MITOCHONDRIAL-DNA RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS IN FUSARIUM-OXYSPORUM F SP-NIVEUM

Mitochondrial DNA (mDNA) extracts from 13 isolates of Fusarium oxysporum f. sp. niveum, including 12 from widely separated geographic regions within the United States and representing the three races, and one race 2 isolate from Israel, were examined for the presence of plasmid DNA and were also subjected to restriction endonucleases analysis. None of the mtDNA from any isolate had a copurifying plasmid. The estimated size of mtDNA from f. o. f. sp. niveum race 0, calculated as the average of the sum of restriction fragment sizes, was 45.1 +/- 2.2 kb. The restriction enzymes BamHI, EcoRI, HpaI, HindIII and MboI resolved 2, 4, 9, 21, and more than 40 fragments, respectively, but no polymorphisms were observed among the 13 isolates with any of these endonucleases. However, PstI digestion showed three distinct polymorphic patterns among the isolates. Each appeared to derive from point mutations that resulted in a change of one or more restriction sites. The most common pattern was present in nine of the isolates (three of race 0, four of race 1, and two of race 2) and included a 1.5 kb fragment. A second polymorphic pattern occurred in three USA isolates (one each of race 0, race 1 and race 2) and was characterized by an apparent replacement of the 1.5 kb fragment by 0.6 and 0.9 kb fragments. The Israeli isolate [ISL-59(73) race 2] had a unique pattern lacking the 1.5 and 2.0 kb fragments present in the common pattern and, instead, had 0.6, 0.9 and 3.0 kb fragments. The mtDNA polymorphisms observed among the USA isolates were not correlated with either pathological race or geographic region of origin.