Triploid Production from Interspecific Crosses of Two Diploid Perennial Helianthus with Diploid Cultivated Sunflower (Helianthus annuus L.).

Wild Helianthus species are a valuable genetic resource for the improvement of cultivated sunflower. We report the discovery and characterization of a unique high frequency production of triploids when cultivated sunflower was pollinated by specific accessions of diploid Helianthus nuttallii T. & G. and H. maximiliani Schr. Genomic in situ hybridization (GISH) analyses indicated that the triploid F1s had two genomes from the wild pollen sources and one from the cultivated line. Mitotic chromosome analyses indicated that the frequency of triploid progenies from the crosses of cultivated lines × H. nuttallii accession 102 (N102) was significantly higher than those of unexpected polyploid progenies from the crosses of wild perennial species × N102, and no unexpected polyploids were obtained from the reverse crosses. Pollen stainability analysis suggested the existence of a low percentage of unreduced (2n) male gametes in some accessions, especially N102 and H. maximiliani accession 1113 (M1113), which were generated at the telophase II and tetrad stages of meiosis. The triploid F1s could be the results of preferred fertilization of the low frequency of 2n male gametes with the female gametes of the cultivated sunflower, due to the dosage factors related to recognition and rejection of foreign pollen during fertilization. The triploids have been used to produce amphiploids and aneuploids. Future studies of the male gametes' fate from pollination through fertilization will further uncover the mechanism of this whole genome transmission. Studies of the genetic control of this trait will facilitate research on sunflower polyploidy speciation and evolution, and the utilization of this trait in sunflower breeding.

Diversifying sunflower germplasm by integration and mapping of a novel male fertility restoration gene.

The combination of a single cytoplasmic male-sterile (CMS) PET-1 and the corresponding fertility restoration (Rf) gene Rf1 is used for commercial hybrid sunflower (Helianthus annuus L., 2n = 34) seed production worldwide. A new CMS line 514A was recently developed with H. tuberosus cytoplasm. However, 33 maintainers and restorers for CMS PET-1 and 20 additional tester lines failed to restore the fertility of CMS 514A. Here, we report the discovery, characterization, and molecular mapping of a novel Rf gene for CMS 514A derived from an amphiploid (Amp H. angustifolius/P 21, 2n = 68). Progeny analysis of the male-fertile (MF) plants (2n = 35) suggested that this gene, designated Rf6, was located on a single alien chromosome. Genomic in situ hybridization (GISH) indicated that Rf6 was on a chromosome with a small segment translocation on the long arm in the MF progenies (2n = 34). Rf6 was mapped to linkage group (LG) 3 of the sunflower SSR map. Eight markers were identified to be linked to this gene, covering a distance of 10.8 cM. Two markers, ORS13 and ORS1114, were only 1.6 cM away from the gene. Severe segregation distortions were observed for both the fertility trait and the linked marker loci, suggesting the possibility of a low frequency of recombination or gamete selection in this region. This study discovered a new CMS/Rf gene system derived from wild species and provided significant insight into the genetic basis of this system. This will diversify the germplasm for sunflower breeding and facilitate understanding of the interaction between the cytoplasm and nuclear genes.

Introgression and molecular tagging of Rf (4), a new male fertility restoration gene from wild sunflower Helianthus maximiliani L.

Cytoplasmic male sterility (CMS) and its fertility restoration (Rf) genes are critical tools for hybrid seed production to utilize heterosis. In sunflower, CMS PET1 and the associated Rf gene Rf (1) is the only source extensively used in commercial hybrid production. The objective of this research was to develop new sources of CMS and fertility restorers to broaden the genetic diversity of hybrid seed production. We identified a new type of CMS, named as CMS GIG2, from an interspecific cross between Helianthus giganteus accession1934 and H. annuus cv. HA 89. Based on reactions to a set of standard Rf testers, CMS GIG2 is different from all previously reported CMS types, including the CMS GIG1 from another H. giganteus accession. We also identified an Rf gene for CMS GIG2 from wild species H. maximiliani accession 1631. The CMS GIG2 and its restoration gene were introduced into HA 89 background through recurrent backcross and single plant selection techniques. Genetic analysis revealed that the CMS GIG2-Rf system is controlled by a completely dominant gene, named as Rf (4), and the gene additive and dominance effects were estimated as 39.9 and 42.2%, respectively, in the HA 89 background. The gene Rf (4) was mapped onto linkage group 3 with simple sequence repeat (SSR) markers and RFLP-derived STS-marker, and is about 0.9 cM away from the SSR marker ORS1114 based on a segregation population of 933 individuals. The CMS GIG2-Rf (4) system tagged by molecular markers provides an alternative genetic source for hybrid breeding in the sunflower crop.