Genetic variation and inheritance of secondary seed dormancy in winter oilseed rape (Brassica napus L.)

Abstract

Secondary seed dormancy in oilseed rape is a phenomenon that allows seeds to survive in the soil for many years without germination. Following soil cultivation, dormant seeds may germinate in subsequent years and are the reason for the occurrence of volunteer oilseed rape plants in successive crops. These volunteer plants pose a common threat, especially under the assumption of previously cultivated transgenic plant material. Genetic reduction of secondary dormancy in oilseed rape could therefore provide a mean to reduce the frequency of volunteer plants and its subsequent pollen dispersal. However, little is known about the genetic variation for and the environmental influence on the secondary seed dormancy of winter oilseed rape cultivars. Therefore one aim of the present study was to analyse secondary seed dormancy in a set of 28 current winter oilseed rape cultivars tested in 2008/2009 in field experiments at six different locations in Germany. To further investigate the inheritance of this trait a double haploid (DH) winter oilseed rape population consisting 229 genotypes from a cross 'Express 617' x 'R53' was tested for correlations to other seed traits. Field experiments were performed in two consecutive years from 2008/2009 to 2009/2010 at two locations in Germany with two replicates. Seeds harvested from open pollinated plants were used for all analyses, including a laboratory test for secondary dormancy. A previously developed molecular marker map of the DH population was used to map QTL of the relevant traits. In the ANOVA highly significant effects were found for the influence of the locations and for the variation among the genotypes of the 28 winter oilseed rape cultivars. Among these genotypes, secondary seed dormancy ranged from 8% to 56% and the heritability was high (0.97). The means for the six locations ranged from 12% to 38%. The results of the DH-population showed significant effects of the location, the genotypes and their interactions on secondary seed dormancy. Heritability was high (0.85) and secondary dormancy ranged from 5% to 96%. Two major (above 10% of explained phenotypic variance) and three minor (under 10% of explained phenotypic variance) QTL for secondary dormancy were detected which together explained 42% of the phenotypic variance. Secondary dormancy values showed significant negative correlations with the germination rate (-0.71), glucosinolate content (-0.14) and the content of the storage protein Napin (-0.19). Additionally a significant positive correlation between secondary dormancy and the abscisic acid content was revealed (0.14). The large genetic variation and the high heritability indicate that secondary dormancy is a heritable trait and that selection for low secondary dormancy is possible and effective breeding for reduced secondary seed dormancy could be performed.