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 milde w between susceptible and partially resistant cucumber cultivars were found when 2,6-dichloroisonicotinic acid (INA) was used as a model sub stance. In the partially resistant cv. Flamingo, EC(50) was approximat ely 0.25 mg/l. In the susceptible cvs Corona and Lange Groene Gigant i t was approximately 6 mg/l. In greenhouse experiments with cv. Flaming o, powdery mildew could be well controlled with fortnightly applicatio ns in doses as low as 0.5 mg/l. The effect was highly cumulative.