MULTIPLE EVOLUTIONARY ORIGINS OF THE FUNGUS CAUSING PANAMA-DISEASE OFBANANA - CONCORDANT EVIDENCE FROM NUCLEAR AND MITOCHONDRIAL GENE GENEALOGIES

Panama disease of banana, caused by the fungus Fusarium oxysporum f. s p. cubense, is a serious constraint both to the commercial production of banana and cultivation for subsistence agriculture. Previous work h as indicated that F. oxysporum f. sp. cubense consists of several clon al lineages that may be genetically distant. In this study we tested w hether lineages of the Panama disease pathogen have a monophyletic ori gin by comparing DNA sequences of nuclear and mitochondrial genes. DNA sequences were obtained for translation elongation factor 1 alpha and the mitochondrial small subunit ribosomal RNA genes for F. oxysporum strains from banana, pathogenic strains from other hosts and putativel y nonpathogenic isolates of F. oxysporum. Cladograms for the two genes were highly concordant and a partition-homogeneity test indicated the two datasets could be combined. The tree inferred from the combined d ataset resolved five lineages corresponding to ''F. oxysporum f. sp. c ubense'' with a large dichotomy between two taxa represented by strain s most commonly isolated from bananas with Panama disease. The results also demonstrate that the latter two taxa have significantly differen t chromosome numbers. F. oxysporum isolates collected as nonpathogenic or pathogenic to other hosts that have very similar or identical elon gation factor 1 alpha and mitochondrial small subunit genotypes as ban ana pathogens were shown to cause little or no disease on banana. Take n together, these results indicate Panama disease of banana is caused by fungi with independent evolutionary origins.