## 4 Discussion
It was also found that among the tested different algal filtrate concentrations (5.0%, 25%, 50%, and 100%), the best results concerning seedlings' length and weight were obtained for 50% algal filtrate. The stimulatory effects of algal extracts depend not only on application time and frequency of application, but also on their concentration. Lower doses often elicit the best growth responses [4]. The increased germination percentage at low concentrations may be due to the presence of some growth promoting substances such as phytohormones and micronutrients. Higher concentrations of the extracts can inhibit the germination [39]. In the present study, we also examined seed treatment with algal homogenate/filtrate. At present the majority of the research on biostimulants is conducted using foliar applications while little work has been done on biostimulants as seed treatments. [PERSON] et al. (2016) suggests that combiningthe attributes of biostimulants and applying them to seeds via coating may have tremendous potential to enhance early plant growth and development [24]. The seed treatment in our study concerned the use of algal homogenate for seed coating and filtrate for seed soaking. It was found that seed soaking for 1 h with 50% algal filtrate is a better option to increase seedlings' length than seed coating. However, for both seed treatment methods, better results were obtained for soaked and coated seeds than for non-treated seeds. Seed treatment increases the resistance to biotic and abiotic stress, as well as being responsible for growth responses of plants (e.g., improved root and shoot growth) [3]. For example, [PERSON] and [PERSON] (2010) produced seaweed liquid fertilizer from _Ulva fascita_, using a blender followed by a mortar and pestle. Several concentrations were prepared from the initial filtrate: 10%, 25%, and 50%. Fenugreek seeds were soaked for each concentration of aqueous extracts for 1 h. The maximum value of height and weight was recorded for the 50% extract. This extract also influenced positively the photosynthetic pigments' percentage, carbohydrate, proteins, free amino acids, polyphenols, and nitrogen content in the treated plants [20]. Seeds of cow pea soaked with _Sargassum wightii_ and _Caulerpa chemnitzia_ extracts performed better when compared to the water soaked controls and showed improved seedling growth, dry matter, chlorophyll, protein, amino acid, and sugar content [39]. Tomato seeds treated with _Ulva lactuca_ extracts reduced fungus _Fusarium oxysporum_ incidence (resistance to biotic stress) [40], whereas seeds of sweet pepper and aubergine primed with _Cystoseira barbata_ extract were characterized by improved germination even at low temperatures (resistance to abiotic stress) [35]. The application of algal homogenate/filtrate as formulations with biostimulant properties for seed coating/soaking seems to be a promising option for a sustainable agriculture that aims at reducing the use of mineral fertilizers and pesticides. The biostimulant--a natural plant material, being a component of a seed coating blend--could be adopted for organic crop production and may also reduce the need for high levels of N fertilizer since the biostimulant can enhance N uptake efficiency [24]. In the present paper, we also found that the algal products enriched with Zn(II) ions (both filtrate and homogenate), as well as zinc supplied as inorganic salt in the cultivation of radish inhibited its growth. Although zinc is an essential nutrient for plant growth, elevated concentrations can result in growth inhibition and toxicity symptoms [26]. The application of algal products in plant cultivation can not only increase the height and weight of plants, but also their multi-elemental composition. Our experiments revealed that algal filtrate (50%) applied to the soil or foliarly increased the content of some elements, such as: Zn, B, K, Na, Ca, Mg, Mn. This is supported by results presented by [PERSON] et al.