Cytoplasmic male sterility in sunflower


If transgenic sunflowers are ever grown in Europe, methods for preventing unwanted out-crossing could facilitate co-existence on the farm. This project aims to evaluate the reliability of cytoplasmic male sterility (CMS) in sunflowers to prevent the flow of transgenic pollen.


Assessment of the impact of distance on the rate of pollination

The commercial production of hybrid sunflower seeds requires CMS sunflower lines to be planted near male fertile ones acting as pollen donors. In such cases, all seeds set by male sterile sunflowers theoretically should have been fertilised by a male fertile plant. Field tests in Bulgaria were carried out based on parallel cultivation of four isunflower CMS lines, sown at distances of 10 metres, 1.0 kilometre and 1.5 kilometres from a male fertile donor line. The formation of seeds at different distances was estimated by counting the number of full seeds per sunflower head. Since sunflowers are pollinated by bees, the source of the contributed  pollen must be determined. This was achieved through microsatellite parentage analysis, i.e., by comparing the DNA pattern of hybrid seeds with that of their putative parents: CMS lines and the male fertile line.

Assessment of stability of sterility of different CMS lines under the varying climatic conditions.

In two districts in Bulgaria with correspondingly different climatic conditions, two identical field trials were performed. Seventeen sunflower CMS lines, differing in respect to the origin of cytoplasm and to putative CMS stability, were characterised in respect to genetic authenticity, homogeneity, type of cytoplasm, formation, release and viability of pollen, formation of seeds, and the parentage of seeds.

When the extent of pollen flow is better understood, researchers will suggest practices for using CMS to prevent the spread of transgenes from sunflowers.


The results obtained during the first year of research showed 75 percent decrease of the rate of pollination at a distance of 1 kilometre, and 30 percent decrease at a distance of 1.5 kilometres from the male fertile line. This discrepancy may be explained by the instability of sterility which was observed in the four CMS lines investigated. A microsatellite parentage analysis proved that the male fertile line contributed to the formation of most of the hybrid seeds at distances of 10 metres, 1.0 kilometre and 1.5 kilometres. However, individual seeds were also detected as the result of self-pollination of maternal CMS lines, as well as of cross-pollination between them.

Parentage analysis of hybrid seeds (1-8) obtained at 4 CMS lines (9-12). Male fertile line (13). Enumeration from left to right.
Parentage analysis of hybrid seeds (1-8) obtained at 4 CMS lines (9-12). Male fertile line (13). Enumeration from left to right.

Further experiments were conducted in the second year of research, aimed at investigating the degree of instability of CMS, and at identifying factors affecting the CMS trait in sunflowers. In order to select stable CMS lines for further investigation, research was directed at determining the genetic authenticity and homogeneity of 17 CMS lines and at specifying the identity of plants which release pollen and form seeds.

The research team soon will be releasing a report on the findings from the first growing season.

More information:

Public Deliverables of the Co-Extra project


Atanas Atanassov / Tzvetanka Hvarleva
AgroBioInstitute (ABI), Bulgaria