Isozyme analysis of entire and core collections of Solanum tuberosum subspandigena potato cultivars

The International Potato Center (CIP), near Lima, Peru, holds one of the la rgest clonal collections of tetraploid (2n = 4x = 48) Andean farmer selecte d potato cultivars (Solanum tuberosum L, subsp. andigena Hawkes), CIP selec ted a fore collection of 306 Andean cultivars from the 2379 accessions avai lable in the genebank to facilitate the utilization of these genetic resour ces. Our objective was to investigate the genetic structure in both the ent ire collection and its respective core subset with nine isozyme markers tha t have been genetically characterized. Such an analysis provides a means to validate the sampling strategy of the fore collection, Allozyme frequencie s and average heterozygosity were calculated for each locus investigated. T he allozyme frequency distribution for each locus was tested for homogeneit y between the entire and core collections by chi(2) tests. A total of 38 al lozymes were scored in the entire collection. Only two rare allozymes (Idh- 1(3) and Pgi-1(5)) with a gene frequency (q) of 0.0002 (Or 0.02%) were not included in the core collection. The most frequent allozymes in the entire collection also showed the highest frequencies in the core collection. The allozyme frequency distributions were also homogeneous (P > 0.05) for all l oci except for the Pgi-1 and Got-1 loci. Average locus heterozygosity was s imilar (P > 0.05) between the entire and core collection (49 and 50%, respe ctively). This analysis suggests that the sampling strategy to develop this core collection of tetraploid Andean potato cultivars was adequate to capt ure a representative sample of the allozyme loci, because only rare alleles (q < 0.0005 or 0.05%) were lost in the selected core subset. Therefore, th is core collection may be an appropriate entry point for researchers who wi sh to utilize the genetic diversity of this gene pool more efficiently.