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A major justifi cation for taxonomic and biogeo- graphic research is its assumed ability to predict the presence of traits in a group for which the trait has been observed in only a representative sub- set of the group. Such predictors are regularly used by breeders interested in choosing potential sources of disease and pest resistant germ plasm for cultivar improvement, by genebank managers to organize the collection, and by germplasm collectors planning to gather maximum diver- sity. The present study tests taxonomic and biogeographic associations with 10,738 disease and pest evaluations, derived from the literature and genebank records, of 32 pest and diseases in fi ve classes of organisms (bacteria, fungi, insects, nematodes, and virus). The data show that ratings for only Colorado potato beetle (Lep- tinotarsa decemlineata (Say)) and one pathogen (Potato M Carlavirus) are reliably predicted both by host taxonomy and climatic variables. While it is logical to initially take both taxonomy and geographic origin into account while screening genebank materials for pest and disease resis- tances, such associations will hold for only for a small subset of resistance traits. Based on these results, a more effective strategy than taxonomic and biogeographic prediction is probably careful screening of core collections.

A major justification for taxonomic research is its assumed ability to predict the presence of traits in a group for which the trait has been observed in a representative subset of the group. Taxonomy is regularly used by breeders interested in choosing potential sources of diseaseresistant germplasm for cultivar improvement. We designed this study as an empirical test of prediction by associating resistance to white mold [caused by the fungal pathogen Sclerotinia sclerotiorum (Lib.) de Bary] to diverse potato (Solanum spp.) taxonomies and biogeography, using 144 accessions of 34 wild relatives of potato in Solanum sections Petota and Etuberosum. Tremendous variation for resistance to white mold occurs both within and among species. No consistent association was observed between white mold resistance and taxonomic series (based on a phenetic concept), clades (based on a cladistic concept), ploidy, breeding system, geographic distance, or climate parameters. Species and individual accessions with high proportions of whitemold-resistant plants have been identified in this study, but both often exhibit extensive variation and designation of either as resistant or susceptible must take this variation into account. Therefore, taxonomic relationships and ecogeographic data cannot be reliably used to predict where additional sources of white mold resistance genes will be found.