Using microsatellites, isozymes and AFLPs to evaluate genetic diversity and redundancy in the cassava core collection and to assess the usefulness ofDNA-based markers to maintain germplasm collections

The cassava core collection was selected to represent, with minimum repetit iveness, the potential genetic diversity of the crop. The core (630 accessi ons) was chosen from the base collection (over 5500 accessions) on the basi s of diversity of origin (country and geographic), morphology, isozyme patt erns and specific agronomic criteria. To asses the genetic diversity of the core, 521 accessions were typed with four microsatellite loci. Allele dive rsity and frequency, and size variance of dinucleotide repeats (Rst statist ic) were estimated. Microsatellite allele numbers and frequencies varied am ong countries: Colombia and Brazil had the largest number of different alle les across all loci. Mexico also had a high number, ranking fifth after Per u, Costa Rica and Venezuela (which tied). Unique alleles were present in ac cessions from Brazil, Colombia, Guatemala, Venezuela and Paraguay. A small number (1.34%) of potential duplicates were identified through isozyme and AFLP profiles. Thus, the present results indicated that traditional markers have been highly effective at selecting unique genotypes for the core. Fut ure selections of cassava germplasm sets can be aided by DNA-based markers to ensure genetically representative, non-redundant samples.