Application of Cluster Analysis for Establishment of Genetic Similarity in Gene-For-Gene Host-Parasite Relationships

Genetic similarity and/or dissimilarity among virulence phenotypes of phytopathogenic organisms and generally in gene-for-gene relationships can be exactly expressed by cluster analysis. The present paper deals with the application of a definite hierarchical agglomerative clustering method based on μ-connected clusters as a means for describing genetic structure of virulence in a set of 48 physiological races (isolates) of Bremia lactucae (lettuce downy mildew). A dendrogram and a minimums, panning tree were used to distinguish between virulence phenotypes of B. lactucae. Further application of the methods of numerical taxonomy to phytopathology is briefly discussed.