The Phytotoxin Thaxtomin A Is the Primary Virulence Determinant for Scab Disease of Beet, Carrot, and Radish Caused by .

Several species of cause common scab, a major disease of potato, primarily through the phytotoxic effects of the phytotoxin thaxtomin A. Several phytopathogenic species have also been implicated as the causative agents of scab diseases of taproot crops including beet, carrot, radish, parsnip, and turnip. But the molecular mechanisms employed by to infect these crops is unknown. In this work, we tested the hypothesis that thaxtomin A biosynthesis is also necessary for -caused scab of beet, carrot, radish, and turnip. Thaxtomin A induced plant stunting and cell death of all four of these species. mutants in which the transcriptional regulator of thaxtomin A biosynthesis is disrupted were nonvirulent on all four crops, and complementation of the transcriptional regulator rescued thaxtomin A biosynthesis and plant pathogenicity to wild-type levels. These results demonstrate that thaxtomin A is the primary virulence determinant of scab disease of these other crops.