Genetic Mapping of an Rf Gene to a New Cytoplasmic Male-sterile Sunflower Line

The combination of a cytoplasmic male-sterile (CMS) line and the corresponding fertility restoration (Rf) line is a critical tool in large-scale hybrid seed production of sunflower. A single CMS PET-1, originated from wild Helianthus petiolaris subsp. petiolaris Nutt., and the Rf₁ gene has been widely used since the early 1970s. A new CMS line 514A, derived from H. tuberosus / 7718B, was obtained from a scientific exchange with the Liaoning Academy of Agricultural Sciences, Liaoning, China. The aims of this study were: (1) to identify the Rf gene; (2) to analyze of the genetics of the Rf gene; and (3) to map this gene using two F₂ mapping populations.

Thirty-three maintainer and restorer lines from five countries for CMS PET-1, and 20 tester lines from USDA-ARS-NCSL failed to restore fertility suggesting CMS 514A is different than CMS PET-1. Five tetraploid interspecific amphiploids and one hexaploid Helianthus accession were crossed to CMS 514A, with only one amphiploid of H. angustifolius / P 21 containing the Rf gene. Male-fertile plants with 2n=35 and 2n=34 were obtained after backcrossing. Genetic study suggested that the Rf gene was located on the extra H. angustifolius chromosome. Molecular mapping with SSR and EST-SSR markers located this Rf gene on LG 3 of the public sunflower SSR map, with the closest marker ORS13 at 2.8 cM. This study provides a new CMS/Rf gene system, which will expand the diversity of sunflower germplasm, and help to understand the mechanism of the interaction between cytoplasmic and nuclear genes.