Panama disease of banana, caused by the fungus Fusarium oxysporum f. sp. 
cubense, is a serious constraint both to the commercial production of banana and 
cultivation for subsistence agriculture. Previous work has indicated that F. 
oxysporum f. sp. cubense consists of several clonal lineages that may be 
genetically distant. In this study we tested whether lineages of the Panama 
disease pathogen have a monophyletic origin by comparing DNA sequences of 
nuclear and mitochondrial genes. DNA sequences were obtained for translation 
elongation factor 1alpha and the mitochondrial small subunit ribosomal RNA genes 
for F. oxysporum strains from banana, pathogenic strains from other hosts and 
putatively 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 dataset resolved 
five lineages corresponding to "F. oxysporum f. sp. cubense" with a large 
dichotomy between two taxa represented by strains most commonly isolated from 
bananas with Panama disease. The results also demonstrate that the latter two 
taxa have significantly different chromosome numbers. F. oxysporum isolates 
collected as nonpathogenic or pathogenic to other hosts that have very similar 
or identical elongation factor 1alpha and mitochondrial small subunit genotypes 
as banana pathogens were shown to cause little or no disease on banana. Taken 
together, these results indicate Panama disease of banana is caused by fungi 
with independent evolutionary origins.