RAPD markers on seed bulks efficiently assess the genetic diversity of a Brassica oleracea L-collection

The concept of a core collection was elaborated to fit the necessity of opt imizing the management, for both conservation and use, of genetic resources in sizeable collections. This approach requires an analysis of how the gen etic variability is structured among the accessions. The large number of he terogeneous populations in our collection of Brassica oleracea makes geneti c diversity studies based on plant-to-plant analysis impracticable. To over come this limitation, the variability analysis by RAPD on seed bulks was in vestigated for its efficiency in assessing the structure of the genetic div ersity of this collection. The optimal bulk size and the bulking or samplin g variation were evaluated with bulks of different size and with replicated samples. A mixture of known genotypes was also used to characterise the ba nd detection in bulks, and to compare the plant-to-plant and the bulk metho ds. Forty seeds were chosen to represent each population. In such a bulk, t he detection of bands depended on the proportion of the genotype they were derived from in the mixture. Intense and frequent bands were detected in th e bulk with a 15% detection limit. The observed bulking or sampling variati on within populations was smaller than the variation between populations, l eading to an efficient separation of populations with a clustering of all s amples of the same population. The distances calculated from bulk data were highly correlated with the distances based on the plant-to-plant analysis. We demonstrated that RAPD on seed bulks can be used to describe the geneti c diversity between populations.