OH×F Paternity Perplexes Pear Producers

Abstract

Early in the 20th century, a collection of fire blight resistant pears from around the world was assembled in southern Oregon in an effort to develop improved rootstocks. 'Old Home' and 'Farmingdale' are two cultivars from Illinois that exhibited strong 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 purportedly pollinated by 'Farmingdale' and hundreds of numbered selections of this cross of 'Old Home' × 'Farmingdale' (OH×F) were evaluated. Several OH×F selections are now valued as rootstocks worldwide, and 45 unique OH×F 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 OH×F selections, and several reference 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'. Our study showed that 'Farmingdale' shared at least one SSR allele with 'Anjou' at each locus tested, confirming this parental relationship. Our studies showed that all OH×F selections shared an allele with 'Old Home' at each locus, with one allele carrying a suspected pair of base deletions. However, based on our SSR results, it is impossible for 'Farmingdale' to be the pollen parent for any of the OH×F selections examined. Evaluation of the world pear collection at NCGR with this fingerprinting set established the cultivar 'Bartlett' as the actual pollen parent of these rootstock clones. Fruit and leaf morphology is also consistent with 'Bartlett' and not 'Farmingdale' as a parent of OH×F rootstock selections. The highly fire blight resistant 'Farmingdale' is apparently very under-represented in the pedigrees of current pear rootstocks, and deserves renewed consideration.