Year: 2013
Type: dissertation
Abstract: Spring turnip rape (Brassica rapa ssp. oleifera) is the major oilseed crop cultivated in Finland. The earliness of turnip rape favours its cultivation in northern climates, but its seed yield is low. Hybrid breeding has been utilized in many agricultural crops to improve the seed yield. The exploitation depends on the degree of heterosis that a specific crop shows and on the requirement of a functional hybrid system to cross the parent lines in the production of F1 hybrid seed. In this thesis, the possibility to advance hybrid breeding in developing higher-yielding spring turnip rape cultivars was studied. Spring turnip rape expressed heterosis for increased seed yield. Composite hybrids showed significantly higher yield potential than open-pollinated cultivars. Testing the combining abilities of the parent lines is important in turnip rape. A high degree of variation in commercial heterosis for seed yield was observed between the tested combinations within the groups in both synthetics and composite hybrids. The highest yield increase achieved in this study was 18% in synthetics and 23% in composite hybrids. The Ogu-INRA CMS/Rf hybrid system was selected for the study. To generate a functional, fertility-restoring male line for turnip rape, the Kosena fertility-restoring Rfk1 gene, originating from Japanese radish (Raphanus sativus) and homologue to the Ogura fertility restoring gene Rfo, was transferred successfully from oilseed rape (B. napus) to turnip rape. Transferring of the gene was realized using interspecific crosses followed by traditional backcrossing. The TaqMan qPCR method proved useful in selecting homozygous restorer plants before flowering. Interpollination of selected plants instead of inbreeding is a benefit in cross-pollinating crops that suffer from inbreeding depression. The Rfk1 gene was able to restore the fertility of turnip rape with Ogura CMS, but the trait was unstable in the turnip rape genome. The Rfk1 gene was localized on an additional radish chromosome in the A genome of turnip rape. The BAC64 clone, carrying the Rfo locus, homolog to the Rfk1, identified the locus both in the additional radish chromosome and in the turnip rape chromosome (A09). The high homology of this locus between radish and turnip rape and its location in subterminal part of the chromosome in both genomes would facilitate the transfer of the fertility-restoring trait from radish to turnip rape. It was concluded that additional breeding techniques such as changing the ploidy level or using irradiation to increase the recombination activity between nonhomologous R and A genomes may be required. Even though 100% F1 hybrids were not tested here, the results of this thesis support the use of hybrid breeding in turnip rape. The breeding work towards a stable, fertility-restoring male line for the Ogu-INRA CMS/Rf hybrid system should be continued. To have a functional Ogu-INRA CMS/Rf hybrid system for turnip rape, it seems ideal if the homologous chromosomal area in the A genome could be substituted with the radish chromosome area having the restorer gene.
Source: Työväentutkimus Vuosikirja
Author: Tarja Niemelä
Language: English
Topic: Genetics and Plant Breeding
Subfield: Plant Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2118696955