Allozyme polymorphisms in tetraploid potato gene pools and the effect on human selection

The need for broadening a crop's genetic base may be determined by comparin g allele frequencies within the gene pools of farmer selections in their ce nters of diversity with that of modern breeding populations. The genetic st ructure of Andean and Chilean potato farmer selections was investigated wit h the aid of nine isozymes, which have been studied in detail and used to c haracterize North American cultivars and advanced breeding lines. These iso zymes are associated with the most-important agronomic or quality character s in the North American gene pool. By comparing these data with previous an alyses of the North American gene pool, allozyme frequency changes for nine loci were monitored. Allozyme frequency changes were not always due to gen etic drift, but resulted also from directional selection of isozyme marker linked quantitative trait loci (QTLs) affecting agronomic or quality charac ters. Changes in allozyme frequency can also occur as a consequence of plei otropy, i.e. the isozyme itself may be involved in the expression of a phen otype. These allozyme frequency changes may reflect the manipulation of the potato genome by breeders. There were allozymes in some North American cul tivars that were not observed in the farmer selections from the Andes and C hile. This confirms that breeders have already introgressed exotic genes fr om wild and other primitive cultivated tuber-bearing Solanum species. On th is basis, the need for broadening the genetic base for specific chromosomes (or chromosome regions) should be based on analysis with these and other g enetic markers available in potato.