Abstract
Hybrid seed production in sugar beet relies on cytoplasmic male sterility (CMS). As time-consuming and laborious test crosses with a CMS tester are necessary to identify maintainer lines, development of a marker-assisted selection method for the rf gene (the nonrestoring allele of restorer-of-fertility locus) is highly desirable for sugar-beet breeding. To develop such a method, we investigated genetic variation at the Rf1 locus, one of two Rf loci known in sugar beet. After HindIII-digestion, genomic DNAs from beet plants known to have a restoring Rf1 allele yielded a range of hybridization patterns on agarose gels, indicating that Rf1 is a multi-allelic locus. However, the hybridization patterns of 22 of 23 maintainer lines were indistinguishable. The nucleotide sequences of the rf1 coding regions of these 22 maintainer lines were found to be identical, confirming that the lines had the same rf1 allele. Two PCR markers were developed that targeted a downstream intergenic sequence and an intron of Rf1. The electrophoretic patterns of both markers indicated multiple Rf1 alleles, one of which, named the dd(L) type, was associated with the maintainer genotype. To test the validity of marker-assisted selection, 147 sugar beet plants were genotyped using these markers. Additionally, the 147 sugar beet plants were crossed with CMS plants to determine whether they possessed the maintainer genotype. Analysis of 5038 F1 offspring showed that 53 % of the dd(L) plants, but none of the plants with other alleles, had the maintainer genotype. Thus, selection for the dd(L) type considerably enriched the proportion of plants with the maintainer genotype.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-013-9854-8) contains supplementary material, which is available to authorized users.
Highlights
Cytoplasmic male sterility (CMS) is an invaluable character for hybrid seed production in many crop species as it can be used to provide seed parents without the need for an emasculation procedure (Schnable and Wise 1998; Hanson and Bentolila 2004; Budar et al 2006; Chase 2007; Kubo et al 2011)
We show that Rf1 is a multi-allelic locus and that the TK-81mm-O-type bvORF20L is predominant in Japanese maintainer lines
NK-198, NK-305, and NK-322 are restorer lines developed by Hokkaido Agricultural Research Center (HARC), National Agriculture and Food Research Organization (NARO), Japan
Summary
Cytoplasmic male sterility (CMS) is an invaluable character for hybrid seed production in many crop species as it can be used to provide seed parents without the need for an emasculation procedure (Schnable and Wise 1998; Hanson and Bentolila 2004; Budar et al 2006; Chase 2007; Kubo et al 2011). CMS in sugar beet (Beta vulgaris L.) was first described by Owen (1942, 1945) who observed that male sterility resulted from the combined action of at least two nuclear genes, termed X and Z ( termed restorer-of-fertility [Rf] genes), and sterilizing cytoplasm (S). Owen proposed that completely malesterile plants have the genotype [S]xxzz, with the other genotype combinations ([S]XXZZ, [S]XXZz, [S]XXzz, [S]XxZZ, [S]XxZz, [S]Xxzz, [S]xxZZ, and [S]xxZz) usually showing a varying degree of pollen fertility (Bosemark 2006). Monogenic pollen fertility restoration has been reported in sugar beet (Theurer 1971; Pillen et al 1993). In addition to these major genes, phenotypic expression may be affected by modifying gene(s) (Hogaboam 1957). Strict selection for the maintainer genotype enables the identification of maintainer lines to produce stable CMS lines (Nielson and Nemazi 1967; Bosemark 1972)
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