Phytogard® (K2HPO3) induces localized resistance in cauliflower to downy mildew of crucifers

Phytogard(R), a formulation containing 58% potassium phosphonate (K2HPO3) and 42% water was tested for its ability to protect cauliflower (Brassica oleracea var. botrytis) from downy mildew of crucifers (Peronospora parasitical. A dose-response analysis was conducted and concentrations of 0.0, 0.5, 5.0, 6.0, 7.0 and 10.0 ml/l of water were tested on seven-day old seedlings using the spray method. On 30-day old plants, concentrations of 7.0, 10.0 and 20.0 ml/l were tested using the same spray method. Results showed that when applied before or after inoculation, Phytogard(R) provided complete protection (no sporulation) of seedlings with concentrations of 7.0 ml/l or higher. On young plants, complete protection was obtained at 10 ml/l. It was also shown that the induced resistance was not systemic but lasted at least 15 days after treatment. However, when Phytogard was applied on roots of 30-day old plants, all leaf stages were completely protected probably due to the ascendant transport of the compound. In another experiment, it was shown that Phytogard(R) at 7 ml/l inhibits germination of 53% of the spores. SDS-PAGE gels colored with silver nitrate revealed that the protein profile of treated plants was not modified by treatment with the compound. However, when the protein extracts were concentrated (10 x), results obtained showed that beta-1,3 glucanase activity and PR2 proteins were weakly induced. These results suggest that resistance induced by Phytogard(R) is probably strongly localized. (C) 2000 Elsevier Science Ltd. All rights reserved.