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Genetic research into the heredity of persistence (secondary dormancy)

(2008 – 2011) University of Göttingen, Department of Crop Sciences, Plant-Breeding Unit, Göttingen

Topic

Rape seeds can survive for a long time in the soil, and often do not germinate until years later, appearing as volunteer plants in the following crops. If genetically modified oilseed rape is grown, it can lead to the undesirable mixing of GM rape in subsequent conventional rape crops.

The aim of this project was to investigate the heredity of the persistence tendency (secondary dormancy) in winter rape in order to enable varieties with lower secondary dormancy to be bred. The influence of environmental factors and possible connections to valuable seed substances will be quantified. In order to accelerate the breeding process and to select specifically for the secondary dormancy trait, the project developed molecular markers and provide appropriate genotypes for cultivar breeding.

Summary

Great variation and high heredity for the secondary dormancy trait were observed in the double Haploid winter rape population investigated. Since this trait correlates closely with seed germinability, selecting seeds with high germinability could lead to varieties with a low secondary dormancy tendency. However, a graph of the correlation in the test population showed an unusual distribution, so selecting for high germinability would lead to genotypes with lower dormancy only to a limited extent. No correlations to other seed characteristics were found.

When combined with linked markers, the quantitative trait loci (QTL) identified can be used to carry out marker-assisted selection for the secondary dormancy trait.

Experiment description

Genotype variation of the secondary dormancy trait

The genetic variation of the secondary dormancy trait was investigated in the seeds of a double haploid oilseed rape population produced by crossing genotypes with high and low secondary dormancy. Since the seeds’ ability to develop secondary dormancy may be linked to other seed characteristics, one aim of the project was to measure the levels of various substances in the seeds. The investigation looked at storage proteins, plant hormones and other seed substances, including the fatty acid composition. In addition, the seed size was calculated using the thousand-seed weight (TSW).

If a close correlation were to be established between the secondary dormancy trait and one or more of the listed seed characteristics, it could make it easier to carry out selective breeding for low expression of the secondary dormancy trait.

Field trials at several sites

229 lines of a double haploid rape population were examined for secondary dormancy and plant substances in field trials. The lines were grown at two sites (Göttingen and Thüle) over the course of two years (2008/2009 and 2009/2010). The seeds were examined for the following characteristics:

  • Secondary dormancy: A laboratory test developed at the University of Hohenheim was used on freshly harvested material to examine the seeds’ ability to develop secondary dormancy. At the start of the test, the rape seeds went through a two-week phase intended to trigger dormancy. The seeds were then tested for germinability.
  • Seed substances: Storage proteins, plant hormones and other seed substances were identified using various analysis methods.
  • Seed weight: The thousand-seed weight was measured.

QTL (quantitative trait loci) analysis

To enable molecular genetic mapping of the secondary dormancy trait, the information obtained from two locations over two years was analysed statistically in terms of dormancy, phenological characteristics and the seed characteristics mentioned above, and integrated into a molecular marker map. QTL analysis makes it possible to identify various gene loci on the marker map that contribute to quantitative trait expression.

The project is part of the joint project on “Developing and testing confinement strategies for oilseed rape”. The network partners - the University of Hohenheim, the University of Göttingen and the Julius Kühn-Institut (JKI) - are collaborating on laboratory analyses, the use of trial fields and data exchange for modelling.

Results

Harvest samples were taken from the double haploid lines in both years of the field trial. Investigations showed great variation for these lines in the expression of the secondary dormancy trait. Genotypes with pronounced secondary dormancy were found to have a lower germination ability. In addition, heredity for the secondary dormancy trait was high.

However, a graph of the correlation with seed germinability in the test population showed an unusual distribution, so selecting for high germinability would lead to genotypes with lower dormancy only to a limited extent.

No other correlations with the dormancy trait were found.

The QTL analysis based on the secondary dormancy data for two years identified five QTLs on a total of five linkage groups. In total, this accounted for 41 per cent of the phenotypic variation.