Increasing the yield safety of modern sunflower hybrids in common production makes it necessary to optimise agrotechnical factors. Sowing technology is able to significantly compensate the unfavourable effect of crop year, as well as to contribute to the more successful protection against pathogens and yield maximisation. Plant number and sowing date are two fundamental issues of agrotechnics. The experiment was established on the Hajdúság loess ridge in 2009. The plant number and sowing date reactions of the sunflower hybrids in common production were examined in relation to pathological factors and productivity. Different sowing dates significantly affected stem rigidity parameters and the level of infection. The extent of lodging and stem breakage under the head was the lowest at the latest sowing date in the average of hybrids (4.6%, 1.9%), whereas the highest values were observed in the case of the early sowing date (9.5%, 6.3%).

The same tendency prevailed in the case of stem Sclerotinia, Diaporthe and head disease infections. Furthermore, increasing plant number also led to worsening stem rigidity parameters and the increasing level of infection by the examined pathogens. In the dry crop year 2009, 55 000 plant ha-1 population density was shown to be optimal (4838 kg ha-1). In 2009, maximum yield (4717 kg ha-1) was obtained in the case of the mid-April sowing date in the average of hybrids. Both earlier or later sowing dates led to yield reduction (3712 kg ha-1, 4228 kg ha-1). The damage caused by pathogens gradually decreased with later sowing dates. The oil content of hybrids was affected by sowing date and population density. The highest average oil content was observed at the 3rd sowing date (44.51%) and the highest examined plant density level (44.27%).

Oil yield was primarily determined by yield. Based on their different genotypes, hybrids reacted differently to the changes of both plant number and sowing date in relation to the examined factors during the experiment.

Keywords: sunflower, sowing date, plant number, yield, oil content