Continuous exposure to light results in reduced susceptibility to virulent Hyaloperonospora parasitica. HpNoco2 growth has been evaluated on plants pretreated for 3 days by normal light (dark grey) or continuous light (light grey) exposure. Two weeks old plants were sprayed with HpNoco2 (2*104 spores/ml) and spores were counted 7 dpi. Bars represent mean value of spores/seedling from four different experiments. Based on T-tests differences between normal light and constant light treated samples were significant only for nahG plants (p = 0.0084).