Do We Preserve Unique Apple Germplasm?

In many European countries, preservation of genetic resources in apple is directed mainly, or even exclusively, to so-called heirloom cultivars, i.e., old and presumably indigenous cultivars. However, there is very little information about the extent to which such collections contain a unique and desirable set of genes as opposed to just a random sample of genes from the global population of apple germplasm. Molecular markers, especially Simple Sequence Repeats (SSR), are commonly used for quantification of the amount of diversity in national collections of various plant crops. Provided that the same SSR primers are used and that allele sizing is standardized, data obtained in different studies can be pooled, thus allowing us to estimate not only diversity but also the degree of differentiation among e.g., apple collections preserved in different national gene banks. We have now used primer pairs from a 'standard set', defined by the European Community for Plant Genetic Resources working group on molecular markers, to analyse a total of 144 apple cultivars preserved in Sweden, Finland and Ireland, as well as some other European and non-European cultivars. Preliminary SSR data indicate that the Swedish, Finnish and Irish heirloom cultivars are very diverse. The groups are, however, only slightly differentiated from one another, with the other European cultivars being quite evenly distributed among the cultivars from the three national collections.