Microsatellite Marker Fingerprinting Reveals Paternity Predicament in Pear Rootstocks

Early in the 20th century, a collection of fire blight resistant pears from around the world was assembled in southern Oregon in efforts to develop improved rootstocks. ‘Old Home’ and ‘Farmingdale’ are two cultivars from Illinois that exhibited fire blight resistance and useful horticultural traits. Both became important as interstem stocks and as parents in the development of new rootstocks. In the 1950s, an Oregon nurseryman collected seed from an ‘Old Home’ tree in British Columbia pollinated by ‘Farmingdale’ and hundreds of numbered selections of this cross ‘Old Home’ x ‘Farmingdale’ (OHxF) were evaluated. Several OHxF selections are now used as rootstocks worldwide, and 45 unique OHxF selections are maintained at the USDA-ARS National Clonal Germplasm Repository (NCGR), in Corvallis, Oregon. Simple Sequence Repeat (SSR) or microsatellite-based profiles were generated for ‘Old Home’, ‘Farmingdale’, 8 OHxF selections, and standard pear cultivars at NCGR using a standard fingerprinting set developed by the European Cooperative Programme for Plant Genetic Resources. ‘Farmingdale’ is thought to be a seedling of ‘Beurré d’Anjou’, and shared at least one SSR allele at each locus tested, confirming this parental relationship. All OHxF selections shared an allele with ‘Old Home’ at each locus, with one allele carrying a suspected pair of base deletions. However, based on the SSR results, it is impossible for ‘Farmingdale’ to be the pollen parent for any of the OHxF selections examined. Evaluation of the world pear collection at NCGR with this fingerprinting set will help identify the actual pollen parent of these rootstocks.