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Phylogenetic Analysis of Verticillium dahliae Vegetative Compatibility Groups

First and second authors: Instituto de Agricultura Sostenible (IAS), Consejo Superior de Investigaciones Científicas (CSIC), Apartado 4084, 14080 Córdoba, Spain; third and fourth authors: IAS-CSIC and Escuela Técnica Superior de Ingenieros Agrónomos y Montes, Universidad de Córdoba, Edificio C-4 ‘Celestino Mutis’, Campus de Rabanales, Ctra. Madrid-Cádiz, km 396, 14071 Córdoba, Spain.

The evolutionary relationships among Verticillium dahliae vegetative compatibility (VCG) subgroups VCG1A, VCG1B, VCG2A, VCG2B, VCG4A, VCG4B, and VCG6 were investigated by parsimony analysis of amplified fragment length polymorphism (AFLP) fingerprints and sequences of six DNA regions (actin, β-tubulin, calmodulin, and histone 3 genes, the ITS 1 and 2 regions of the rDNA, and a V. dahliae-specific sequence), using 101 isolates of diverse host and geographic origin. Polymorphisms in gene sequences among isolates of different VCGs were very low and individual gene genealogies provided very little resolution at the VCG level. The combined analysis of all DNA regions differentiated all VCG subgroups except for isolates in VCG1A and VCG1B. VCG clonal lineages in V. dahliae and evolutionary relationships among them were resolved independently by analyses of AFLP fingerprints, multiple gene genealogies, and the combined data set of AFLP fingerprinting and multiple gene genealogies. Two main lineages (I and II) were identified with lineage II comprising two closely related subgroups of VCGs. Lineage I included VCG1A, VCG1B, and VCG2B³³⁴; and lineage II included, VCG2A and VCG4B (subclade 1); and VCG2B⁸²⁴, VCG4A, and VCG6 (subclade 2). VCG subgroups were monophyletic except for VCG2B that appeared polyphyletic. Limiting the parsimony analysis either to AFLP fingerprints or DNA sequences would have obscured intra-VCG differentiation. Therefore, the dual approach represented by the independent and combined analyses of AFLP fingerprints and DNA sequences was a highly valuable method for the identification of phylogenetic relationships at the intraspecific level in V. dahliae.

Additional keywords:defoliating pathotype, genetic diversity, Verticillium wilt.