Abundance, polymorphism and genetic mapping of microsatellites in oilseed rape (Brassica napus L.)

The objective of the present study was to estimate the abundance and degree of polymorphism of simple sequence repeat (SSR) markers in rapeseed. By sc reening about 45 000 clones of a small inserts library of rapeseed total DN A the abundances of GA/TC and CA/TG simple sequence repeats in the rapeseed genome were estimated to be approximately one repeat every 100 kb and 400 kb, respectively. After sequencing 13 positive clones, primer pairs could b e designed for 11 microsatellite loci. Seven of these primer pairs produced reproducible amplification products in a set of 31 rapeseed genotypes, wit h one pair amplifying two independent products, giving a total of eight amp lified loci. The different microsatellite loci displayed between one and th ree visible alleles. At four loci, additional null alleles were observed. W ith up to four alleles, polymorphic microsatellite markers show significant ly higher allele numbers in rapeseed than restriction fragment length polym orphism (RFLP) markers. Four of the eight microsatellite markers could be m apped on four different linkage groups of an RFLP map of the rapeseed genom e.