A major justifi cation for taxonomic and biogeographic 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 subset 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 diversity. he 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 [Leptinotarsa 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 resistances, 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. © Crop Science Society of America.