Quantitative effects of vernalization requirement, day length and temperature on flowering time of oilseed rape

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Vernalization requirement, day length, and temperature are key factors that determine days to flowering in oilseed rape (Brassica napus L.). For winter oilseed rape genotypes, considerable differences in vernalization requirement have been reported and a positive correlation between the degree of vernalization requirement and frost tolerance has been discussed in the literature. Under typical western European growing conditions, the vernalization requirement of winter oilseed rape cultivars is met by end of December - plants transferred from the field to the greenhouse flower readily within short time. However, under field conditions flowering begins only about four months later, indicating that other factors like day-length and/or temperature regulate flowering time. The main objective of the present project is the elucidation of the relationships between vernalization requirement and frost tolerance, respectively winter survival, and flowering time in dependence of day-length and temperature. Therefore a segregating doubled haploid population, derived from a cross between spring-type variety Topas (DH4079) and winter-type oilseed rape Express will be phenotypic characterized (a) for its vernalization requirement and days to flowering under greenhouse conditions, (b) for its frost tolerance as determined after incubating plants in a frost chamber, (c) for the effect of day-length and/or temperature on days to flowering of fully vernalized plants, and (d) for its segregation for winter survival and flowering time in field experiments (sown in August) as well as for its tendency to form inflorescences in the year of sowing for spring sown trials (sown in April). All phenotypic data will be used to map corresponding QTL in a high density molecular marker map of this population on the basis of the Illumina Infinium Brassica 60K SNP Chip technology. QTL analysis will show if QTL for frost tolerance, winter survival and days to flowering obtained under different environmental conditions will collocate or differ in their positions. A complementary high resolution transcriptomic analysis (MACE; Massive Analysis of cDNA Ends) will be performed to identify genes that are differentially expressed in contrasting bulks of early vs. late flowering and in frost sensitive vs. frost tolerant genotypes. cDNA Sequences (100bp) obtained from MACE and the Illumina SNP marker sequences will be used to identify their physical position in the Brassica napus genome and to compare their position with mapped QTL. SNP markers developed by other project partners of this priority program for other genes affecting flowering time in Brassica napus will also be mapped and their position will be compared with QTL detected in the different environments in this project.