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Christian Andreasen, Andrius Hansen Kemezys and Renate Müller

Gerbera hybrida is an ornamental plant of great commercial interest, which is primarily propagated by seeds. We investigated whether increasing fertilizer concentrations during seed set enhanced plant biomass, number of flower heads, seed set, and seed weight. Furthermore, we studied whether an additional foliar calcium application influenced the same parameters. Subsequently, the effect of the various treatments on the germination of the obtained seeds was explored. Two identical experiments (A and B) were carried out with five concentrations of nutrient solutions corresponding to an electrical conductivity (EC) of 1.25 mS·cm−1, 2.50 mS·cm−1, 3.75 mS·cm−1, 5.00 mS·cm−1, and 6.25 mS·cm−1. Additionally, plants were sprayed with a 0.5% foliar-applied calcium solution or deionized water (control) three times during the experimental period. In Expt. A, the concentration of fertilizer significantly affected seed production. Number of flower heads and seed weight were not influenced by the dose of fertilizer, but plant biomass and number of seeds were significantly reduced at the highest concentration (6.25 mS·cm−1). In Expt. B, the fertilizer concentration did not affect number of flower heads and seed number, but seed weight and plant biomass were significantly reduced at the highest fertilizer concentration. In both experiments, the seeds germinated slower and less seeds germinated when plants had received the largest amount of fertilizer (6.25 mS·cm−1). In none of the experiments did applied calcium affect the number of flowers, seed production, seed weight, or the total biomass. Our data indicate that seed producers of G. hybrida should not apply standard fertilizer in a concentration higher than corresponding to an EC of ≈1.25 mS·cm−1. It would have been valuable if we also had included a treatment with a lower EC value like 0.75 mS·cm−1 to improve the estimate of the optimal EC level from a curved function for the seed production and quality parameters.

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Jonas Christensen, Uffe Bjerre Lauridsen, Christian Andreasen and Henrik Lütken

Sea kale (Crambe maritima L.) is a wild edible plant with forgotten and undiscovered potential as a field vegetable. Its natural habitat is gravel beaches in northern Europe and the Black Sea. Three experiments were conducted to find the effect of temperature on seed germination and to determine plant growth response to organic fertilizer and soil types. Germination rates were estimated at three temperatures. Plant growth responses were conducted with application of two fertilizer concentrations [15 and 30 kg plant-available nitrogen (PAN)/ha] and by using four distinct soil types. Seeds sown at 20 and 15 °C reached a significantly greater germination rate after 32 days (48.0% and 40.4%, respectively) than seeds sown at 10 °C (16.6%). The number of days when 50% of the seeds that germinated during the experiment had germinated (T50) were 12.0, 11.8, and 16.8 days for 20, 15, and 10 °C, respectively. Application of 15 or 30 kg·ha−1 PAN did not result in any significant differences in plant size or biomass within 2 months of growth in sandy loam, but substantial plant heterogeneity was observed. Soil composition had a significant effect (P ≤ 0.05) on plant biomass. Plants grown in fine or loamy sand had the greatest growth and biomass. Sea kale seems to have a potential to become a field vegetable, because it grows well on other soil types than gravel. However, domestication processes of the species are required to obtain homogenous plants for future propagation.