TRIPLOID VARIETIES OF PETUNIA HYBRIDA PERSPECTIVE BREEDING POSSIBILITY

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1 TRIPLOID VARIETIES OF PETUNIA HYBRIDA PERSPECTIVE BREEDING POSSIBILITY JOSEF CERNY, MARKETA CERNA, PETR SALAS Department of Breeding and Propagation of Horticultural Plants Mendel University in Brno Valticka 337, Lednice CZECH REPUBLIC Abstract: Petunia hybrida is an important annual plant. Current assortment of Petunias consists mainly of generatively propagated F1 varieties. Vegetatively propagated varieties are nowadays increasingly gaining popularity. In this experiment was successfully verified the possibility to create tetraploid varieties that would be propagated vegetatively. Large flowered hybrids with genotype Ggg were obtained. As a maternal component tetraploid genotype gggg and as a paternal component diploid GG genotype was used. From the seeds received from pollinating 120 flowers were obtained 10 triploid hybrids. Diameter of the flowers was 98 mm, which is 25% more when compared to parental component with big flowers. The growth characteristics as well as the health conditions were good. This is a new perspective possibility to create new varieties of Petunia hybrida. Key Words: Petunia hybrida, triploid, G allele, variety, breeding INTRODUCTION Petunia hybrida belongs to the trio of the world's most important and popular annuals (Anderson 2007). It is subject of intensive breeding, mainly of American and Japanese companies (Murphy 2007). The core assortment consists of F1 varieties in the type multiflora and grandiflora (Ball 1991). A special group in assortment represent tetraploid varieties Petunia h. superbissima. This group was very popular in the early twentieth century with the launch of hybrid varieties to the market in the fifties, this type of Petunias nearly disappeared from the catalogues of seed companies (Gerats and Strommer 2009). Superbissima type varieties are tetraploid (2 n = 28) (Matsuda 1933) and like most tetraploids are characterized by robustness of plants and flowers. Flower diameter is 160 mm (Maatsch and Nolting 1968, Reimann-Philipp 1969). Currently, F1 supperbissima hybrids don t exist. Nor vegetative propagation - cuttings, which is used for multiplication of varieties of Petunias increasingly, is suitable for this type. Multiplying coefficient of tetraploids is very low. Yet completely unused option is the creation of large flowered triploid varieties, that would be then propagated vegetatively. The flower size is in Petunia controlled by a dominant gene G (Plickert 1936) which is located on chromosome V (Cornu et al. 1980). Heterozygote Gg is a grandiflora, which is used in the creation of large flowered commercial F1 varieties. Homozygous paternal component with GG genotype is not very vivid. After crossing tetraploid and diploid plants mostly non germinating seeds are obtained. Only when a maternal component is tetraploid and paternal component is diploid, then in rare cases triploid hybrid could be found (Plickert 1936). Triploid plant with genotype Ggg could combine big flower diameter, good growth characteristics and acceptable propagation coefficient needed for intensive vegetative propagation. Visual characteristics could be very similar to the attractive OP tetraploid varieties, but without their limitations and disadvantages (disparity, flowers deformations, bad plant habitus). MATERIAL AND METHODS Characterization of experimental design and methods Plant growing and crossing were carried out in a greenhouse isolated against insects. Plants were grown in a commercial substrate manufactured by company Gramoflor. Once a week the plants were 711 P age

2 fertilized. Plant protection was performed according to occurrence of diseases and pests. All plants were grown under the same conditions. Genetic materials used in the experiment were provided by company Černý-BioPro Ltd., Prague. In 2013, a small pink flowered plant was selected from the group of plants of OP tetraploid variety Rosea. It was assumed to be homozygous recessive genotype gggg. The flowers were pollinated by their own pollen. In 2014, out of the seeds obtained after self-pollinating were cultivated and grown 100 plants. No large flowered plant was found. F1 generation only slightly differed in the flower colour from light to dark pink. Four plants were used as maternal component (marked 2000 / 1 4). As a paternal component was used component KO1, which is used in production of current commercial varieties. It is a large flowered diploid with genotype GG, white colour, fimbriata type. Figure 1 represents the difference in size and colour of parental components and triploid hybrid. Maternal plants were emasculated. 30 flowers of every maternal plant were pollinated by pollen from KO1 plants. Seeds from this crossing, were sown in According to the size and shape of a flower, triploid plants were identified. Ploidy testing was carried out on the device Partec PA II with mercury UV lamp in flow cytometry in the Institute of Botany AS CR Pruhonice (Otto 1990, Doležel et al. 1994, Doležel et al. 2007). Triploid plants were planted in pots with a diameter of 12 cm. In July 2015, the diameter of the flower (30 pieces) and plant height were measured. Plants were described using the descriptor used in the breeding station (Černý 1974). The best plants were transferred into in vitro gene bank (Šedivá 2009) to prevent accidental loss of genotypes or infection by viruses. The aim of this experiment was to confirm the possibility of making Petunia triploid plants with genotype Ggg by crossing tetraploid and diploid components. The task was also to investigate the frequency of triploids in F1generation. The third task was to determine the expression of G allele in genotype of triploid Ggg. To do so, the flower size of parental plants and triploid hybrid was compared. Table 1 Crossing in year 2014 Pair Maternal component Ploidy n Paternal component Ploidy n Number of plants in F1 generation Number of triploids / 1 4 KO / 2 4 KO / 3 4 KO / 4 4 KO RESULTS AND DISCUSSION The aim of this experiment was to verify the possibility of making triploid varieties of Petunia hybrida and evaluate some of their features. These varieties would be reproduced vegetatively. F1 hybrid triploid varieties are used with success in some ornamental plants (Reimann-Philipp 1969). For example, in Begonia semperflorens this crossing scheme creates powerful and resistant hybrids. Another advantage is also so called self-cleaning ability. In seed pods of triploid plant, the seeds are not developed, therefore they fall down after several days. The plant is not burdened by the formation of the seeds and blooms continuously until the end of the growing season. In Petunia hybrida is however the crossing between diploid and tetraploid lines not successful, so that this scheme can t be used to produce hybrid varieties propagated by seed. As stated Seidel (Seidel 1962), only when crossed tetraploid maternal component and diploid paternal component, a small number of triploids could be obtained. This corresponds with results of our experiment, as shown in Table 1. Out of the 120 pollinated flowers 10 triploid plants were received. The total number of plants in the F1 generation was 168, but the 158 cases were not regular types, which happened by transferring pollen from other plants. Such plants were very similar to maternal plants, therefore, they varied in shades of pink and had small flower. So on average one triploid plant is received out of 12 pollinated flowers. Normally, in one seed pod of tetraploid OP variety are several hundred seeds (Anderson 2007). 712 P age

3 Low number of triploids obtained is not a problem, when consider that received triploid plants will be reproduced asexually. Specialized companies supplying horticultural firms with young plants are able to produce rooted cuttings in sufficient amount. The advantage of vegetatively propagated varieties is rapid development and change of assortment (Dole and Gibson 2006). Triploid hybrids fit this concept well. Our goal was to create a hybrid genotype Ggg. We assumed that one dominant G allele ensures big flowers of the hybrids. This was examined by measuring the diameter of flowers of various acquired triploids. The average size of the flower was 98 mm, which is almost 25% more than the paternal large-flowered component KO1. The flowers looked like OP tetraploid varieties the size and shape were similar. The edge of the flower was fimbriata type, which increases its attractiveness. According to Table 2 there is a statistical significance (p = 0.05) that the flower diameter of all 10 triploid plants is statistically bigger then parental components 2000 and KO1. Table 2 Comparison of flower size (mm) among triploid plants and parental components Mean Group 1 Mean Group 2 t-stat. sv p Units per group 1 Units per group 2 Stand. deviation 1 Stand. deviation 2 F-stat. p Variances KO1 vs. triplo KO1 vs. triplo KO1 vs. triplo KO1 vs. triplo KO1 vs. triplo KO1 vs. triplo KO1 vs. triplo KO1 vs. triplo KO1 vs. triplo KO1 vs. triplo vs. triplo vs. triplo vs. triplo vs. triplo vs. triplo vs. triplo vs. triplo vs. triplo vs. triplo vs. triplo Note: T-test for independent samples; p statistics p = 0.05; measures in mm; computed in STATISTICS 12. Some plants of tetraploid OP varieties have a flower diameter up to 160 mm. The problem with these varieties is that they usually very differ in flower size. Some plants also have deformed flowers. Plant habit also does not fulfil the requirements of the growers, as the plants are high and don t spread. These OP varieties are suitable for flower lovers and are sold in pictorial packages in the hobby market, but not for professional producers of flowers (Sink 1984). Based on the results we can say that triploid Petunia varieties with genotype Ggg is a good way of breading and producing new commercial varieties. 713 P age

4 Figure 1 Flowers of parental plants and triploid hybrid A) Maternal plant 2000 / 1 B) Paternal plant KO1 C) Triploid plant TRIPLO1 CONCLUSION Flower lovers and growers anxiously wait for new attractive varieties of ornamental plants. Petunia assortment is very broad and coming up with something new is difficult. Producing triploid varieties is still untapped opportunity to enrich the product range. In our work, we have demonstrated that triploid hybrids with genotype Ggg can successfully accomplish this task. The breeding cycle of such varieties is relatively short, and financially and technically not demanding. Triploids obtained in this experiment have attractive flowers and good growth characteristics. ACKNOWLEDGEMENTS The research was financially supported by the breeding company Černý-BioPro Ltd., Prague, Czech Republic. REFERENCES Anderson, N. O Flower Breeding and Genetics: Issues, Challenges and Opportunities for the 21st Century. 1 st ed., Dordrecht, Netherlands: Springer. Ball, V The Ball RedBook. 15 th ed., West Chicago, USA: Geo. J. Ball Publishing. Černý, J Klasifikátor Petunia hybrida. 2 nd ed., Jaroměř: Sempra o.p. Praha. Cornu, A., Maizonnier, D., Wiering, H., de Vlaming, P Petunia genetics. III The linkage group of chromosome V. Annals Amelior Plant, 30(4): Dole, J. M., Gibson, J. L Cutting propagation. 1 st ed., Batavia, USA: Ball Publishing. Doležel, J., Greilhuber, J., Suda, J Flow cytometry with plant cells: Analysis of genes, chromosomes and genomes. 1 st ed., Weinheim, Germany: Wiley-VCH Verlag GmbH. Doležel, J., Lucretti, S., Schubert, I Plant chromosome analysis and sorting by flow cytometry. Critical Review Plant Science, 13(3): Gerats, T., Strommer, J Petunia: Evolutionary, Developmental and Physiological Genetics. 1 st ed., New York, USA: Springer. Maatsch, R., Nolting, G Registrierung des Sortimentes von Petunia x hybrid Vilm. Gartenbauwissen, 33(4): Matsuda, H Cytological studies of genus Petunia. Cytologia, 6(4): Murphy, D. J Plant Breeding and Biotechnology. 1 st ed., New York, USA: Cambridge University Press. Otto, F DAPI staining of fixed cells for high-resolution flow cytometry of nuclear DNA. Methods in Cell Biology, 33(1): Plickert, K Die Züchtung der grossblütigen superbissima-petunien. Zuechter, 8(3): P age

5 Reimann-Philipp, R Die Züchtung der Blumen. 1 st ed., Berlin, Germany: Paul Parey. Seidel, H Beiträge zur Genetic und Züchtung der tetraploiden Superbissima-Petunia (Petunia x hybrida Vilm. Superbissima group). Zeitschrift Pflanzenzuecht, 48(4): Sink, K. C Petunia. 1 st ed., Berlin, Germany: Springer-Verlag. Šedivá, J Shrnutí poznatků při udržování kolekcí vybraných druhů květin s využitím in vitro technik. Acta Pruhoniciana, 93(1): P age