The dependence of the size of sunflower seeds on their competition within a plant head

The detailed study of the variability of the seed size of oil varieties and confectionary variety SPK was made. The diversity of the character of the changes in size of the seeds within one head in some sunflower plants was revealed and the differences in this trait between oil varieties and the variety SPK were studied. The role of the ameliorating seed production of variety SPK in the stabilization of the seed size was shown. For the first time it was established that the breeding for the increase of the seed size of sunflower is in fact the breeding for the decrease of their number in the head. It was shown that the differences between oil and confectionary varieties are predetermined long before their filling and can be noticed already during the phase of beginning of flowering by number and size of the flowers.