VARIABILITY OF MITOCHONDRIAL-DNA AS AN INDICATOR OF RELATIONSHIPS BETWEEN POPULATIONS OF FUSARIUM-OXYSPORUM F-SP MELONIS

Mitochondrial DNA from a reference strain of Fusarium oxysporum f. sp. melonis was cloned and filter hybridized to total DNA of 78 strains. A distinct mtDNA restriction fragment pattern corresponded to each of six vegetative compatibility groups (VCGs); two additional VCGs shared the seventh pattern. Vegetatively self-incompatible strains were associated with a VCG by restriction pattern. Length and restriction site variations were catalogued for all restriction patterns providing a quantitative measure of genetic distance among VCGs. Six VCGs congregated into three close clusters. The two remaining VCGs were separated from these clusters by a greater distance. The distant VCGs included a strain representing an isolated population and an avirulent strain which is a possible outgroup. Different VCGs containing the same race were not necessarily closely related. It could not be concluded that F. oxysporum f. sp. melonis, a group unified by pathogenicity, is monophyletic. MtDNA can be used to identify isolated populations within F. oxysporum defined by VCG. © 1990, British Mycological Society. All rights reserved.