Phytoparasitica (1999) 27 (1) - Phylogeny of VCGs and formae ...
R.P. Baayen, K. O'Donnell, C. Waalwijk, P.J.M. Bonants, E. Cigelnik and E.J.A. Roebroeck (1999)
Phylogeny of VCGs and formae speciales of Fusarium oxysporum and F. redolens
Phytoparasitica 27 (1)
Workshop on Genetic Aspects of Fusarium oxysporum and Related Species, Jerusalem, Israel
Abstract: Fusarium oxysporum is divided into formae speciales, races, and clonal lineages (vegetative compatibility groups, VCGs). Knowledge of the phylogenetic relationships among such entities is essential for developing proper diagnostic tools as well as for predicting the pathogenic behavior and potential of strains. By comparing nuclear (EF-1-alpha) and mitochondrial (mtSSU rDNA) sequences, O'Donnell et al. (1998) were able to demonstrate that F. oxysporum comprises three major clades. Isolates of F. oxysporum f.sp. cubense fell into five phylogenetically distinct lineages within two of the three major clades. The present study was undertaken to test whether other formae speciales also consist of fungi with independent evolutionary origins. EF-1-alpha and mtSSU rDNA sequences were analyzed for F. oxysporum ff.spp. dianthi, gladioli, lilii, tulipae and opuntiarum, as well as for a number of nonpathogenic isolates. Among this series, members were found of all three major clades. Only a single nonpathogenic isolate from lily fell in major clade 1. Clade 2 comprised F. oxysporum f.sp. dianthi, f.sp. lilii, and three VCGs of f.sp. gladioli. Clade 3 comprised F. oxysporum f.sp. tulipae, f.sp. opuntiarum, and three other VCGs of f.sp. gladioli. Biocontrol strains from carnation were not related in anyway to f.sp. dianthi, nor were nonpathogenic isolates from lily related to f.sp. lilii. AFLP analyses supported the distinction of F. oxysporum f.sp. opuntiarum as a monophyletic group, and supported the resolution of F. oxysporum f.sp. gladioli into two distinct major clades. The results indicate that F. oxysporum f.sp. dianthi and f.sp. gladioli have a paraphyletic origin. Pathogenic isolates associated wtih wilt and rot diseases have also been identified in F. redolens, a species closely related to F. oxysporum. Contrary to the commonly accepted view of conspecificity of both species involved, F. redolens can be differentiated from F. oxysporum in several ways including gene genealogies, isozyme polymorphisms, and AFLP fingerprints. In several cases, however, the disease symptoms caused by both fungi on a given host are indistinguishable. Within F. redolens, also an asexual fungus, clonal lineages have been identified in a similar manner as in F. oxysporum. Besides six VCGs in F. oxysporum f.sp. dianthi, wilt-inducing isolates belonging to four VCGs (corresponding to four unique races) have been identified in F. redolens f.sp. dianthi (Baayen et al., 1997). Next to F. oxysporum f.sp. asparagi, causal agent of asparagus root rot, similarly pathogenic isolates occur in F. redolens that should be classified as a distinct forma specialis, F. redolens f.sp. asparagi. Similarly, pathogenic isolates of F. redolens ff.spp. spinaciae and pisi exist next to F. oxysporum ff.spp. spinaciae and pisi proper. Gene genealogies indicate that three major clades exist within F. redolens, harboring VCGs belonging to distinct formae speciales in a similar complex pattern as for F. oxysporum. Horizontal gene transfer may be involved in the evolution of pathogenicity to the same host in distinct (lineages within) species.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Cees Waalwijk, Peter J. M. Bonants, Robert P. Baayen
Research topic(s) for pests/diseases/weeds:
identification/taxonomy
