Integrated control of potato late blight with a combination of the photosynthetic bacterium Rhodopseudomonas palustris strain GJ-22 and fungicides

Late blight caused by the oomycete Phytophthora infestans is the major yield-threatening disease in potato production. An isolate of the photosynthetic bacterium Rhodopseudomonas palustris, GJ-22, was previously evaluated for its ability to promote the growth and enhance the immune response of solanaceous plants. In the present study, GJ-22 was shown to significantly repress disease symptom development caused by P. infestans in potato tubers. Curzate (cymoxanil plus mancozeb), a widely used fungicide with high activity against P. infestans, was selected for use in combination with GJ-22. The sensitivity of GJ-22 to the fungicides cymoxanil and mancozeb was tested. The growth of GJ-22 was unaffected by up to 100 mg l(-1) cymoxanil or 50 mg l(-1) mancozeb in photosynthetic medium. In greenhouse and field experiments, the combined application of GJ-22 and curzate resulted in better disease control than the use of either agent alone. In addition, treatment with 1 x 10(7) CFU ml(-1) GJ-22 plus 700 mg l(-1) curzate showed synergistic effects in the field trial. Our results highlight the potential to control potato late blight with the combination of R. palustris strain GJ-22 and curzate, providing environmentally friendly protection with a reduced level of fungicide application.