苦苣苔科植物因其多樣、顯眼和吸引人的花葉圖案而被以各種創新方式用於室內外景觀。 非洲菫屬(Saintpaulia)和岩桐屬(Sinningia)是苦苣苔科中廣泛在市場上流通和最具知名的兩屬植物，其他屬則較不被認識和流通性少，開發具有更強抗蟲和抗病性、耐高/低溫性、更佳的開花特性和更高觀賞價值的新雜交品種是極具吸引力的。新雜交品種可以通過雜交授粉產生，但前提是花粉和柱頭在授粉時是具有活性和感受性的，有關苦苣苔科雜交授粉的科學研究非常有限，因此，本研究旨在定義授粉時間，進行種間和屬間雜交，並評估雜交植物的形態。 本研究使用九屬共19 種苦苣苔科植物，包括 Achimenes flava、 Alsobia ‘Cygnet’、Deinostigma eberhardtii、Deinostigma tamiana、Episcia ‘Blue Nile’、Episcia ‘Jim’s Canadian Sunset’、Episcia ‘Lil Lemon’、Episcia ‘Silver Skies’、Episcia ‘Thad’s Yellow Bird’, Episcia ‘Tiger Stripe’, Kohleria ‘Brimstone’, Kohleria ‘HCY’s Sevinalla’, Saintpaulia ‘Lyon’s Party Parasol’, Sinningia ‘HCY’s Peach Fragrance’, Sinningia ‘Mark Twain’, Smithiantha ‘An’s Hanabi’, Smithiantha ‘Petite Chérie’，Smithiantha salmon hybrid 和，Stretocarpella saxorum。首先，通過在含有不同濃度蔗糖（10、20 或 30%）、硼酸（50、100、200 或 400 毫克/升）和硝酸鈣（200 或 400 毫克/升）的培養基上進行體外花粉萌發試驗，研究結果顯示，含有 10% 蔗糖的培養基優於含 20% 和 30% 蔗糖的培養基，硼酸在 50 毫克/升的劑量下顯著增加花粉萌發和花粉管生長，硝酸鈣在 200 或 400 毫克/升時對花粉萌發和花粉管生長有效，因此選擇含有10%蔗糖、50 毫克/升硼酸和200毫克/升硝酸鈣的培養基來進行後續實驗。從開花到花衰每日評估花粉活力，發現花粉採集的最佳時機為開花後第1天。基於雌蕊長度和柱頭形態分析柱頭的感受性，發現依據測試植物的不同，在開花後 3 至 20 天有較高的柱頭感受性，最常柱頭長度為2.03-3.50公分，成熟的柱頭比不成熟的柱頭有更好的柱頭感受性。通過人工授粉進行種間和屬間雜交，從 105個雜交組合中獲得了 11 個成功的種間雜交（50%）和 13個屬間雜交（15.6%），種間雜交 (36.3%) 比屬間雜交 (3.6%) 產生更多有活性的種子，目前針對十四種具有潛力的種間和屬間雜種進行外貌形態和市場潛力評估。

Gesneriaceae plants have been used in a variety of innovative ways in landscaping and indoors because of their diverse, conspicuous, attractive flower and leaf patterns. Plants of the genera Saintpaulia and Sinningia are widely commercialized in the market and are the most known of the family Gesneriaceae. Plants of the other genera are less popular and not readily available commercially. There is a high interest to develop new hybrids with improved resistance to pests, diseases and high/low temperatures, better blooming properties, or enhanced ornamental values. New hybrids can be created via cross pollination, which requires that the pollens are viable and stigmas are receptive at the time of the crosses. However, scientific studies on cross pollination are very limited in this family. Hence, this study was aimed to define the timing for pollination, conduct interspecific and intergeneric crosses, and evaluating the morphology of the hybrid plants. This study made use of nineteen gesneriad plants from nine genera, including Achimenes flava, Alsobia ‘Cygnet’, Deinostigma eberhardtii, Deinostigma tamiana, Episcia ‘Blue Nile’, Episcia ‘Jim’s Canadian Sunset’, Episcia ‘Lil Lemon’, Episcia ‘Silver Skies’, Episcia ‘Thad’s Yellow Bird’, Episcia ‘Tiger Stripe’, Kohleria ‘Brimstone’, Kohleria ‘HCY’s Sevinalla’, Saintpaulia ‘Lyon’s Party Parasol’, Sinningia ‘HCY’s Peach Fragrance’, Sinningia ‘Mark Twain’, Smithiantha ‘An’s Hanabi’, Smithiantha ‘Petite Chérie’, Smithiantha salmon hybrid, Stretocarpella saxorum. First, in vitro pollen germination on medium enriched with varied amounts of sucrose (10%, 20%, or 30%), boric acid (50, 100, 200, or 400 mg/l), and calcium nitrate (200 or 400 mg/l) was used to assess pollen viability. The results showed that media containing 10% sucrose outperformed media with 20 and 30% sucrose. Boric acid, at a dosage of 50 mg/l, significantly enhanced pollen germination and pollen tube length. At 200 or 400 mg/l, calcium nitrate proved helpful in promoting pollen germination and pollen tube growth. Later studies were carried out using a medium with 10% sucrose, 50 mg/l boric acid, and 200 mg/l calcium nitrate. The viability of pollens from anthesis to flower senescence was evaluated daily and it was found that the optimum time for collecting pollens was at day 1 after anthesis. The receptivity of stigma was analyzed based on pistil length and stigma morphology. The longest pistil length was observed from 3 to 20 days after anthesis depending on the plant tested varied from 2.03 to 3.50 cm. Mature stigmas appeared to be more receptive than immature ones. Interspecific and intergeneric crosses were performed by hand pollination. A total of 105 cross combinations were made from which eleven successful interspecific crosses (50%) and thirteen intergeneric crosses (15.6%) were obtained. Interspecific crosses (36.3%) produced more viable seeds than intergeneric crosses (3.6%). Fourteen interspecific and intergeneric hybrids of interest are undergoing morphological and market potential evaluations.

Abdelgadir, H., S. Johnson, and J. Van Staden. 2012. Pollen Viability, Pollen Germination and Pollen Tube Growth in the Biofuel Seed Crop Jatropha curcas (Euphorbiaceae). South African Journal of Botany 79: 132-139.
Acar, I., B. E. Ak, and K. Sarpkaya. 2010. Effects of Boron and Gibberellic Acid on In Vitro Pollen Germination of Pistachio (Pistacia vera L.). African Journal of Biotechnology 9(32): 5126-5130.
Acar, I. and V. G. Kakani. 2010. The Effects of Temperature on In Vitro Pollen Germination and Pollen Tube Growth of Pistacia Spp. Scientia Horticulturae 125(4): 569-572.
Afkhami-Sarvestani, R., M. Serek, and T. Winkelmann. 2012. Protoplast Isolation and Culture from Streptocarpus, Followed by Fusion with Saintpaulia Ionantha Protoplasts. European Journal of Horticultural Science 77(6): 249.
Aguilera, F. and L. Ruiz Valenzuela. 2013. Time Trend in the Viability of Pollen Grains in the ‘Picual’ olive (Olea europaea L.) Cultivar. Palynology 37(1): 28-34.
Al-Yasiri, S. and D. Coyne. 1964. Effect of Growth Regulators in Delaying Pod Abscission and Embryo Abortion in the Interspecific Cross Phaseolus vulgaris× P. acutifolius. Crop Science 4(4): 433-435.
Anonymous. 2002. Saintpaulia Self-Pollination. African Violet Magazine 55(6): 3.
Anton, W., C. J. L, and M. Michael. 2013. A New Formal Classification of Gesneriaceae. Selbyana: 68-94.
Arisumi, T. 1964. Interspecific Hybridization in African Violets. Journal of Heredity 55(4): 181-183.
Ashman, T.-L. and D. J. Schoen. 1996. Floral Longevity: Fitness Consequences and Resource Costs, in Floral Biology: Springer, 112-139.
Baack, E. J. and L. H. Rieseberg. 2007. A Genomic View of Introgression and Hybrid Speciation. Current Opinion in Genetics & Development 17(6): 513-518.
Báez, P., M. Riveros, and C. Lehnebach. 2002. Viability and Longevity of Pollen of Nothofagus Species in South Chile. New Zealand Journal of Botany 40(4): 671-678.
Bates, L. and C. Deyoe. 1973. Wide Hybridization and Cereal Improvement. Economic Botany 27(4): 401-412.
Beardsell, D., S. Obrien, E. Williams, R. Knox, and D. Calder. 1993. Reproductive Biology of Australian Myrtaceae. Australian Journal of Botany 41(5): 511-526.
Bleckmann, A., S. Alter, and T. Dresselhaus. 2014. The Beginning of a Seed: Regulatory Mechanisms of Double Fertilization. Frontiers in Plant Science 5: 452.
Boggan, J. 1996. Fragrant Flowers in Gesneriaceae. Gloxinian 46: 17-27.
Boland, D. and M. Sedgley. 1986. Stigma and Style Morphology in Relation to Taxonomy and Breeding Systems in Eucalyptus and Angophora (Myrtaceae). Australian Journal of Botany 34(5): 569-584.
Bremer, K., E. Friis, and B. Bremer. 2004. Molecular Phylogenetic Dating of Asterid Flowering Plants Shows Early Cretaceous Diversification. Systematic Biology 53(3): 496-505.
Brys, R. and H. Jacquemyn. 2015. Disruption of the Distylous Syndrome in Primula veris. Annals of Botany 115(1): 27-39.
Burtt, B. 1954. Studies in the Gesneriaceae of the Old World. I. General Introduction. Notes from Royal Botanic Garden Edinburgh 21: 185-218.
Charlesworth, D. and B. Charlesworth. 1987. Inbreeding Depression and Its Evolutionary Consequences. Annual Review of Ecology and Systematics 18(1): 237-268.
Chen, H., M. Mok, and D. Mok. 1990. Somatic Embryogenesis and Shoot Organogenesis from Interspecific Hybrid Embryos of Vigna glabrescens and V. radiata. Plant Cell Reports 9(2): 77-79.
Clarke, A., J. Considine, R. Ward, and R. Knox. 1977. Mechanism of Pollination in Gladiolus: Roles of the Stigma and Pollen-Tube Guide. Annals of Botany 41(1): 15-20.
CYSIP (Central Yukon Species Inventory Project). 2021. Leaf Glossary. Retrieved on August 2, 2021, from World Wide Web: http://www.flora.dempstercountry.org/Leaf.Glossary.html.
Dabgar, Y. and B. Jain. 2001. Effect of Sucrose, Boron, Calcium and Magnesium During In Vitro Pollen Germination and Tube Growth in Abelmoscus esculentus L. Moench. Journal of Swamy Botanical 18: 25-29.
Dane, F. and N. Ekici. 2011. Pollen Tube Growth of Paeonia tenuifolia L. (Paeoniaceae) In Vitro and In Vivo. Bangladesh Journal of Botany 40(1): 93-95.
Datta, S. and J. Teixeira da Silva. 2006. Role of Induced Mutagenesis for Development of New Flower Colour and Type in Ornamentals. Floriculture, Ornamentals and Plant Biotechnology: Advances and Tropical issues. Mutations and Mutagénesis: 640-645.
De Nettancourt, D. 2013. Incompatibility in Angiosperms. Vol. 3: Springer Science & Business Media.
Dickinson, D. B. 1967. Permeability and Respiratory Properties of Germinating Pollen. Physiologia Plantarum 20(1): 118-127.
Dickinson, G. R., D. J. Lee, and H. M. Wallace. 2012. The Influence of Pre-and Post-Zygotic Barriers on Interspecific Corymbia Hybridization. Annals of Botany 109(7): 1215-1226.
Dumas, C., R. Knox, and T. Gaude. 1984. Pollen-Pistil Recognition: New Concepts from Electron Microscopy and Cytochemistry. International Review of Cytology 90: 239-272.
Edlund, A. F., R. Swanson, and D. Preuss. 2004. Pollen and Stigma Structure and Function: The Role of Diversity in Pollination. The Plant Cell 16 (suppl_1): S84-S97.
Ellis, M. and M. Sedgley. 1992. Floral Morphology and Breeding System of Three Species of Eucalyptus, Section Bisectaria (Myrtaceae). Australian Journal of Botany 40(3): 249-262.
Fang, J.-Y. and S. Traore. 2011. In Vitro Mutation Induction of Saintpaulia Using Ethyl Methanesulfonate. HortScience 46(7): 981-984.
Ferri, A., E. Bellini, G. Padula, and E. Giordani. 2008. Viability and In Vitro Germinability of Pollen Grains of Olive Cultivars and Advanced Selections Obtained in Italy. Viability and In Vitro Germinability of Pollen Grains of Olive Cultivars and Advanced Selections Obtained in Italy: 1000-1007.
Fragallah, S. A. D. A., P. Wang, N. Li, Y. Chen, and S. Lin. 2018. Metabolomic Analysis of Pollen Grains with Different Germination Abilities from Two Clones of Chinese Fir (Cunninghamia lanceolata (Lamb) Hook). Molecules 23(12): 3162.
Frankel, R. and E. Galun. 2012. Pollination Mechanisms, Reproduction and Plant Breeding. Vol. 2: Springer Science & Business Media.
Freeman, C. E., R. D. Worthington, and M. S. Jackson. 1991. Floral Nectar Sugar Compositions of Some South and Southeast Asian Species. Biotropica: 568-574.
Galen, C., K. A. Zimmer, and M. E. Newport. 1987. Pollination in Floral Scent Morphs of Polemonium viscosum: A Mechanism for Disruptive Selection on Flower Size. Evolution 41(3): 599-606.
Geier, T. 1989. An Improved Type of' Kohleria Obtained through In Vitro Chemical Mutagenesis. Breeding Newsletter 34:7-8.
Heslop-Harrison, Y. 2000. Control Gates and Micro-Ecology: The Pollen-Stigma Interaction in Perspective. Annals of Botany 85 (suppl_1): 5-13.
Heywood, V. H., R. Brummitt, A. Culham, and O. Seberg. 2007. Flowering Plant Families of the World. Vol. 88: Firefly Books Ontario.
Hoefert, L. 1971. Pollen Grain and Sperm Cell Ultrastructure in Beta, in Pollen: Elsevier, 68-69.
Hussain, S. and W. Williams. 2008. The Use of Endosperm Balance Number for Predicting Gamete Selection in Complex Polyploid Interspecific Trifolium repens × T. nigrescens Crosses. Plant Breeding 127(5): 518-523.
Imaichi, R., S. Inokuchi, and M. Kato. 2001. Developmental Morphology of One-Leaf Plant Monophyllaea singularis (Gesneriaceae). Plant Systematics and Evolution 229(3): 171-185.
Jackson, S. and R. Hanneman. 1999. Crossability between Cultivated and Wild Tuber-and Non-Tuber-Bearing Solanums. Euphytica 109(1): 51-67.
James, E. and R. Knox. 1993. Reproductive-Biology of the Australian Species of the Genus Pandorea (Bignoniaceae). Australian Journal of Botany 41(5): 611-626.
Jayaprakash, P. 2018. Pollen Germination In Vitro. Pollination in Plants: 81.
Johnston, S., T. Den Nijs, S. Peloquin, and R. Hanneman. 1980. The Significance of Genic Balance to Endosperm Development in Interspecific Crosses. Theoretical and Applied Genetics 57(1): 5-9.
Johnston, S. and R. Hanneman. 1982. Manipulations of Endosperm Balance Number Overcome Crossing Barriers between Diploid Solanum Species. Science 217(4558): 446-448.
Jong, K. 1970. Developmental Aspects of Vegetative Morphology in Streptocarpus. University of Edinburgh.
Kadereit, J. W. 2004. Flowering Plants Dicotyledons: Lamiales (except Acanthaceae Including Avicenniaceae). Vol. 7: Springer Science & Business Media.
Kakani, V., K. Reddy, S. Koti, T. Wallace, P. Prasad, V. Reddy, and D. Zhao. 2005. Differences in In Vitro Pollen Germination and Pollen Tube Growth of Cotton Cultivars in Response to High Temperature. Annals of Botany 96(1): 59-67.
Kelly, J. D. and V. Vallejo. 2006. QT1 Analysis of Multigenic Disease Resistance in Plant Breeding, in Multigenic and Induced Systemic Resistance in Plants: Springer, 21-48.
Kharkwal, M. C. and H. K. Jain. 2004. Mendelian to Molecular Approaches. Edited by H. K. Jain, and M. C. Kharkwal, Plant Breeding: Mendelian to Molecular Approaches. In: Classical and Molecular Concepts of Heterosis.
Kolehmainen, J., H. Korpelainen, and P. Mutikainen. 2010. Inbreeding and Inbreeding Depression in a Threatened Endemic Plant, the African Violet (Saintpaulia Ionantha ssp. Grotei), of the East Usambara Mountains, Tanzania. African Journal of Ecology 48(3): 576-587.
Kolehmainen, J. K. and P. Mutikainen. 2006. Reproductive Ecology of Three Endangered African Violet (Saintpaulia H. Wendl.) Species in the East Usambara Mountains, Tanzania. African Journal of Ecology 44(2): 219-227.
Kremer, D. and T. Jemrie. 2006. Pollen Germination and Pollen Tube Growth in Fraxinus pennsylvanica. Biologia 61(1): 79-83.
Kushikawa, S., Y. Hoshino, and M. Mii. 2001. Agrobacterium-Mediated Transformation of Saintpaulia ionantha Wendl. Plant Science 161(5): 953-960.
Kushikawa, S., K. Miyoshi, and M. Mii. 2002. Pre-Culture Treatment Enhances Transient Gus Gene Expression in Leaf Segment of Saintpaulia ionantha Wendl. After Inoculation with Agrobacterium tumefaciens. Plant Biotechnology 19(2): 149-152.
Kvist, L. P. and L. E. Skog. 1988. Columnea incredibilis and Cremosperma fdicifolium‐Two Remarkable New Gesneriaceae from Western Colombia. Nordic Journal of Botany 8(3): 253-257.
Lee, C. B., L. E. Page, B. A. McClure, and T. P. Holtsford. 2008. Post-Pollination Hybridization Barriers in Nicotiana Section Alatae. Sexual Plant Reproduction 21(3): 183-195.
Lei, W., G. Qiu, W. Yin-Zheng, and L. Qi-Bing. 2005. Isolation and Sequence Analysis of Two CYC-Like Genes, SICYC1A and SICYC1B, from Zygomorphic and Actinomorphic Cultivars of Saintpaulia ionantha (Gesneriaceae). Journal of Systematics and Evolution 44(4): 353-361.
Lima-Brito, J., H. Guedes-Pinto, and J. Heslop-Harrison. 1998. The Activity of Nucleolar Organizing Chromosomes in Multigeneric F1 Hybrids Involving Wheat, Triticale, and Tritordeum. Genome 41(6): 763-768.
Lin, Y., Y. Wang, A. Iqbal, P. Shi, J. Li, Y. Yang, and X. Lei. 2017. Optimization of Culture Medium and Temperature for the In Vitro Germination of Oil Palm Pollen. Scientia Horticulturae 220: 134-138.
Linskens, H. 1967. Isolation of Ribosomes from Pollen. Planta 73(2): 194-200.
Lloyd, D. G. and C. Webb. 1986. The Avoidance of Interference between the Presentation of Pollen and Stigmas in Angiosperms I. Dichogamy. New Zealand Journal of Botany 24(1): 135-162.
Mallet, J. 2005. Hybridization as an Invasion of the Genome. Trends in Ecology & Evolution 20(5): 229-237.
Mattsson, O., R. Knox, J. Heslop-Harrison, and Y. Heslop-Harrison. 1974. Protein Pellicle of Stigmatic Papillae as a Probable Recognition Site in Incompatibility Reactions. Nature 247(5439): 298-300.
Mercuri, A., L. De Benedetti, G. Burchi, and T. Schiva. 2000. Agrobacterium-Mediated Transformation of African Violet. Plant Cell, Tissue and Organ Culture 60(1): 39-46.
Navarro, L. 1997. Is the Dichogamy of Salvia verbenaca (Lamiaceae) an Effective Barrier to Self-Fertilization? Plant Systematics and Evolution 207(1): 111-117.
Newbery, D. 1995. Ma Huston, Biological Diversity: The Coexistence of Species on Changing Landscapes. Journal of Tropical Ecology 11(4): 568-568.
Nishii, K., M. Hughes, M. Briggs, E. Haston, F. Christie, M. J. DeVilliers, T. Hanekom, W. G. Roos, D. U. Bellstedt, and M. Möller. 2015. Streptocarpus Redefined to Include All Afro‐Malagasy Gesneriaceae: Molecular Phylogenies Prove Congruent with Geographical Distribution and Basic Chromosome Numbers and Uncover Remarkable Morphological Homoplasies. Taxon 64(6): 1243-1274.
Nishiyama, I. and N. Inomata. 1966. Embryological Studies on Cross-Incompatibility between 2x and 4x in Brassica. The Japanese Journal of Genetics 41(1): 27-42.
O'Brien, S. P. 1994. Pistil Structure and Pollen Tube Pathways in Leptospermum myrsinoides and L. continentale (Myrtaceae). Annals of Botany 73(3): 225-230.
O'Brien, S. P., B. R. Loveys, and W. Grant. 1996. Ultrastructure and Function of Floral Nectaries of Chamelaucium Uncinatum (Myrtaceae). Annals of Botany 78(2): 189-196.
Ottaviano, E. and D. L. Mulcahy. 1989. Genetics of Angiosperm Pollen. Advances in Genetics 26: 1-64.
Palanivelu, R. and T. Tsukamoto. 2012. Pathfinding in Angiosperm Reproduction: Pollen Tube Guidance by Pistils Ensures Successful Double Fertilization. Wiley Interdiscip Reviews Development Biology 1(1): 96-113.
Palser, B. F., J. L. Rouse, and E. G. Williams. 1989. Coordinated Timetables for Megagametophyte Development and Pollen Tube Growth in Rhododendron nuttallii from Anthesis to Early Postfertilization. American Journal of Botany 76(8): 1167-1202.
Parton, E., I. Vervaeke, R. Delen, B. Vandenbussche, R. Deroose, and M. De Proft. 2002. Viability and Storage of Bromeliad Pollen. Euphytica 125(2): 155-161.
Perret, M., A. Chautems, A. O. De Araujo, and N. Salamin. 2013. Temporal and Spatial Origin of Gesneriaceae in the New World Inferred from Plastid DNA Sequences. Botanical Journal of the Linnean Society 171(1): 61-79.
Perret, M., A. Chautems, R. Spichiger, M. Peixoto, and V. Savolainen. 2001. Nectar Sugar Composition in Relation to Pollination Syndromes in Sinningieae (Gesneriaceae). Annals of Botany 87(2): 267-273.
Reed, S. M. 2001. Hydrangeas for the Future. Paper read at Combined Proceedings-International Plant Propagators Society 51: 457-460.
Rodríguez-Riaño, T. and A. Dafni. 2007. Pollen-Stigma Interference in Two Gynodioecious Species of Lamiaceae with Intermediate Individuals. Annals of Botany 100(2): 423-431.
Russell, P. J. 2010. Mendelian Genetics.p. 297-325. In iGenetics A Molecular Approach 3rd ed. Pearson Benjamin Cummings. California. USA. Molecular Approach. California. USA.: Pearson Benjamin Cummings.
Sabja, A. M., D. W. Mok, and M. C. Mok. 1990. Seed and Embryo Growth in Pod Cultures of Phaseolus vulgaris and P. vulgaris × P. acutifolius. HortScience 25(10): 1288-1291.
Sahar, N. and P. Spiegel-Roy. 1984. In Vitro Germination of Avocado Pollen. HortScience 19(6): 886-888.
SanMartin-Gajardo, I. and J. R. S. Vianna. 2010. Pollination of Nematanthus brasiliensis: An Epiphytic Gesneriaceae Endemic to the Southeastern Atlantic Forests of Brazil. Selbyana: 216-220.
Saueregger, J. and A. Weber. 2003. Factors Controlling Initiation and Orientation of the Macrocotyledon in Anisocotylous Gesneriaceae. Edinburgh Journal of Botany 60(3): 467-482.
Schueler, S., K. H. Schlünzen, and F. Scholz. 2005. Viability and Sunlight Sensitivity of Oak Pollen and Its Implications for Pollen-Mediated Gene Flow. Trees 19(2): 154-161.
Sedgley, M. 1989. Ovule and Seed Development in Eucalyptus woodwardii Maiden (Symphyomyrtus). Botanical Gazette 150(3): 271-280.
Sedgley, M., F. Hand, R. Smith, and A. Griffin. 1989. Pollen Tube Growth and Early Seed Development in Eucalyptus regnans F. Muell. (Myrtaceae) in Relation to Ovule Structure and Preferential Outcrossing. Australian Journal of Botany 37(5): 397-411.
Sherriff, L. 1994. Nerine Breeding Systems. Honour Thesis, University of Tasmania.
Shivanna, K., H. Linskens, and M. Cresti. 1991. Pollen Viability and Pollen Vigor. Theoretical and Applied Genetics 81(1): 38-42.
Shivanna, K. and N. Rangaswamy. 1992. Pollen-Pistil Interaction, in Pollen Biology: Springer, 45-60.
Sidhu, R. J. and C. Malik. 1986. Metabolic Role of Boron in Germinating Pollen and Growing Pollen Tubes, in Biotechnology and Ecology of Pollen: Springer, 373-378.
Skog, L. E. 1976. A Study of the Tribe Gesneriaceae, with a Revision of Gesneria (Gesneriaceae-Gesnerioideae). Smithsonian Contributions to Botany 29:1-182
Stanley, R. G. and F. A. Loewus. 1964. Boron and Myo-Inositol in Pollen Pectin Biosynthesis. Pollen Physiology and Fertilization: 128-136.
Steinhorst, L. and J. Kudla. 2013. Calcium-a Central Regulator of Pollen Germination and Tube Growth. Biochimica et Biophysica Acta (BBA)-Molecular Cell Research 1833(7): 1573-1581.
Stephenson, A. G. 1981. Flower and Fruit Abortion: Proximate Causes and Ultimate Functions. Annual Review of Ecology and Systematics 12: 253-279.
Stewart, D., E. Graciet, and F. Wellmer. 2016. Molecular and Regulatory Mechanisms Controlling Floral Organ Development. The FEBS Journal 283(10): 1823-1830.
Stone, J. L., J. D. Thomson, and S. J. Dent‐Acosta. 1995. Assessment of Pollen Viability in Hand‐Pollination Experiments: A Review. American Journal of Botany 82(9): 1186-1197.
Sulusoglu, M. and A. Cavusoglu. 2014. In Vitro Pollen Viability and Pollen Germination in Cherry Laurel (Prunus laurocerasus L.). The Scientific World Journal 2014.
Tuinstra, M. and J. Wedel. 2000. Estimation of Pollen Viability in Grain Sorghum. Crop Science 40(4): 968-970.
Twell, D. 2011. Male Gametogenesis and Germline Specification in Flowering Plants. Sexual Plant Reproduction 24(2): 149-160.
Van Laere, K., J. M. Van Huylenbroeck, and E. Van Bockstaele. 2007. Interspecific Hybridisation between Hibiscus syriacus, Hibiscus sinosyriacus and Hibiscus paramutabilis. Euphytica 155(1): 271-283.
Vasil, I. 1974. Histology and Physiology of Pollen Germination and Pollen Tube Growth on the Stigma and in the Style. In Proceedings International Symposium on Fertilization in Higher Plants 105-118.
Vaughton, G. and M. Ramsey. 1991. Floral Biology and Inefficient Pollen Removal in Banksia spinulosa Var Neoanglica (Proteaceae). Australian Journal of Botany 39(2): 167-177.
Wang, Q., L. Lu, X. Wu, Y. Li, and J. Lin. 2003. Boron Influences Pollen Germination and Pollen Tube Growth in Picea meyeri. Tree Physiology 23(5): 345-351.
Wang, W., K. Pan, and Z. Li. 1992. Keys to the Gesneriaceae of China. Edinburgh Journal of Botany.
Wang, W., L. Zhou, Y. Huang, Z. Bao, and H. Zhao. 2014. Reproductive Barriers in Interspecific Hybridizations among Chimonanthus praecox (L.) Link, C. salicifolius Sy Hu, and C. nitens Oliver from Pollen-Pistil Interaction and Hybrid Embryo Development. Scientia Horticulturae 177: 85-91.
Weber, A. 1982. Evolution and Radiation of the Pair-Flowered Cyme in Gesneriaceae. Autralian Systematic Botany Society Newsletter 30: 23-41
Weber, A. 1995. Developmental Aspects of the Pair-Flowered Cyme of Gesneriaceae. Gesneriana 1(1): 18-28.
Weber, A., J. L. Clark, and M. Möller. 2013. A New Formal Classification of Gesneriaceae. Selbyana: 68-94.
Wiehler, H. 1983. A Synopsis of the Neotropical Gesneriaceae. Selbyana 6(1/4): 1-219.
Wiehler, H. 1994. A Re‐Examination of Sanango Racemosum. 4. Its New Systematic Position in Gesneriaceae. Taxon 43(4): 625-632.
Wiens, D., C. Calvin, C. Wilson, C. Davern, D. Frank, and S. Seavey. 1987. Reproductive Success, Spontaneous Embryo Abortion, and Genetic Load in Flowering Plants. Oecologia 71(4): 501-509.
Williams, E. 1987. Interspecific Hybridization in Pasture Legumes. Plant Breeding Reviews 5: 237-306.
Woo, S. H., A. Mostafa Kamal, S. Tatsuro, C. G. Campbell, T. Adachi, Y. H. Yun, K. Y. Chung, and J. S. Choi. 2010. Buckwheat (Fagopyrum esculentum Moench.): Concepts, Prospects and Potential. European Journal of Plant Science and Biotechnology 4: 1-16.
Yang, W.-C. and V. Sundaresan. 2000. Genetics of Gametophyte Biogenesis in Arabidopsis. Current Opinion in Plant Biology 3(1): 53-57.
Zhang, X. L., X. X. Li, L. Y. Ni, and Y. H. Guo. 2011. When Interspecific Prezygotic Barriers Break Down: Hybridization between Two Potamogeton Species (P. wrightii and P. perfoliatus) and Comparison of the Artificial and Natural Hybrids. Plant Systematics and Evolution 295(1): 119-128.
Zhao, P., L. Zhao, Q. Sheng, S. Li, and H. Peng. 2011. The Days Anthesis in Relation to the Floral Shapes, Pollen Size, and S-Rnase Gene Identifying in Self incompatibility of Wild Species. African Journal of Biotechnology 10(65): 14319-14328.