Assessing changes in the genetic diversity of potato gene banks .2. In situ vs ex situ

An important question in the conservation of potato germ plasm is whether germ plasm in the gene bank, although stable, still represents the in situ populations from which it was collected, sometimes many decades ago. The answer would direct objective decisions regarding the value of re-collections and in situ preservation. The present study was undertaken as a project of the Association of Potato Inter-gene-bank Collaborators (APIC). It measured genetic differentiation between potato germ plasm maintained in the US gene bank for many years and current in situ populations re-collected from the same original sites in the wild. Solanum jamesii and Solanum fendleri from the United States were used as representatives of potato germ plasm. Re-collections were carried out in 1992 at the same locations at which gene bank-conserved accessions had been collected in 1958 and 1978. RAPD markers revealed significant genetic differences between gene bank-conserved and re-collected in situ populations for all seven comparisons of S. jamesii (diploid outcrosser), and 12 of 16 comparisons within S. fendleri (tetraploid inbreeder). The average genetic similarities were 65.2% for S. jamesii and 80.4% for S. fendleri. Possible explanations and consequences of these unexpectedly large differences are discussed.