Submitted to: Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/7/2008
Publication Date: 4/25/2008
Citation: Feng, J., Jan, C.C. 2008. Introgression and molecular tagging of Rf4, a new male fertility restoration gene from wild sunflower Helianthus maximiliani L. Theoretical and Applied Genetics. 117:241-249. Interpretive Summary: To broaden the genetic base and reduce the vulnerability of the cultivated sunflower to diseases and environmental stress, identification of new CMS sources and the associated restorers has been a continuous objective for sunflower researchers. Characterization and molecular mapping of the fertility restoration genes was conducted only for the fertility restoration gene Rf1 of CMS PET1, which is extensively used in the hybrid sunflower production. A newly identified CMS GIG2 was shown to be different from CMS PET1, and represents a new source of male-sterile cytoplasm. More importantly, a single dominant fertility restoration gene Rf4 was derived from a diploid perennial wild species H. maximiliani 1631, which can efficiently restore the male fertility of CMS GIG2. Molecular markers tightly linked to the Rf4 gene have been developed. These markers will effectively assist breeders to identify male-fertile plants and facilitate the development of restorer lines.
Technical Abstract: In sunflower, CMS PET1 and the associated fertility restoration gene Rf1 is the only source extensively used in commercial hybrid production. The search for new cytoplasmic male sterility (CMS) and restorer sources to broaden the genetic diversity is needed to insure efficient hybrid seed production. A new CMS source, CMG GIG2, was identified among progeny of an interspecific hybrid of perennial wild species Helianthus giganteus x HA 89. A corresponding restorer gene was identified from an interspecific amphiploid of HA 89 x H. maximiliani, and was introduced into cultivated background through backcrosses with HA 89. Based on the reactions to a standard set of fertility restoration testers, this new CMS is different from CMS sources previously identified, and is also different from another CMS source from H. gigateus, CMS GIG1. Analysis of 113 F2 individuals from the cross H. giganteus/7*HA 89/3/H. giganteus/ 6* HA 89// H. maximiliani (amphiploid) indicated a single dominant gene conferring complete fertility restoration of the CMS GIG2 cytoplasm. This single dominant gene Rf4 was mapped on the linkage group 3 of public SSR genetic map using SSR and RFLP-derived STS markers. Two co-dominant SSR markers ORS13 and ORS1114 co-segregated with the Rf4 locus, while STS10B1 and ORS822-3 were located on the same side at a distance of 3.1 cM and 31.7 cM, respectively. Furthermore, using an enlarged 933 F2 and F2:3 populations, Rf4 was mapped to 0.9 cM from the SSR marker ORS1114. The new system, consisting of CMS GIG2 and restorer gene Rf4, combined with tightly linked co-dominant SSR marker will facilitate the marker-assisted selection in sunflower hybrid breeding and map-based cloning of the Rf4 gene.