EFFECTS OF CUCUMBER GENOTYPE ON THE INDUCTION OF RESISTANCE TO POWDERY MILDEW, SPHAEROTHECA-FULIGINEA, BY 2,6-DICHLOROISONICOTINIC ACID

Conspicuous differences in inducibility of resistance to powdery mildew between susceptible and partially resistant cucumber cultivars were found when 2,6-dichloroisonicotinic acid (INA) was used as a model substance. In the partially resistant cv. Flamingo, EC(50) was approximately 0.25 mg/l. In the susceptible cvs Corona and Lange Groene Gigant it was approximately 6 mg/l. In greenhouse experiments with cv. Flamingo, powdery mildew could be well controlled with fortnightly applications in doses as low as 0.5 mg/l. The effect was highly cumulative.