The investigation was carried out at Dobrudzha Agricultural Institute – General Toshevo (DAI) in 2004 and 2005. The investigation included 24 fertility maintainer sunflower lines (B-lines) developed at DAI. To shorten the process of developing sterile analogs of the B-lines included in the study, embryo cultivation was used. Immature embryos 12-16 days old were isolated from 24 crosses of A x B type made under field conditions in 2004. Twenty-five embryos were plated from
each cross. In parallel, 20 seeds from each B-line were sown in a greenhouse to ensure the back-cross.
The formed young plants (AB) were transferred to soil and grown under greenhouse conditions. During flowering, the AB plants from each variant were pollinated with the respective B-line to realize back-cross 1(BC1). Out of the 24 variants (AB x B), 630 BC1 immature embryos were obtained, 320 of which were cultivated in vitro till formation of young plantlets. The plants were grown in a greenhouse till flowering, when second back-cross was made (BC2). A total of 188 BC2 embryos were produced, with different distribution by variants. The cycle was repeated till realizing BC3. A total of 131 BC3 seeds were produced, which were planted under field conditions and a fourth back-cross was carried out. By applying this approach, the process of developing sterile analogs of B-lines was shortened by 3 years.