In the years 2009–2011 small-sized tomato plants cv. ‘Bianka F₁’ were sprayed with biostimulators on the basis of marine algae extracts: Acadian (at concentration 0.5%), Bio-algeen S-90 (at 0.5%) and Labimar 10S (at 0.3%). They were used three times: in the stage of 2–3 leaves, before planting and at the beginning of flowering. The aim of study was to evaluate of relationship between tomato yield, cluster features and physiological indices under various seaweed biostimulators. The experiment was carried out in a high plastic tunnel in the Vegetable Experimental Station near Szczecin. Total and marketable yield of tomato sprayed with Acadian and Labimar 10S was increased in comparison the plants treated with preparation Bio-algeen S-90 and the control plants (sprayed with water). All applied preparations had a beneficial influence on the early harvest of tomato fruits, length of clusters and number of fruits in the cluster. Spraying of leaves with Bio-algeen S-90 resulted in a significant increase chlorophyll a, b, a + b and carotenoids content. The applied of Labimar 10S increased of chlorophyll b and a + b level. The higher rate of CO₂ assimilation, larger index of effectiveness of water use in the photosynthesis and no effect stomatal conductance for water and CO₂ concentration in the intercellular pores of leaves were obtained after spraying of tomato with biostimulators. The applied of Labimar 10S and Bio-algeen S-90 decreased the rate of transpiration and significantly increased value of the relative water content index in the tissues of leaves.

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