Genome Mapping for Development
of Improved Rapeseed (Brassica napus) Varieties
Using Molecular Markers

Rapeseed (Brassica napus L.) is an important source of edible oil in many countries. In Egypt, it was introduced as an oil crop to be cultivated in newly reclaimed land. The development of a new crop generally requires the development of cultivars which possess desirable agronomic characters so that they produce a high yielding usable product. Genetic maps are of potential utilization in plant breeding and plant improvement programs as well as in studies of genome evolution, organization and manipulation. However, genome mapping depends on the availability of markers. Molecular biology has provided different types of useful markers, among them RFLPs (Restriction Fragment Length Polymorphism) and RAPDs (Random Amplified Polymorphic DNA). These markers have revolutionized the ease at which maps can be generated. Applications of molecular markers for crop plant improvement and plant biology stem from the association of markers with genes controlling traits of agronomic interest.

•  Assembling germplasm from national and international sources.

•  Screening for RFLPs among germplasm resources using P32 radioactive and non-radioactive detection methods.

•  Screening for RAPD markers among germplasm.

•  Detection of polymorphism in fragments containing highly repeated sequences.

•  Sexual hybridization between parental lines, containing targeted traits.

•  Generation of F2 segregating population.

•  Analysis of linkage relationships among molecular markers (RFLPs and RAPDs) using statistical procedures and the Mapmaker computer program.

•  Linkage analysis between traits of economic importance and molecular markers and demonstration that such linkages are sufficiently tight to use the molecular markers as indirect selection criteria for the trait of interest.

•  Develop a comprehensive genetic map using morphological, biochemical and molecular markers.

ACHIEVEMENTS

•  A genomic library was generated by the methylation sensitive restriction enzyme PstI.

•  RFLP markers were identified among 13 B. napus accessions using probes derived from the genomic library and with different probe/enzyme combinations.

•  RAPD markers were detected among the B. napus accessions.

•  Genetic variability was studied using RFLP and RAPD analysis and a dendrogram was constructed using UPGMA method to illustrate the phylogenetic relationships among these accessions.

•  Based on genetic variability revealed by RFLPs, RAPDs, isozymes erucic acid content and morphological markers, parental varieties were chosen and crossed to generate F2 segregating population for mapping.

•  Using the Mapmaker computer program a RAPD-based map has been constructed for B. napus and currently additional RFLP and RAPD markers are being added to saturate the map.