Abstract: Methods for the isolation and purification of the phytotoxin cercosporin are disclosed as well as methods for identifying microorganisms capable of degrading cercosporin. Cercosporin can be purified from members of the fungal genus Cercospora and incorporated into culture medium for selection of those organisms resistant to cercosporin. Once identified, these organisms can be used to isolate the protein and the gene responsible for conferring cercosporin-resistance. The gene can be cloned and inserted into a suitable expression vector so that the protein can be further characterized. Additionally, the DNA encoding for cercosporin-resistance can be inserted into a vector suitable for transforming an Agrobacterium and the Agrobacterium in turn used to transform plant cells normally susceptible to Cercospora infection. Plants can be regenerated from the transformed plant cells. In this way, a transgenic plant can be produced with the capability of degrading cercosporin.