Gene genealogies and AFLP analyses in the Fusarium oxysporum complex identify monophyletic and nonmonophyletic formae speciales causing wilt and rot disease

The monophyletic origin of host-specific taxa in the plant-pathogenic Fusar ium oxysporum complex was tested by constructing nuclear and mitochondrial gene genealogies and amplified fragment length polymorphism (AFLP)-based ph ylogenies for 89 strains representing the known genetic and pathogenic dive rsity in 8 formae speciales associated with wilt diseases and root and bulb rot. We included strains from clonal lineages of F. oxysporun f. spp. aspa ragi, dianthi, gladioli, lilii, lini, opuntiarum, spinaciae, and tulipae. P utatively nonpathogenic strains from carnation and lily were included and a reference strain from each of the three main clades identified previously in the F. oxysporum complex; sequences from related species were used as ou tgroups. DNA sequences from the nuclear translation elongation factor 1 alp ha, and the mitochondrial small subunit (mtSSU) ribosomal RNA genes were co mbined for phylogenetic analysis. Strains in vegetative compatibility group s (VCGs) shared identical sequences and AFLP profiles, supporting the monop hyly of the two single-VCG formae speciales, lilii and tulipae. identical g enotypes were also found for the three VCGs in F. oxysporum f. sp. spinacia e. In contrast, multiple evolutionary origins were apparent for F. oxysporu m, f. spp. asparagi, dianthi, gladioli, lini, and opuntiarum, although diff erent VCGs within each of these formae speciales often clustered close toge ther or shared identical EF-1 alpha and mtSSU rDNA haplotypes. Kishino-Hase gawa analyses of constraints forcing the monophyly of these formae speciale s supported the exclusive origin of F. oxysporum f. sp. opuntiarum but not the monophyly of F. oxysporum f. spp. asgaragi, dianthi, gladioli, and lini . Most of the putatively nonpathogenic strains from carnation and lily, rep resenting unique VCGs, were unrelated to F. oxysporum f. spp. dianthi and l ilii, respectively. Putatively nonpathogenic or rot-inducing strains did no t form exclusive groups within the molecular phylogeny. Parsimony analyses of AFLP fingerprint data supported the gene genealogy-based phylogram; howe ver, AFLP-based phylogenies were considerably more homoplasious than the ge ne genealogies. The predictive value of the forma specialis naming system w ithin the F. oxysporum complex is questioned.