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/1. In the susceptible cvs Corona and Lange Groene Gigant it was approximately 6mg/1. In greenhouse experiments with cv. Flamingo, powdery mildew could be well controlled with fortnightly applications in doses as low as 0·5 mg/1. The effect was highly cumulative.