Two linear plasmid-like DNAs designated pFSC1 (9.2 kbp) and pFSC2 (8.3 kbp) were found in an isolate of the plant pathogenic fungus Fusarium solani f. sp. cucurbitae race 1. The plasmids were maternally inherited and copurified with mitochondrial DNA obtained from a mitochondria-enriched cell fraction suggesting that they are located in mitochondria. The plasmids did not share extensive sequence similarity. No homology was detected between either plasmid and the nuclear or mitochondrial genome when cloned plasmids were used as probes in Southern hybridization analyses. The fungus was cured of plasmids by ethidium bromide treatment. Compared to the plasmid-containing isolate, plasmid-cured derivatives had reduced pathogenicity on a susceptible plant host, Cucurbita maxima "Pink Banana.".
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We express our gratitude to individuals who contributed Fusarium stocks for this study, Bob Metzenberg for generously providing the clone pMF2, and Don Cummings for the clone Pst-3. We also thank Ross Inman, Maria Schnoes, and Bill Russin for help with electron microscopy and Steve Vicen for assistance in preparing the iigures. This work was supported by USDA Grant 83-CRCR-I-135D, the USDA, and the Graduate School of the University of Wisconsin.