Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 1, 2008
Publication Date: June 1, 2008
Citation: Jansky, S.H., Simon, R., Spooner, D.M. 2008. A Test of Taxonomic Predictivity: Resistance to Early Blight in Wild Relatives of Cultivated Potato. Phytopathology. 98(6):680-687. Interpretive Summary: Taxonomy is the theory and practice of describing, naming, and classifying organisms into related groups. Taxonomy has many uses, but perhaps one of the most useful is to serve as a predictive tool. That is, it is assumed that related organisms share traits, and breeders interested in choosing potential sources of disease resistant plants use taxonomy as a guide. This study was designed to test this prediction idea by associating disease resistance of wild potatoes to a fungus called early blight. We also tested associations of potato taxonomy to biogeography, with the potential that closely spaced populations or populations sharing habitats shared disease resistances. No consistent association was observed between early blight resistance and taxonomy or biogeography. Although we did find some species or individual populations that generally had high resistance to early blight, variation in these populations or species reduced the prediction of overall resistance. This study is useful because it alerts breeders interested in early blight resistance that taxonomy and biogeography have limitations in planning their breeding work.
Technical Abstract: Early blight (caused by the foliar fungus Alternaria solani) is a widespread disease that appears annually in potato crops worldwide. This is our second study of a disease resistance in wild potatoes to test the assumed ability of taxonomy to predict the presence of traits in a group for which the trait has been observed in a representative subset of the group; we also tested associations to ploidy, crossing groups, and geography. As in our prior study of Sclerotinia sclerotiorum (white mold) resistance, tremendous variation for resistance to early blight occurs both within and among species, and to taxonomic series (based on an intuitive interpretation of morphological data), clades (based on a cladistic analysis of plastid DNA data), ploidy, breeding systems, geographic distance, and climate parameters. Species and individual accessions with high proportions of early blight resistant plants were identified in our study, but typically exhibited extensive variation. Consequently, designation of species or accessions as resistant or susceptible must take this variation into account. Therefore, taxonomic relationships and ecogeographic data cannot be used as reliable predictors of where additional sources of early blight resistance genes will be found.