-311, 2016. https://doi:10.1016/j.scienta.2016.09.004
https://doi:10.1016/j.scienta.2016.09.00...
; Carvalho et al., 2017CARVALHO, P.P.; ANTONIAZZI, C.A.; SILVA, N.T.; MIKOVSKI, A.I.; CARVALHO, I.F.; CARVALHO, M.L.S. Regeneração in vitro de Passiflora miniata Mast. Ornamental Horticulture, v.23, n.1, p.88-95, 2017. https://doi:10.14295/oh.v23i1.965.
https://doi:10.14295/oh.v23i1.965...
; Faria et al., 2018FARIA, R.B.; CARVALHO, I.F.; ROSSI, A.B.; MATOS, E.M.; ROCHA, D.I.; PAIM PINTO, D.L.; OTONI, W.C.; SILVA, M.L. High responsiveness in de novo shoot organogenesis induction of Passiflora cristalina (Passifloraceae), a wild Amazonian passion fruit species. In Vitro Cell & Development Biology - Plant, v.54, n.2, p.166-174, 2018. https://doi:10.1007/s11627017-9881y.
https://doi:10.1007/s11627017-9881y...
). The present review proposes to summarize the results achieved thus far in the biotechnology of wild Passiflora species with ornamental potential.

The ornamentation potential of passion flowers

The inclusion of passion flowers in the list of ornamental plants is related to the highly morphological complexity observed in the reproductive organs of these species. Further, some of these species flourish all year long and have a vigorous and exuberant vegetative growth, with leaves of diverse morphologies, which adds ornamental value to it (Abreu et al., 2009ABREU P.P.; SOUZA M.M.; SANTOS E.A.; PIRES M.V.; PIRES M.M.; ALMEIDA A.A.F. Passion flower hybrids an their use in the ornamental plant market: perspectives for sustainable development with emphasis on Brazil. Euphytica, v.166, n.3, p.307-315, 2009. https://doi:10.1007/s10681-008-9835-x.
https://doi:10.1007/s10681-008-9835-x...
; Meletti et al., 2011MELETTI, L.M.M.; SOARES-SCOTT, M.D.; BERNACCI, L.C.; ALVES, V.; AZEVEDO FILHO, J.A. Caracterização de Passiflora mucronata Lam.: nova alternativa de maracujá. Revista Brasileira de Horticultura Ornamental, v.17, n.2, p.87-95, 2011. https://doi:10.14295/rbho.v17i1.721
https://doi:10.14295/rbho.v17i1.721...
; Faleiro et al., 2017FALEIRO, F.G.; JUNQUEIRA, N.T.V.; JESUS, O.N.; COSTA, A.M.; MACHADO, C.F.; JUNQUEIRA, K.P. ARAÚJO, F.P.; JUNGHANS, T. Espécies de maracujazeiro no mercado internacional. In: JUNGHANS, T., JESUS, O.N. (eds.) Maracujá: do cultivo à comercialização. Embrapa, Brasília, 2017. p.15-37.). The use of Passiflora as ornamental plants started in the 15th century and continues to this day in the market of hybrid plants, especially in Europe and in the North American countries. Over 400 hybrids for ornamental purposes have been registered across the world (Vanderplank, 2000VANDERPLANK, J. Passion flowers. Cambridge: The MIT Press, 2000.).

Passifloraceae has a pantropical distribution, with approximately 630 species, and great diversification in terms of leaf, fruit, and flower characteristics (Ocampo et al., 2007OCAMPO, J.P.; COPPENS, D.'; EECKENBRUGG, E.G.; RESTREPO, M.; JARVIS, A.; SALAZAR, M.; CAETANO, C. Diversity of colombian Passifloraceae: biogeography and an updated list for conservation. Biota Colombiana, v.8, n.1, 1-45, 2007. https://doi:10.21068/bc.v8i1.181
https://doi:10.21068/bc.v8i1.181...
; Souza and Hopkins, 2011SOUZA, M.A.D.; HOPKINS, M.J.G. Passiflora fissurosa, uma nova espécie de Passifloraceae para o Amazonas, Brasil. Acta Amazônica, v.41, p.449-442, 2011. https://doi:10.1590/S0044-59672011000400002
https://doi:10.1590/S0044-59672011000400...
). The genus Passiflora comprises approximately 530 species (Ulmer and Macdougal, 2004ULMER, T.; MACDOUGAL, J.M. Passiflora: passionflowers of the world. Portland: Timber Press, 2004), 150 to 200 of which originate in Brazil and can be used for multiple purposes such as food, medicine, cosmetics, or ornamentation (Abreu et al., 2009ABREU P.P.; SOUZA M.M.; SANTOS E.A.; PIRES M.V.; PIRES M.M.; ALMEIDA A.A.F. Passion flower hybrids an their use in the ornamental plant market: perspectives for sustainable development with emphasis on Brazil. Euphytica, v.166, n.3, p.307-315, 2009. https://doi:10.1007/s10681-008-9835-x.
https://doi:10.1007/s10681-008-9835-x...
; Pipino et al., 2010PIPINO, L.; BRAGLIA, L.; GIOVANNINI, A.; FASCELLA, G.; MERCURI, A. In vitro regeneration and multiplication of Passiflora hybrid “Guglielmo Betto”. In: JAIN, S.M.; OCHATT, S.J. (eds.). Protocols for in vitro propagation of ornamental plants, methods in molecular biology. Estados Unidos: Humana Press, 2010. https://doi:10.1007/978-1-60327-114-1_15 p. 153-162.
https://doi:10.1007/978-1-60327-114-1_15...
). The genus Passiflora is divided into four subgenera: Decaloba, Astrophea, Deidamioides, and Passiflora. The species of greatest importance belong to the subgenus Passiflora (Ulmer and Macdougal, 2004ULMER, T.; MACDOUGAL, J.M. Passiflora: passionflowers of the world. Portland: Timber Press, 2004). Passiflora flowers are pentamerous, bisexual, and actinomorphic, with a distinct perianth presenting sepals and petals of different shapes and sizes. The petals are usually membranous and develop on the border of the calix tube. All Passiflora flowers have an androgynophore that elevates the five fused stamens up to the base and which are also united with a gynoecium composed of three fused carpels (Vanderplank, 2000VANDERPLANK, J. Passion flowers. Cambridge: The MIT Press, 2000.; Ulmer and Macdougal, 2004ULMER, T.; MACDOUGAL, J.M. Passiflora: passionflowers of the world. Portland: Timber Press, 2004; Abreu et al., 2009ABREU P.P.; SOUZA M.M.; SANTOS E.A.; PIRES M.V.; PIRES M.M.; ALMEIDA A.A.F. Passion flower hybrids an their use in the ornamental plant market: perspectives for sustainable development with emphasis on Brazil. Euphytica, v.166, n.3, p.307-315, 2009. https://doi:10.1007/s10681-008-9835-x.
https://doi:10.1007/s10681-008-9835-x...
; Scorza et al., 2017SCORZA, L.C.T.; HERNANDES-LOPES, J.; MELO-DEPINHA, G.F.A.; DORNELAS, M.C. Expression patterns of Passiflora edulis APETALA1/FRUITFULL homologues shed light onto tendril and corona identities. EvoDevo, v.8, n.3, p.3, 2017. https://doi:10.1186/s13227-017-0066-x
https://doi:10.1186/s13227-017-0066-x...
) (Figure 1).

Figure 1
Floral structure of the wild passion flower of Passiflora capparidifolia.

Passiflora flowers are considered exotic because of the presence of a multiple series of corona filaments observed between the petals and the androgynophore column. The corona is a distinctive feature of the genus Passiflora, and the diversity of shapes, sizes and colors of these filaments seems to be related to the different pollinating systems observed in the genus (Aizza and Dornelas, 2011AIZZA, L.C.B.; DORNELAS, M.C. A genomic approach to study anthocyanin synthesis and flower pigmentation in passionflowers. Journal of Nucleic Acids, v.2011, n.8, p.1-17, 2011. https://:10.4061/2011/371517.
https://:10.4061/2011/371517...
). Sporophytic self-incompatibility is another important feature of the floral biology of Passiflora, which determines allogamy. This characteristic contributes to the increased genetic variability, which may favor the use of those species as ornamental plants (Bruckner et al., 1995BRUCKNER, C.H.; CASALI, V.W.D.; MORAES, C.F.; REDAZZI, A.J.; SILVA, E.A.M. Self-incompatibility in passion fruit (Passiflora edulis Sims). Acta Horticulturae, v.370, n. 7, p.45-57, 1995. https://doi:10.17660/ActaHortic.1995.370.7.
https://doi:10.17660/ActaHortic.1995.370...
; Ferreira et al., 2010FERREIRA, T.G.T.; PENHA, H.A.; ZUCCHI, M.I.; SANTOS, A.A; HANAI, L.R.N.; JUNQUEIRA, N.; BRAGA, M.F.; VENCOVSKY, R.; VIEIRA, M.L.C. Outcrossing rate in sweet passion fruit based on molecular markers. Plant Breeding, v.129, n.6, p.727-730, 2010. https://doi:10.1111/j.1439-0523.2009.01744.x.
https://doi:10.1111/j.1439-0523.2009.017...
).

Several wild Passiflora spp. are already described as ornamental plant such as; Passiflora alata (Figure 2A), Passiflora setacea (Oliveira and Ruggiero, 2005OLIVEIRA, J.C.; RUGGIERO, C. Espécies de maracujá com potencial agronômico. p. 143-158. In: Faleiro FG, Junqueira NTV, Braga MF. (Ed.). Maracujá: germoplasma e melhoramento genético. Planaltina Distrito Federal: Embrapa Cerrados, 2005.), Passiflora amethystina, Passiflora actinia, Passiflora triloba Ruiz & Pav. EX DC (Peixoto, 2005PEIXOTO, M. Problemas e perspectivas do maracujá ornamental. In: FALEIRO, F.G.; JUNQUEIRA, N.T.V.; BRAGA, M.F. Maracujá: germoplasma e melhoramento genético. Planaltina: Embrapa Cerrados, 2005. p.457-463.), Passiflora caerulea (Conceição et al., 2011CONCEIÇÃO, L.D.H.C.S.; SOUZA, M.M.; BELO, G.O.; SANTOS, S.F.; FREITAS, J.C.O. Hybridization among wild passionflower species. Revista Brasileira de Botânica, v.34, n.6, p.237-240, 2011. https://doi:10.1590/S0100-84042011000200011.
https://doi:10.1590/S0100-84042011000200...
), Passiflora cincinnata (Figure 2B) (Oliveira and Ruggiero, 2005OLIVEIRA, J.C.; RUGGIERO, C. Espécies de maracujá com potencial agronômico. p. 143-158. In: Faleiro FG, Junqueira NTV, Braga MF. (Ed.). Maracujá: germoplasma e melhoramento genético. Planaltina Distrito Federal: Embrapa Cerrados, 2005.); Passiflora mucronata (Meletti et al., 2011MELETTI, L.M.M.; SOARES-SCOTT, M.D.; BERNACCI, L.C.; ALVES, V.; AZEVEDO FILHO, J.A. Caracterização de Passiflora mucronata Lam.: nova alternativa de maracujá. Revista Brasileira de Horticultura Ornamental, v.17, n.2, p.87-95, 2011. https://doi:10.14295/rbho.v17i1.721
https://doi:10.14295/rbho.v17i1.721...
), Passiflora morifolia, Passiflora suberosa litoralis, Passiflora palmeri var. sublanceolata (Pires et al., 2012PIRES, M.V.; ALMEIDA, A.A.F.; FIGUEIREDO, A.L.; GOMES, F.P.; SOUZA, M.M. Germination and seedling growth of ornamental species of Passiflora under artificial shade. Acta Scientiarum Agronomy, v.34, n.1, p.67-75, 2012. https://doi:10.4025/actasciagron.v34i1.11623
https://doi:10.4025/actasciagron.v34i1.1...
), Passiflora capsularis, Passiflora rubra (Amorim et al., 2011AMORIM, J.S.; SOUZA, M.M.; VIANA, A.J.C.; FREITAS, J.C.O. Self cross and interspecific pollinations in Passiflora capsularis and P. rubra. Revista Brasileira de Botânica, v.34, n.4 p.537-544, 2011. https://doi:10.1590/S0100-84042011000400007.
https://doi:10.1590/S0100-84042011000400...
). Other species stand out for the beauty and exuberance of their flowers showing a great ornamental potential to be explored, such as; Passiflora nitida (Figure 2C), Passiflora capparidifolia (Figure 2D), Passiflora miniata (Figure 2E) Passiflora cristalina (Figure 2F).

Figure 2
Flowers of species of Passiflora with ornamental potential. (A) P. alata; (B) P. cincinnata; (C) P. nitida; (D) P. capparidifolia; (E) P. miniata; (F) P. cristalina.

Passiflora hybrids for ornamental purposes

In view of the ornamental potential of wild Passiflora, research centers have selected species with adequate morphological and adaptive traits for the generation of ornamental hybrids (Cerqueira-Silva et al., 2014CERQUEIRA-SILVA, C.B.M.; JESUS, O.N.; SANTOS, E.S.L.; CORRÊA, R.X., SOUZA, A.P. Genetic breeding and diversity of the genus Passiflora: progress and perspectives in molecular and genetic studies. International Journal of Molecular Sciences, v.15, n.8, p.14122-14152, 2014. https://doi:10.3390/ijms150814122
https://doi:10.3390/ijms150814122...
). The first Passiflora hybrid developed for ornamental purposes was reported in 1819 by English breeder Thomas Milne, who made a cross between P. caerulea and P. racemosa and obtained the sexual hybrid named ‘P. violacea’ (Vanderplank, 2000VANDERPLANK, J. Passion flowers. Cambridge: The MIT Press, 2000.). Currently, passion flower hybryds; e.g. Passiflora ‘Albo-nigra’, P. ‘Amethyst’, P. ‘Star of Bristol’, and P. ‘Star of Kingston’ obtained P. alata and P. caerulea have been used for decoration of European and American greenhouses (Ulmer and Macdougal, 2004ULMER, T.; MACDOUGAL, J.M. Passiflora: passionflowers of the world. Portland: Timber Press, 2004; Conceição et al., 2011CONCEIÇÃO, L.D.H.C.S.; SOUZA, M.M.; BELO, G.O.; SANTOS, S.F.; FREITAS, J.C.O. Hybridization among wild passionflower species. Revista Brasileira de Botânica, v.34, n.6, p.237-240, 2011. https://doi:10.1590/S0100-84042011000200011.
https://doi:10.1590/S0100-84042011000200...
).

In Brazil, the Brazilian Agricultural Research Corporation (Embrapa) developed three Passiflora hybrids for ornamental use. The first hybrid developed was ‘BRS Estrela do Cerrado’, obtained from the cross between the wild species P. coccinea Aubl. (red flowers), and P. setacea DC. (white flowers). Later, another two hybrids were produced from the backcross between ‘BRS Estrela do Cerrado’ and the parental species, namely ‘BRS Roseflora’, obtained from the backcross between ‘BRS Estrela do Cerrado’ and P. setacea; and ‘BRS Rubiflora’, obtained from the backcross between ‘BRS Estrela do Cerrado’ and P. coccinea (Faleiro et al., 2009FALEIRO, F.G.; JUNQUEIRA, N.T.N.V.; BRAGA, M.F.; PEIXOTO, J.R.; BORGES, R.S.; ARAÚJO, S.C.B.; ANDRADE, S.E.M.; COSTA, A.M.; CASTELLEN, M.S.; VAZ, A.P.A.; SOARES-SCOTT, M.D.; BERNACCI, L.C.; ANDRADE, G.A. BRS Estrela do Cerrado, BRS Rubiflora e BRS Roseflora: híbridos de maracujazeiro para uso como plantas ornamentais. In: FALEIRO, F.G.; FARIAS NETO, A.L.; RIBEIRO JUNIOR, W.Q. (eds) Livros e Cultivares Apresentados no II Encontro da Sociedade Brasileira de Melhoramento de Plantas - Regional - DF. Embrapa Cerrados, Planaltina-DF, 2009. p.45.). The hybrids released by Embrapa and partners have exuberant flowers and are indicated for landscaping of large areas such as walls, fences, and pergolas. In 2016, Embrapa released two new hybrid cultivars for landscaping of large areas. Hybrid ‘BRS Céu do Cerrado’, with bluish flowers, derived from the cross between the species P. incarnata and P. edulis; and ‘BRS Rosea Púrpura’, with pinkish flowers, originating from the triple cross P. incarnata × P. quadrifaria × P. setacea (Fonseca et al., 2017FONSECA, K.G.; FALEIRO, F.G.; JUNQUEIRA, N.T.V.; BARTH, M.; FELBERG, N.P. Morphoagronomic and molecular characterization of ornamental passion fruit cultivars. Pesquisa Agropecuária Brasileira, v.52, n.10, p.849-860, 2017. https://doi:10.1590/s0100-204x2017001000004
https://doi:10.1590/s0100-204x2017001000...
). Other Brazilian institutions also produced hybrids for ornamental purposes; e.g. ‘Passiflora alva’, ‘Passiflora priscilla’, and ‘Passiflora aninha’, developed by the State University of Santa Cruz, Brazil, from the cross between P. palmeri and P. foetida (Cerqueira-Silva et al., 2014CERQUEIRA-SILVA, C.B.M.; JESUS, O.N.; SANTOS, E.S.L.; CORRÊA, R.X., SOUZA, A.P. Genetic breeding and diversity of the genus Passiflora: progress and perspectives in molecular and genetic studies. International Journal of Molecular Sciences, v.15, n.8, p.14122-14152, 2014. https://doi:10.3390/ijms150814122
https://doi:10.3390/ijms150814122...
). Fonseca et al. (2017)FONSECA, K.G.; FALEIRO, F.G.; JUNQUEIRA, N.T.V.; BARTH, M.; FELBERG, N.P. Morphoagronomic and molecular characterization of ornamental passion fruit cultivars. Pesquisa Agropecuária Brasileira, v.52, n.10, p.849-860, 2017. https://doi:10.1590/s0100-204x2017001000004
https://doi:10.1590/s0100-204x2017001000...
recently validated morpho-agronomic descriptors used in the protection of cultivars in Brazil and the molecular characterization of ornamental Passiflora hybrids developed by Embrapa aiming to differentiate these cultivars obtained from crosses between wild species.

Micropropagation of wild Passiflora spp. with ornamental potential

Micropropagation studies in Passiflora started in 1966 (Nakayama, 1966NAKAYAMA, F. Cultivo in vitro de tejidos de Passiflora caerulea. Revista de la Facultad de Agronomia de la Universidad Nacional de La Plata, v.42, p.63-74, 1966.) from the culture of nodal segments of an important ornamental species, P. caerulea. Since then, a growing number of studies describing in vitro techniques applied to the genus have been published for commercial and wild species with ornamental and phamaceutic propreties (Drew, 1997DREW, R.A. Micropropagation of Passiflora species (Passionfruit). In: BAJAJ YPS. (ed.) Biotechnology in agriculture and forestry. High-tech and micropropagation. Springer Verlag, Berlin, 1997. p.135-149. https://doi:10.1007/978-3-662-07774-0_9
https://doi:10.1007/978-3-662-07774-0_9...
; Otoni et al., 2013OTONI, W.C.; PINTO, D.P.L.; ROCHA, D.I.; VIEIRA, L.M.; DIAS, L.L.C.; SILVA, M.L.; SILVA, C.V.E.; LANI, R.G.; SILVA, L.C.; TANAKA, F.A.O. Organogenesis and somatic embryogenesis in passionfruit (Passiflora spp.). In: ASLAM, J.; SRIVASTAVA, O.S.; SHARMA, M.P. (eds). Somatic embryogenesis and gene expression. Narosa Publishing House, New Delhi, 2013. p.1-17; Ozarowski and Thiem, 2013OZAROWSKI, M.; THIEM, B. Progress in micropropagation of Passiflora spp. produce medicinal plants: a mini-review. Revista Brasileira de Farmacologia, v.23, n.6, p.937-947, 2013. https://doi:10.1590/S0102-695X2013000600011
https://doi:10.1590/S0102-695X2013000600...
; Rathod et al., 2014RATHOD, H.P.; POHARE, M.B.; BHOR, S.; JADHAV, K.P.; BATULE, B.S.; SHAHAKAR, S.B.; WAGH, S.; WADEKAR, H.B.; KELATKAR, S.K.; KULKARNI, M.R. In vitro micro propagation of Blue Passion Flower (Passiflora caerulea L.). Trends in Bioscience, v.7, n.19, p.3079-3082, 2014.; Pacheco et al., 2016PACHECO, G.; SIMÃO, M.S.; VIANNA, M.G.; GARCIA, R.O.; VIEIRA, M.L.C.; MANSUR, E. In vitro conservation of Passiflora - a review. Scientia Horticulturae, v.211, p.305-311, 2016. https://doi:10.1016/j.scienta.2016.09.004
https://doi:10.1016/j.scienta.2016.09.00...
; Rocha et al., 2018ROCHA, D.I.; VIEIRA, L.M.; KOEHLER, A.D.; OTONI, W.C. Cellular and morpho-histological foundations of in vitro plant regeneration. In: LOYOLA-VARGAS, V.M.; OCHOA-ALEJO, N. (Eds.) Plant Cell Culture Protocols, Methods in Moleular Biology, v.1815, Springer, New York, 2018. https://doi:10.1007/978-1-4939-8594-4_3 p.47-68.
https://doi:10.1007/978-1-4939-8594-4_3...
; Vieira et al., 2018VIEIRA, L.M.; SILVA, P.O.; FERNANDES, A.M.; ROCHA, D.I.; OTONI, W.C. Protocol for somatic embryogenesis in Passiflora cincinnata Mast. (Passifloraceae). In: JAIN M.S.; GUPTA, P. (Eds.) Stepwise protocols for somatic embryogenesis of woody plants. 2ed, Springer International Publishing AG, Cham, 2018. p.253-265. https://doi:10.1007/978-3-319-79087-9_21
https://doi:10.1007/978-3-319-79087-9_21...
).

Among the micropropagation systems established for Passiflora, organogenesis is the main morphogenetic pathway of regeneration (Otoni et al., 2013OTONI, W.C.; PINTO, D.P.L.; ROCHA, D.I.; VIEIRA, L.M.; DIAS, L.L.C.; SILVA, M.L.; SILVA, C.V.E.; LANI, R.G.; SILVA, L.C.; TANAKA, F.A.O. Organogenesis and somatic embryogenesis in passionfruit (Passiflora spp.). In: ASLAM, J.; SRIVASTAVA, O.S.; SHARMA, M.P. (eds). Somatic embryogenesis and gene expression. Narosa Publishing House, New Delhi, 2013. p.1-17) (Table 1), although recent research has demonstrated the occurrence of regeneration via embryogenesis (Silva et al., 2009SILVA, M.L.; PAIM PINTO, D.L.; GUERRA, M.P.; FLOH, E.I.S.; BRUCKNER, C.H.; OTONI, W.C. A novel regeneration system for wild passion fruits species (Passiflora cincinnata Mast.) based on somatic embryogenesis from mature zygotic embryos. Plant Cell Tissue and Organ Culture, v. 99, n.1, p.47-54, 2009. https://doi:10.1007/s11240-009-9574-2
https://doi:10.1007/s11240-009-9574-2...
, 2015SILVA, M.L.; PAIM PINTO, D.L.; GUERRA, M.P.; LANI, E.R.G.; CARVALHO, I.F.; ROSSI, A.A.B.; OTONI, W.C. Produção de sementes sintéticas de maracujazeiro silvestre com potencial ornamental. Ornamental Horticulture, v.21, n.3, p.331-338, 2015. https://doi:10.14295/oh.v21i3.752
https://doi:10.14295/oh.v21i3.752...
; Paim Pinto et al., 2011PAIM PINTO, D.L.; ALMEIDA, A.M.R.; RÊGO, M.M.; SILVA, M.L.; OLIVEIRA, E.J.; OTONI, W.C. Somatic embryogenesis from mature zygotic embryos of commercial passionfruit (Passiflora edulis Sims) genotypes. Plant Cell Tissue and Organ Culture, v.107, n.3, p.521-530, 2011. https://doi:10.1007/s11240-011-0003-y
https://doi:10.1007/s11240-011-0003-y...
; Rosa et al., 2015ROSA, Y.B.C.J.; BELLO, C.C.M.; DORNELAS, M.C. Species-dependent divergent responses to in vitro somatic embryo induction in Passiflora spp. Plant Cell Tissue and Organ Culture, v.20, p.69-77, 2015. https://doi:10.1007/s11240-014-0580-7
https://doi:10.1007/s11240-014-0580-7...
; Ferreira et al., 2015FERREIRA, D.A.T; SATTLER, M.C.; CARVALHO, C.R.; CLARINDO, W.R. Embryogenic potential of immature zygotic embryos of Passiflora: a new advance for in vitro propagation without plant growth regulators. Plant Cell Tissue and Organ Culture, v.122, n.3, p.629-638, 2015. https://doi:10.1007/s11240-015-0796-1
https://doi:10.1007/s11240-015-0796-1...
). With only a few exceptions (Moran Robles, 1978MORAN ROBLES, M.J. In vitro vegetative multiplication of axillary buds of P. edulis var. flavicarpa Degener and P. mollissima Bairley. Fruits, v.33, p.701-715, 1978.), the MS growth medium (Murashige and Skoog, 1962MURASHIGE T.; SKOOG, F. A revised medium for rapid growth and bioassays with tobacco tissue cultures. Physiology Plant, v.15, p.473-497, 1962. https://doi:10.1111/j.1399-3054.1962.tb08052.x
https://doi:10.1111/j.1399-3054.1962.tb0...
) has been used. However, supplementation with growth regulators varies according to the morphogenetic pathway to be induced. For in vitro organogenesis induction, 6-benzyladenine (BA) at concentration range from 2.2 to 8.8 μM have been adopted for passion fruit shoot bud induction, although thidiazuron (1.1-2.3 μM) alone or in combination with BA has also been reported (Trevisan and Mendes, 2005TREVISAN, F.; MENDES, B.M.J. Optimization of in vitro organogenesis in passion fruit (Passiflora edulis f. flavicarpa). Scientia Agricola, v.2, n.4, p.346-350, 2005. https://doi:10.1590/S0103-90162005000400007
https://doi:10.1590/S0103-90162005000400...
; Pinto et al., 2010PINTO, A.P.C.; MONTEIRO-HARA, A.C.A.; STIPP, L.C.L.; MENDES, B.M.J. In vitro organogenesis of Passiflora alata. In Vitro Cellular & Developmental Biology-Plant, v.46, n.1, p.28-33. https://doi:10.1007/s11627-009-9251-5, 2010.
https://doi:10.1007/s11627-009-9251-5...
; Garcia et al., 2011GARCIA, R.O.; PACHECO, G.; FALCÃO, E.; BORGES, G.; MANSUR, E. Influence of type of explant plant growth regulators, salt composition of basal medium, and light on callogenesis and regeneration on Passiflora suberosa L. (Passifloraceae). Plant Cell Tissue and Organ Culture, v.106, p.47-54, 2011. https://doi:10.1007/s11240-010-9892-4
https://doi:10.1007/s11240-010-9892-4...
; Vieira et al., 2014VIEIRA, LM.; ROCHA, D.I.; TAQUETTI, M.F.; SILVA, L.C.; CAMPOS, J.M.S.; VICCINI L.F.; OTONI, W.C. In vitro plant regeneration of Passiflora setacea D.C. (Passifloraceae): the influence of explant type, growth regulators, and incubation conditions. In Vitro Cellular & Developmental Biology-Plant, v.50, n.6, p.738-745, 2014. https://doi:10.1007/s11627-014-9650-0
https://doi:10.1007/s11627-014-9650-0...
). On the other hand, somatic embryogenesis has been optimized for several Passiflora species from mature and immature zygotic embryos in media supplemented with different combinations of 2,4-D (8.8-72.4 μM) and 4.5 μM BA (Table 1).

Table 1
In vitro regeneration systems for Passiflora species with ornamental potential.

Among the ornamental passion flowers, Passiflora cincinnata has showing an excellent in vitro performance thanks to its high regenerant formation frequency (Lombardi et al., 2007LOMBARDI, S.P.; PASSOS, I.R.S.; NOGUEIRA, M.C.S.; APPEZZATO-DA-GLÓRIA, B. In vitro regeneration from roots and leaf discs of Passiflora cincinnata Mast. Brazilian Archives of Biology and Technology, v.50, n.2, p.239-247, 2007. https://doi:10.1590/S1516-89132007000200009
https://doi:10.1590/S1516-89132007000200...
; Silva et al., 2009SILVA, M.L.; PAIM PINTO, D.L.; GUERRA, M.P.; FLOH, E.I.S.; BRUCKNER, C.H.; OTONI, W.C. A novel regeneration system for wild passion fruits species (Passiflora cincinnata Mast.) based on somatic embryogenesis from mature zygotic embryos. Plant Cell Tissue and Organ Culture, v. 99, n.1, p.47-54, 2009. https://doi:10.1007/s11240-009-9574-2
https://doi:10.1007/s11240-009-9574-2...
; Dias et al., 2009DIAS, L.L.C.; SANTA-CATARINA, C.; RIBEIRO, D.M.; BARROS, R.S.; FLOH, E.I.S.; OTONI, W.C. Ethylene and polyamine production patterns during in vitro shoot organogenesis of two passion fruit species as affected by polyamines and their inhibitor. Plant Cell Tissue and Organ Culture, v.99, n.2, p.199-208, 2009. https://doi:10.1007/s11240-009-9594-y.
https://doi:10.1007/s11240-009-9594-y...
; Silva et al., 2011SILVA, C.V.; OLIVEIRA, L.S.; LORIATO, V.A.P; SILVA, L.C.; CAMPOS, J.M.S; VICCINI, L.F.; OLIVEIRA, E.J.; OTONI, W.C. Organogenesis from root explants of commercial populations of Passiflora edulis Sims and a wild passionfruit species, P. cincinnata Masters. Plant Cell Tissue and Organ Culture, v.107, n.3, p.407-416, 2011. https://doi:10.1007/s11240-011-9991-x
https://doi:10.1007/s11240-011-9991-x...
, Faleiro et al., 2019FALEIRO, F.G.; JUNQUEIRA, N.T.V.; JUNGHANS T.G.; JESUS, O.N.; MIRANDA, D.; OTONI, W.C. Advances in passion fruit (Passiflora spp.) propagation. Revista Brasileira de Fruticultura, v. 41, n. 2, 2019. doi: http://dx.doi.org/10.1590/0100-29452019155
http://dx.doi.org/10.1590/0100-294520191...
). Somatic embryogenesis systems have been established for this species from root explants (Reis et al., 2003REIS, L.B.; PAIVA NETO, V.B.P.; PICOLI, E.A.T.; COSTA, M.G.C.; RÊGO, M.M.; CARVALHO, C.R.; FINGER, F.L.; OTONI, W.C. Axillary bud development of passionfruit as affected by ethylene precursor and inhibitors. In Vitro Cellular & Developmental Biology-Plant, v.39, n.6, p.618-622, 2003. https://doi:10.1079/IVP2003455
https://doi:10.1079/IVP2003455...
) and mature zygotic embryos (Silva et al., 2009SILVA, M.L.; PAIM PINTO, D.L.; GUERRA, M.P.; FLOH, E.I.S.; BRUCKNER, C.H.; OTONI, W.C. A novel regeneration system for wild passion fruits species (Passiflora cincinnata Mast.) based on somatic embryogenesis from mature zygotic embryos. Plant Cell Tissue and Organ Culture, v. 99, n.1, p.47-54, 2009. https://doi:10.1007/s11240-009-9574-2
https://doi:10.1007/s11240-009-9574-2...
). However, only with zygotic embryos a reproducible protocol for somatic embryogenesis was obtained (Silva et al., 2009SILVA, M.L.; PAIM PINTO, D.L.; GUERRA, M.P.; FLOH, E.I.S.; BRUCKNER, C.H.; OTONI, W.C. A novel regeneration system for wild passion fruits species (Passiflora cincinnata Mast.) based on somatic embryogenesis from mature zygotic embryos. Plant Cell Tissue and Organ Culture, v. 99, n.1, p.47-54, 2009. https://doi:10.1007/s11240-009-9574-2
https://doi:10.1007/s11240-009-9574-2...
). For P. cincinnata, somatic embryogenesis was induced from zygotic embryos cultured in medium supplemented with a high auxin/cytokinin balance (18.1 μM 2,4-D and 4.5 μM BA). Based on this system, other authors have reported successful induction of somatic embryos for other ornamental Passiflora species, such as P. miniata (Ferreira et al., 2015FERREIRA, D.A.T; SATTLER, M.C.; CARVALHO, C.R.; CLARINDO, W.R. Embryogenic potential of immature zygotic embryos of Passiflora: a new advance for in vitro propagation without plant growth regulators. Plant Cell Tissue and Organ Culture, v.122, n.3, p.629-638, 2015. https://doi:10.1007/s11240-015-0796-1
https://doi:10.1007/s11240-015-0796-1...
), P. alata, and P. crenata (Rosa et al., 2015ROSA, Y.B.C.J.; BELLO, C.C.M.; DORNELAS, M.C. Species-dependent divergent responses to in vitro somatic embryo induction in Passiflora spp. Plant Cell Tissue and Organ Culture, v.20, p.69-77, 2015. https://doi:10.1007/s11240-014-0580-7
https://doi:10.1007/s11240-014-0580-7...
). However, for P. suberosa, only adventitious bud formation was observed when zygotic embryos were cultured in the same conditions established for P. cincinnata (Rosa et al., 2015ROSA, Y.B.C.J.; BELLO, C.C.M.; DORNELAS, M.C. Species-dependent divergent responses to in vitro somatic embryo induction in Passiflora spp. Plant Cell Tissue and Organ Culture, v.20, p.69-77, 2015. https://doi:10.1007/s11240-014-0580-7
https://doi:10.1007/s11240-014-0580-7...
). In vitro regeneration of P. suberosa was achieved from nodal segments in the presence of α-naphthaleneacetic acid (NAA), picloram, and 2,4-dichlorophenoxyacetic acid (Garcia et al., 2011GARCIA, R.O.; PACHECO, G.; FALCÃO, E.; BORGES, G.; MANSUR, E. Influence of type of explant plant growth regulators, salt composition of basal medium, and light on callogenesis and regeneration on Passiflora suberosa L. (Passifloraceae). Plant Cell Tissue and Organ Culture, v.106, p.47-54, 2011. https://doi:10.1007/s11240-010-9892-4
https://doi:10.1007/s11240-010-9892-4...
), and also from internode (Garcia et al., 2011GARCIA, R.O.; PACHECO, G.; FALCÃO, E.; BORGES, G.; MANSUR, E. Influence of type of explant plant growth regulators, salt composition of basal medium, and light on callogenesis and regeneration on Passiflora suberosa L. (Passifloraceae). Plant Cell Tissue and Organ Culture, v.106, p.47-54, 2011. https://doi:10.1007/s11240-010-9892-4
https://doi:10.1007/s11240-010-9892-4...
) and root (Rosa et al., 2016ROSA, Y.B.C.J.; MONTE-BELLO, C.C.; DORNELAS, M.C. In vitro organogenesis and efficient plant regeneration from root explants of Passiflora suberosa L. (Passifloraceae). In Vitro Cell & Development Biology-Plant, v.52, p.64-71, 2016. https://doi:10.1007/s11627-016-9747-8
https://doi:10.1007/s11627-016-9747-8...
) segments cultured in the presence of BA.

For Passiflora miniata, an Amazonian species with great ornamental potential, a regeneration system was observed via organogenesis from zygotic embryos. Regeneration occurred directly and/or from calluses, mainly in the presence of 3.32 μM BA, with an average of 40.0 shoots per explant (Carvalho et al., 2017CARVALHO, P.P.; ANTONIAZZI, C.A.; SILVA, N.T.; MIKOVSKI, A.I.; CARVALHO, I.F.; CARVALHO, M.L.S. Regeneração in vitro de Passiflora miniata Mast. Ornamental Horticulture, v.23, n.1, p.88-95, 2017. https://doi:10.14295/oh.v23i1.965.
https://doi:10.14295/oh.v23i1.965...
). Recently, Faria and collaborators (2018)FARIA, R.B.; CARVALHO, I.F.; ROSSI, A.B.; MATOS, E.M.; ROCHA, D.I.; PAIM PINTO, D.L.; OTONI, W.C.; SILVA, M.L. High responsiveness in de novo shoot organogenesis induction of Passiflora cristalina (Passifloraceae), a wild Amazonian passion fruit species. In Vitro Cell & Development Biology - Plant, v.54, n.2, p.166-174, 2018. https://doi:10.1007/s11627017-9881y.
https://doi:10.1007/s11627017-9881y...
highlighted the high responsiveness of Passiflora cristalina, another Amazonian species with ornamental potential. According to the authors, the highest mean number of shoots was observed in hypocotyl segments and in zygotic embryos when cultured in MS medium supplemented with 4.43 μM BA.

Polyploid production of ornamental passion flowers

Ornamental passion flower breeders have used many strategies to obtain polyploids (Fischer, 2004FISCHER, E. Hybrids and hybridization. In: ULMER, T. and MACDOUGAL, J. (eds.) Passiflora. Passionflowers of the world. Timber, Portland, 2004. p.362-376.). In general, polyploid individuals have greater vegetative and reproductive vigor as compared with their respective diploids, exhibiting significantly larger floral organs (Stebbins, 1950STEBBINS, G.L. Variation and evolution in plants. Columbia University Press, New York, 1950.; Bharadwaj, 2015BHARADWAJ, D.N. Polyploidy in crop improvement and evolution. In: BAHADUR, B. (Ed.), Plant Biology and Biotechnology: Volume I: Plant Diversity, Organization, Function and Improvement, 2015. pp. 619-637.), despite their reduced fertility. Some allotetraploids have been reported for Passiflora spp. species from conventional hybridization: P. ‘Byron Beauty’ (P. edulis f. flavicarpa × P. edulis f. edulis) × P. incarnata), P. ‘Byte’ (P. edulis × P. incarnata) × (P. incarnata × P. cincinnata), P. ‘Clear Sky’ (P. amethystina × P. caerulea) × P. caerulea) × P. caerulea), P. ‘Fertility’ (P. incarnata × P. cincinnata), P. ‘Inspiration’ (P. incarnata × P. cincinnata), P. ‘Ivy Waves’ (P. coriacea × P. suberosa), P. ‘Jara’ (P. caerulea × P. ‘Purple Haze’), P. ‘Manapany’ [(P. edulis × P. incarnata) × (P. incarnata × P. cincinnata)], P. ‘New Amethyst’ (P. kermesina × P. caerulea), and P. ‘Temptation’ (P. incarnata × P. cincinnata) (Fischer, 2004FISCHER, E. Hybrids and hybridization. In: ULMER, T. and MACDOUGAL, J. (eds.) Passiflora. Passionflowers of the world. Timber, Portland, 2004. p.362-376.).

Because of the triploid nature of the endosperm, the culture of endosperm tissues has been considered a direct method for polyploid production. In Passiflora, in vitro endosperm culture was first performed by Mohamed et al. (1996)MOHAMED, M.E.; HICKS, R.G.T.; BLAKESLEY, D. Shoot regeneration from mature endosperm of Passiflora foetida. Plant Cell Tissue and Organ Culture, v.46, p.161-164, 1996. https://doi:10.1007/BF00034851
https://doi:10.1007/BF00034851...
to obtain triploid P. foetida plants. The authors observed the development of shoots via direct organogenesis, with an average of 1.9 shoots per explant in medium supplemented with 2 μM BA and 5 μM NAA. The triploidy of P. foetida plants regenerated from endosperms was confirmed (data not published). Triploid P. foetida plants also showed greater vegetative vigor and larger leaves and flowers in relation to diploid plants (Figure 3).

Figure 3
Passiflora foetida. (A, B) Leaves of diploid (2n) and triploid (3n) plants. (C-D) Flowers of diploid (2n) and triploid (3n) plants.

The capacity of endosperm tissue to produce triploid and genetically stable plants has also been demonstrated for P. edulis (Antoniazzi et al., 2018ANTONIAZZI, C.A.; FARIA, R.B.; CARVALHO, P.P.; MIKOVSKI, A.I., CARVALHO. I.F.; MATOS, E.M.; REIS, A.C.; VICCINI, L.F.; PAIM PINTO, D.L.; ROCHA, D.I.; OTONI, W.C.; SILVA, M.L. In vitro regeneration of triploid plants from mature endosperm culture of commercial passionfruit (Passiflora edulis Sims). Scientia Horticulturae, v.238, 408-415, 2018. https://doi:10.1016/j.scienta.2018.05.001.
https://doi:10.1016/j.scienta.2018.05.00...
). The highest number of shoots was obtained when the endosperms were cultured in MS medium supplemented with 9.0 μM TDZ. Faria et al. (2018)FARIA, R.B.; CARVALHO, I.F.; ROSSI, A.B.; MATOS, E.M.; ROCHA, D.I.; PAIM PINTO, D.L.; OTONI, W.C.; SILVA, M.L. High responsiveness in de novo shoot organogenesis induction of Passiflora cristalina (Passifloraceae), a wild Amazonian passion fruit species. In Vitro Cell & Development Biology - Plant, v.54, n.2, p.166-174, 2018. https://doi:10.1007/s11627017-9881y.
https://doi:10.1007/s11627017-9881y...
also reported plant regeneration from endosperm culture of P. cristalina in medium supplemented with 8.87 μM BA. However, the ploidy level of regenerated plants was not evaluated.

Somatic hybridization and genetic transformation

Somatic hybridization by protoplasm fusion could be used to generate new ornamental passion flowers with different shapes, colours and sizes. Protoplast-to-plant regeneration systems have been established for a range passion fruit species and novel interespecific somatic hybrids have been obtained between commercial yellow passion fruit and several wild species (Dornelas et al., 1997DORNELAS, M.C.; TAVARES, F.C.A.; OLIVEIRA, J.C.; VIEIRA, M.L.C. Plant regeneration from protoplast fusion in Passiflora spp. Plant Cell Report, v.15, p.106-110, 1997 https://doi:10.1007/BF01690264.
https://doi:10.1007/BF01690264...
; Anthony et al., 1999ANTHONY, P.; OTONI, W.C.; POWER, J.B.; LOWE, K.C.; DAVEY, M.R. Protoplast isolation, culture, and plant regeneration from Passiflora. p.169-181. In: Hall RD. (ed.) Plant Cell Culture Protocols. Humana Press, New York, 1999. https://doi:10.1385/1-59259-583-9:169.
https://doi:10.1385/1-59259-583-9:169...
). However, no hybrids have been produced, by this technique, for ornamental purposes. Considering the diversity of the Passiflora species and the relative simplicity of the protocol, the technology has not been used in its full potential (Rocha et al., 2018ROCHA, D.I.; VIEIRA, L.M.; KOEHLER, A.D.; OTONI, W.C. Cellular and morpho-histological foundations of in vitro plant regeneration. In: LOYOLA-VARGAS, V.M.; OCHOA-ALEJO, N. (Eds.) Plant Cell Culture Protocols, Methods in Moleular Biology, v.1815, Springer, New York, 2018. https://doi:10.1007/978-1-4939-8594-4_3 p.47-68.
https://doi:10.1007/978-1-4939-8594-4_3...
).

Studies on the genetic transformation of passion fruit are also incipient. The systems alredy stablished have been used for generating disease resistant plants (Vieira et al., 2005VIEIRA, M.L.C.; OLIVEIRA, E.J.; MATTA, F.P.; PADÚA, J.G.; MONTEIRO, M. Biotecnological of applied to passionfruit breeding. In: FALEIRO, F.G.; JUNQUEIRA, N.T.V.; BRAGA, M.F. (eds) Passiofruit: germoplasma and breeding. Embrapa Cerrados. Planaltina, 2005. p. 435-453.; Zerbini et al., 2008ZERBINI, F.M.; OTONI, W.C.; VIEIRA, M.L.C. Passionfruit. In: KOLE, C.; T.C. HALL (eds). A compendium of transgenic crop plants-tropical and subtropical fruit and nuts. Wiley, Berlin, 2008. p. 213-134, V.5.). Correa et al. (2015)CORREA, M.F.; PINTO, A.P.C.; REZENDE, J.A.M.; HARAKAVA, R.; MENDES, B.M.J. Genetic transformation of sweet passion fruit (Passiflora alata) and reactions of the transgenic plants to Cowpea aphid borne mosaic virus. European Journal of Plant Pathology, v.143, n.4, p.813-821, 2015. https://doi:10.1007/s10658-015-0733-5
https://doi:10.1007/s10658-015-0733-5...
reported the production of transgenic P. alata lines that contain a Cowpea aphid-borne mosaic virus (CAM V)-derived coat protein gene fragment via A. tumefaciens-mediated transformation. Despite the published reports on genetic transformation of Passiflora genus, it is still a way far from being routine, especially for wild species (Rocha et al., 2018ROCHA, D.I.; VIEIRA, L.M.; KOEHLER, A.D.; OTONI, W.C. Cellular and morpho-histological foundations of in vitro plant regeneration. In: LOYOLA-VARGAS, V.M.; OCHOA-ALEJO, N. (Eds.) Plant Cell Culture Protocols, Methods in Moleular Biology, v.1815, Springer, New York, 2018. https://doi:10.1007/978-1-4939-8594-4_3 p.47-68.
https://doi:10.1007/978-1-4939-8594-4_3...
).

Conservation and cryopreservation of wild Passiflora spp.

The collecting and conserving the diversity of Passiflora germplasm is of great importance, no only as a source of genes and natural products, but also for its ecological value (Pacheco et al., 2016PACHECO, G.; SIMÃO, M.S.; VIANNA, M.G.; GARCIA, R.O.; VIEIRA, M.L.C.; MANSUR, E. In vitro conservation of Passiflora - a review. Scientia Horticulturae, v.211, p.305-311, 2016. https://doi:10.1016/j.scienta.2016.09.004
https://doi:10.1016/j.scienta.2016.09.00...
). Traditionally, Passiflora genetic resources has been conserved in germplasm banks through ex situ conservation strategies (Bernacci et al., 2005BERNACCI, L.C.; MELETTI, L.M.M.; SCOTT, M.D.S.; PASSOS, I.R.S. Espécies de maracujá: Caracterização e conservação da biodiversidade. In: Faleiro FG, Junqueira NTV, Braga MF. (Eds.). Maracujá: germoplasma e melhoramento genético. Planaltina Distrito Federal: Embrapa Cerrados, 2005. p. 559-586.; Cerqueira-Silva et al., 2016CERQUEIRA-SILVA, C.B.M.; FALEIRO, F.G.; JESUS, O.N.; SANTOS, E.S.L.; SOUZA, A.P. The genetic diversity, conservation, and use of passion fruit (Passiflora spp.). In: AHUJA M.R.; JAIN, S.M. (eds.) Genetic diversity and erosion in plants - case histories, v.2. Springer International Publishing, Switzerland, 2016. https://doi:10.1007/978-3-319-25954-3_5. p.215-231.
https://doi:10.1007/978-3-319-25954-3_5...
). It is generally performed inseed banks, although the periodic renewal is limited by the reduction in germination potential, resulting in loss of material. However, some research teams have been focusing in in vitro conservation strategies for the genus (Ávila et al., 2013ÁVILA, T.; MERCADO, G.; AGUILAR, N. Crioconservación de germoplasma vegetal en Bolivia. In: González-Arnao MT, Engelmann F. (eds.). Crioconservación de Plantas en América Latina y el Caribe, IICA, San José, 2013. p. 67-74. https://doi:10.1007/s11627-010-.9327-2.
https://doi:10.1007/s11627-010-.9327-2...
), seed storage (González-Benito et al., 2009GONZÁLEZ-BENITO, M.E.; AGUILAR, N.; ÁVILA, T. Germination and embryo rescue from Passiflora spp. seeds post-cryopreservation. Cryo Letters, v.30, n.2, p.142-147, 2009.; Ávila et al., 2013ÁVILA, T.; MERCADO, G.; AGUILAR, N. Crioconservación de germoplasma vegetal en Bolivia. In: González-Arnao MT, Engelmann F. (eds.). Crioconservación de Plantas en América Latina y el Caribe, IICA, San José, 2013. p. 67-74. https://doi:10.1007/s11627-010-.9327-2.
https://doi:10.1007/s11627-010-.9327-2...
) and cryopreservation (Ávila et al., 2013ÁVILA, T.; MERCADO, G.; AGUILAR, N. Crioconservación de germoplasma vegetal en Bolivia. In: González-Arnao MT, Engelmann F. (eds.). Crioconservación de Plantas en América Latina y el Caribe, IICA, San José, 2013. p. 67-74. https://doi:10.1007/s11627-010-.9327-2.
https://doi:10.1007/s11627-010-.9327-2...
; Pacheco et al., 2016PACHECO, G.; SIMÃO, M.S.; VIANNA, M.G.; GARCIA, R.O.; VIEIRA, M.L.C.; MANSUR, E. In vitro conservation of Passiflora - a review. Scientia Horticulturae, v.211, p.305-311, 2016. https://doi:10.1016/j.scienta.2016.09.004
https://doi:10.1016/j.scienta.2016.09.00...
; Simão et al., 2018SIMÃO, M.J.; COLLIN, M.; GARCIA, R.O.; MANSUR, E.; PACHECO, G.; ENGELMANN F. Histological characterization of Passiflora pohlii Mast. root tips cryopreserved using the V-Cryo-plate technique. Protoplasma, v.255, n.3, p.741-750, 2018. https://doi:10.1007/s00709-017-1182-0
https://doi:10.1007/s00709-017-1182-0...
).

The cryopreservation of passion fruit species has been used to store seeds and in vitro propagules. Due to the difficulties of obtaining seeds from wild populations due to habitat destruction, studies were directed to cryopreservation of shoots and nodal segments. Techniques based on vitrification and encapsulation-vitrification are most often used (Ávila et al., 2013ÁVILA, T.; MERCADO, G.; AGUILAR, N. Crioconservación de germoplasma vegetal en Bolivia. In: González-Arnao MT, Engelmann F. (eds.). Crioconservación de Plantas en América Latina y el Caribe, IICA, San José, 2013. p. 67-74. https://doi:10.1007/s11627-010-.9327-2.
https://doi:10.1007/s11627-010-.9327-2...
; Pacheco et al., 2016PACHECO, G.; SIMÃO, M.S.; VIANNA, M.G.; GARCIA, R.O.; VIEIRA, M.L.C.; MANSUR, E. In vitro conservation of Passiflora - a review. Scientia Horticulturae, v.211, p.305-311, 2016. https://doi:10.1016/j.scienta.2016.09.004
https://doi:10.1016/j.scienta.2016.09.00...
). The plant vitrification protocol has been used for P. tarminiana, P. pinnatistipula and P. mollissima (Ávila et al., 2013ÁVILA, T.; MERCADO, G.; AGUILAR, N. Crioconservación de germoplasma vegetal en Bolivia. In: González-Arnao MT, Engelmann F. (eds.). Crioconservación de Plantas en América Latina y el Caribe, IICA, San José, 2013. p. 67-74. https://doi:10.1007/s11627-010-.9327-2.
https://doi:10.1007/s11627-010-.9327-2...
). Vianna et al. (2012)VIANNA, M.G.; FERREIRA, A.L.; GARCIA, R.O.; FALCÃO, E.; PACHECO, G.; MANSUR, E. Comparison of vitrification-based techniques in the efficacy of cryopreservation of Passiflora suberosa L. and P. foetida L. shoot tips. Cryobiologia, v.65, p.346, 2012. https://doi:10.1016/j.cryobiol.2012.07.024
https://doi:10.1016/j.cryobiol.2012.07.0...
observed post-freeze recovery of 60% only with P. foetida shoots when cryopreserved using the encapsulation-vitrification protocol. Nodal segments often not chosen for cryopreservation. Nevertheless, a successful cryopreservation protocol for nodal segments of in vitro plants of P. pohlii was developed by Merhy et al. (2014)MERHY, T.S.M.; VIANNA, M.G.; GARCIA, R.O.; PACHECO, G.; MANSUR, E. Cryopreservation of Passiflora pohlii nodal segments and assessment of genetic stability of regenerated plants. Cryo Letters, v.35, n.3, p.204-15, 2014. https://doi:10.1038/sj.bjp.0705776.
https://doi:10.1038/sj.bjp.0705776...
using the vitrification technique. Despite recent advances, future prospects include optimization of existing cryopreservation protocols, as well as innovative approaches to in vitro conservation of Passiflora species (Pacheco et al., 2016PACHECO, G.; SIMÃO, M.S.; VIANNA, M.G.; GARCIA, R.O.; VIEIRA, M.L.C.; MANSUR, E. In vitro conservation of Passiflora - a review. Scientia Horticulturae, v.211, p.305-311, 2016. https://doi:10.1016/j.scienta.2016.09.004
https://doi:10.1016/j.scienta.2016.09.00...
).

Acknowledgments

This work was supported by Fundação de Amparo à Pesquisa do Estado de Mato Grosso (FAPEMAT) (Cuiabá, MT) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (Brasília, DF, Brazil).

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Publication Dates

  • Publication in this collection
    12 Aug 2019
  • Date of issue
    Apr-Jun 2019

History

  • Received
    17 May 2019
  • Accepted
    03 July 2019
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