Transfer of the Kosena Rfk1 gene, required in hybrid seed production, from oilseed rape to turnip rape
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The Ogura cytoplasmic male sterility and fertility restoring (cms/Rf) system is one of the most promising hybrid systems in Brassica species. The Ogura cms has been introduced earlier into spring turnip rape (Brassica rapa L.) and the sterility has been stable. To enable the production of F1 hybrids in turnip rape, the Kosena fertility restoring gene (Rfk1), a homologue of the Ogura fertility restoring gene (Rfo), was transferred from spring oilseed rape (Brassica napus L.) into spring turnip rape by the traditional backcross method. The male fertility, measured here as a pollen production, of the F1 hybrids between turnip rape and oilseed rape was good (83%). The transmission rate of the Rfk1 gene during backcrossing was not essentially different between the pollen (35%) and egg (33%) cells. For the selection of homozygous (Rfk1/Rfk1) turnip rape plants, both testcrosses to male sterile (Ogura cms) turnip rape line and TaqMan based real-time qPCR method were used simultaneously. The TaqMan qPCR detection system was good when used for selecting homozygous plants out of heterozygous ones before flowering. This enabled interpollination instead of inbreeding, which is a benefit with cross-pollinating crop species like turnip rape. According to testcross results of the offspring between male sterile line and homozygous (Rfk1/Rfk1) turnip rape plants, 100% fertility was reached. It was a good indication, that turnip rape with Ogura cms can be restored with the Kosena Rfk1 gene. However, during the subsequent selection of homozygous (Rfk1/Rfk1) plants, it was observed that the Rfk1 gene was still unstable in the genome of turnip rape, and thus the Rfk1 gene needs to be stabilized before its full exploitation in commercial hybrid production is possible.
KeywordsTurnip rape Brassica rapa L. Kosena Rfk1 gene Ogura cms TaqMan qPCR
We thank for Dr. Takako Sakai and Dr. Jun Imamura for providing the breeding lines RfA4 and RfA12, and their technical and scientific support in PCR and qPCR analysis. The study was supported by National Emergency Supply Agency, Finnish Ministry of Agriculture and Forestry, Mildola Oy, Maatalouskesko Oy and RaisioYhtymä Oy.
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