Gerbera species are ornamental plants of considerable economic importance produced in many parts of the world. The genus belongs to the sunflower family (Asteraceae) and is widely used as a potted ornamental plant as cut a flower and less often as a decorative garden plant. Gerbera jamesonii, a perennial herb, was introduced from South Africa into Europe and the United States in the 19th century (Albino-Garduño et al., 2008). From this point, selection and improvement toward better cultivars started and plant breeders have developed lines for cut flower production, potted plants for indoor use, and to a limited extent for bedding and landscape plantings (Carpenter et al., 1995). The domesticated cultivars are frequently derived from a cross between Gerbera jamesonii and another species, Gerbera viridifolia, which is also a native to South Africa. Often F1 hybrids are preferred as a result of their uniformity, vigorous growth, and robustness. Potted Gerbera hybrids have become an important commercial product. Numerous cultivars are marketed varying in flower shape, size, and color. Colors of flowers include white, yellow, orange, red, and pink. The center of the flower is sometimes black. Sometimes flowers can have petals of several different colors (Hansen, 1999).
Gerbera hybrids for potted plant production are predominantly propagated from seeds. Meristem culture is used to some extent in commercial micropropagation laboratories, especially to obtain disease-free plant material. In temperate zones, seed production for Gerbera hybrids must take place in heated glasshouses, but in a subtemperate climate, production may take place in fields or under partly protected field conditions (Dufault et al., 1990). High seed quality and uniform germination in various seed batches are essential for growers of ornamental plants, especially because of increasing automation in sowing practices. Consequently, seed companies are interested in identifying critical factors that influence seed production and determine seed quality, but they are at the same time interested in reducing production costs as much as possible and optimize the use of resources (e.g., fertilizer).
Occasionally seed producers experience big differences in seed set and quality among different batches. Reasons for the differences may be humidity, nutrient or water status as well as climate factors during growth of the mother plants. Climate factors and humidity during pollination may also have an impact on fertilization and subsequent seed set. Little is known about factors influencing Gerbera seed set, storage, and germination (Carpenter et al., 1995). In a greenhouse study, it was demonstrated that fertilizer use in the production of potted Gerbera could be reduced by 50% without a negative impact on leaf area, flower head number and appearance, and total plant total dry weight (Zheng et al., 2004). In a field production study, different levels of nitrogen and potassium fertility did not negatively influence flower size and quality (Dufault et al., 1990). Paradiso et al. (2003) evaluated the response of two Gerbera cultivars to EC level of a nutrient solution on 1-year plants fertigated with two EC values, 1.6 dS·m−1 and 2.4 dS·m−1, at pH 6.0. Flower production increased in plants fertigated with 2.4 dS·m−1 solution compared with those under 1.6 dS·m−1 (+16%) and stem thickness and fresh weight of flowers were higher. Higher EC level increased also nutrient uptake, plant development (+9% in leaf area), and water consumption (+11%). However, there was no information in the studies about how fertilizer levels or composition affects seed set or subsequent germination of the produced seed. In Primula vulgaris, potassium has been identified to have influence on seed quality. Increasing seed potassium concentration was negatively correlated with germination capacity in randomly selected batches of commercial seeds (Zerche et al., 2007). Additionally, calcium appears to be a determinant of seed quality. Foliar-applied calcium can have a positive effect on seed set and quality on some ornamental plant species, e.g., Indian gooseberry (Emblica officinalis) (Shukla, 2011) and Petunia (Santos et al., 2009).
In the present study we hypothesized that 1) an increase in fertilizer level during seed set of Gerbera hybrida results in increasing biomass production and flower head number, improves seed set, and enhances seed weight; 2) an additional foliar calcium application will furthermore increase seed set and enhance seed weight; and 3) an increasing fertilizer level will affect the germination speed and germination percentage. We tested these hypotheses by conducting two independent greenhouse experiments.
Albino-Garduño, R., Zavaleta-Mancera, H.A., Ruiz-Posadas, L.M., Sandoval-Villa, M. & Castillo-Morales, A. 2008 Response of Gerbera to calcium in hydroponics J. Plant Nutr. 31 91 101
Allison, V.J. 2002 Nutrients, arbuscular mycorrhizas and competition interact to influence seed production and germination success in Achillea millefolium Funct. Ecol. 16 742 749
Bliss, R.D., Platt-Aloia, K.A. & Thomson, W.W. 1986 Osmotic sensitivity in relation to salt sensitivity in germinating barley seeds Plant Cell Environ. 9 721 725
Carpenter, W.J., Ostmark, E.R. & Cornell, J.A. 1995 Temperature and seed moisture govern germination and storage of Gerbera seed HortScience 30 98 101
Cwalina-Ambroziak, B., Wierzbowska, J., Damszel, M. & Bowszys, T. 2012 The effect of mineral fertilization on achenes yields and fungal communities isolated from the stem of milk thistle Silybum marianum (L.). Gaertner Acta Scient. Polo. Hort. Cultus 11 157 168
DEG 2001 Standarddyrkningsvejledning for Gerbera jamesonii hybrider (Potte-Gerbera). Dansk Gartneri, Copenhagen, Denmark
Draper, N.R. & Schmidt, H. 1966 Applied linear regression. 2nd Ed. John Wiley and Sons, Inc., New York, NY
Dufault, R.J., Phillip, T.L. & Kelly, J.W. 1990 Nitrogen and potassium fertility and plant populations influence field production of gerbera HortScience 25 1599 1602
ISTA 2011 International rules for seed testing. Germination tests. International Seed Testing Association, Basserdorf, Switzerland
Kaya, M.D., Okc¸u, G., Atak, M., Cikili, Y. & Kolsarici, Ö. 2006 Seed treatments to overcome salt and drought stress during germination in sunflower (Helianthus annuus L.) Eur. J. Agron. 24 291 295
Lecompte, F., Abro, M.A. & Nicot, P.C. 2013 Can plant sugars mediate the effect of nitrogen fertilization on lettuce susceptibility to two necrotrophic pathogens: Botrytis cinerea and Sclerotinia sclerotiorum? Plant Soil 369 387 401
Paradiso, R., De Pascale, S., Aprea, F. & Barbieri, G. 2003 Effect of electrical conductivity levels of nutrient solution on growth, gas exchanges and yield of two Gerbera in soilless system. Proceedings of IS on Greenhouse Salinity. Eds: A. Pardossi et al Acta Hort 609 165 171
Santos, K.M., Fisher, P.R. & Argo, W.R. 2009 Stem versus foliar uptake during propagation of Petunia × hybrida vegetative cuttings HortScience 44 1974 1977
Shukla, A.K. 2011 Effect of foliar application of calcium and boron on growth, productivity and quality of Indian gooseberry (Emblica officinalis) Indian J. Agr. Science 81 628 632
Sonneveld, C., Bass, R., Nijssen, H.M.C. & de Hoog, J. 1999 Salt tolerance of flower crops grown in soilless culture J. Plant Nutr. 22 1033 1048
Steer, B.T., Hocking, P.J., Kortt, A.A. & Roxburgh, C.M. 1984 Nitrogen nutrition of sunflower (Helianthus annuus L.): Yield components, the timing of their establishment and seed characteristics in response to nitrogen supply Field Crops Res. 9 219 236
Zerche, S., Verma, S.S., Ewald, A. & Ludwig-Müller, J. 2007 Quality of Primula vulgaris seeds as related to maturation level, mineral composition, abscisic acid content, storage duration and eluate conductivity Seed Sci. and Tech. 35 111 128
Zheng, Y., Graham, T., Richard, S. & Dixon, M. 2004 Potted Gerbera production in a subirrigation system using low-concentration nutrient solutions HortScience 39 1283 1286