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Resistance

Ordination, A Multivariate Method for Estimating Relative Resistance of Populus tremuloides and Virulence of Hypoxylon mammatum. D. H. Griffin, Department of Environmental and Forest Biology, College of Environmental Science and Forestry, Syracuse, NY 13210; P. D. Manion, Department of Environmental and Forest Biology, College of Environmental Science and Forestry, Syracuse, NY 13210. Phytopathology 76:1289-1293. Accepted for publication 19 May 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-1289.

An ordination technique using modified q-correlations as measures of similarity has been developed and applied to data from virulence testing with Hypoxylon mammatum, the causal agent of a stem canker on Populus tremuloides. The ordination produces linear vectors of the aspen clones or the fungal isolates that are correlated to the underlying measurement variables in a consistent fashion such that one pole of the ordination can be interpreted as representing susceptibility of the clones or low virulence of the isolates, and the opposite pole representing resistance of the clones or high virulence of the isolates. Intermediate positions in the vector represent intermediate levels of resistance or virulence proportional to their distance on the vector. The ordination process can use both quantitative and quantal variables and effectively summarizes the information contained in these variables into a unified scale of resistance or virulence. The complex of data for the host clones or pathogen isolates compared by the ordinations can be dissected to determine how the variables relate to the response gradient. Isolate specific responses of the aspen clones, vertical resistance, were indicated by reversals in the ordinations of the clones by different isolates. Some clones were consistently placed at either the resistant or susceptible ends of the ordination vectors of the various isolates, indicating horizontal resistance mechanisms as well.