In order to increase the tolerance and yield safety of sunflower against environmental stresses, the experimental plants were treated with 0.1% suspension of two hormone producing microalgae strains. The aim of the present research was to determine the optimum spraying time of sunflowers with microalgae suspensions. Trials were set up in the Faculty Farm in 2012 in Mosonmagyaróvár. Sunflower (Helianthus annus L.) cv. ”Nk Neoma” was treated with MACC-612 Nostoc enthophythum and MACC-430 Tetracystis sp., which originated from the Mosonmagyaróvár Algal Culture Collection (MACC). The first treatment was applied at the 4–6 leaf stage and the second treatment at the rosette growth stage of sunflower growth. Plots were treated with biomass of the MACC-612 and MACC-430 in a dosage of 400 and 700 g ha-1 (in a concentration of 0.1%). The following parameters were recorded: plant height, diameter of head, plate weight, yield (kg ha-1), oil content, and oil yield (kg ha-1). Plants treated with 0.1% microalgal biomass of the strains MACC-612 Nostoc entophytumand MACC-430 Tetracystis sp. had 15% and 13% yield increase compared with the control (3211 kg ha-1), respectively. The yield surplus originated from the significantly larger diameter of head and plate weight. Larger plate diameters resulted in bigger achene weight, which indicated a positive correlation between the two parameters (R2=0.8731). The two microalgae strains significantly increased (16–18%) the oil yield compared to the control plots. The results proved that plant treatment with suspensions of cyanobacteria (3692 kg ha-1) and microalgae (3628 kg ha-1) positively affected the yield of sunflower.

Keywords: organic farming, sunflower, microalgae, cyanobacteria