The investigation was carried out at the Dobrudzha Agricultural Institute – General Toshevo during 2009-2011.
Twenty fertility restorer lines were used which were crossed with mother line 3A. The obtained 20 hybrid combinations were investigated within a competitive variety testing, using the best and most widely distributed foreign hybrids and the most common Bulgarian hybrid San Luka as standards.
Characters related to productivity were subjected to investigation: seed yield kg/da, percentage compared to the average standard one, oil percentage in the seed, oil yield kg/da, percentage compared to the average standard one.
The resistance of the tested hybrids to downy mildew and the parasite broomrape were also determined.
During the three years of testing the hybrid combinations demonstrated high production potential, the crosses 3A х 68R, 3A х 105R, 3A х 58R showing the best results. The cross 3A х 105R (Velko) is now being for a second year under official variety testing in Romania and is demonstrating very good results. Due to the very good combining ability of this line, the highly productive Clearfield-tolerant hybrid 3А х BTI-R1 was developed, in which a BASF fertility restorer was involved.
When crossed with fertility restorers, line 3A produces very good hybrids which is an evidence for its very good combining ability and makes it especially valuable for breeding aimed at developing sunflower hybrids of a high production potential.