The evolutionary significance of variation in infection behavior in two species of rust fungi on their hosts and related nonhost plant species

Abstract

We explored the association between the phylogeny of 14 species of beans in the genera Phaseolus and Vigna (subtribe Phaseolinae) and the progress of infections in them caused by two pathogenic rust fungi, Uromyces appendiculatus (Pers.) Unger and Uromyces vignae Barclay. The analyses involved construction of phenograms, ordinations, and cladograms derived from the infection characteristics and their comparison to a composite of three previously published DNA phylogenies. The patterns of infection by U. vignae showed no relationship to the phylogeny of the infected plants. The course of infection by U. appendiculatus, however, displayed a significant phylogenetic component, although the defense responses of the infected plants themselves did not. These differences in phylogenetic signal between infections caused by the two fungi may reflect distinct evolutionary histories with members of the Phaseolinae, a long association for U. appendiculatus but a much more recent one for the more host-specific U. vignae.Key words: bean rust, cowpea rust, evolution, infection characteristics, Phaseolus, Vigna.