USE OF CELLULOSE-ACETATE ELECTROPHORESIS FOR RAPID IDENTIFICATION OF ALLOZYME GENOTYPES OF PHYTOPHTHORA-INFESTANS

Cellulose-acetate electrophoresis (CAE) provided excellent resolution of allozyme genotypes of Phytophthora infestans at the two loci Glucose-6-phosphate isomerase (Gpi) and Peptidase (Pep). The cellulose-acetate system has many advantages over traditional starch gel analyses. It is much faster, running in only 15 to 20 min compared to 16 to 18 h for starch gels, and because of the short run times the gels do not need to be cooled during electrophoresis. Cellulose acetate is purchased as precast plates, which eliminates the time required to pour starch gels. Both Gpi and Pep can be analyzed using a single buffer in the CAE system, whereas four buffers are required to resolve these enzymes using starch gels. Finally, only very small amounts of tissue (e.g., 3,000 sporangia washed from lesions or infected tuber slices) are required for CAE, so it can be useful even when the fungus has not been isolated into axenic culture. These advantages may allow CAE to be useful as a diagnostic tool in field situations, where rapid determination of genotypes could aid disease management strategies. Because populations of P. infestans in the United States and Canada currently are highly clonal, mating type and response to metalaxyl are highly correlated with allozyme genotype. Therefore, CAE of allozyme genotypes could provide a rapid, accurate method for predicting mating types and metalaxyl sensitivities of P. infestans within fields.