DIFFERENTIAL INDUCTION OF RESISTANCE AND ENHANCED ENZYME-ACTIVITIES IN CUCUMBER AND TOBACCO CAUSED BY TREATMENT WITH VARIOUS ABIOTIC AND BIOTIC INDUCERS

Systemic-induced resistance was established in tobacco and cucumber plants by treatment with various inducers. Extracts from Reynoutria sachalinensis, silica preparations (Hornkiesel P 501), or aspirin, when applied 1-3 days before the challenge inoculation, more effectively inhibited disease development than inducers from bacterial or fungal cultures. The inducers did not reduce disease development by directly inhibiting the growth of pathogens. Treatment with inducers led to an increase in activities of chitinase, beta-1,3-glucanase, peroxidase, polyphenol oxidase, phenylalanine ammonia lyase in cucumber and tobacco leaf tissue and additionally in tobacco to an increase in lysozyme activity. However, the extent and the time-course of the increase varied according to the inducer and host plant. The increase in resistance and the activity of particular enzymes were not closely correlated. The time-course of resistance and increased enzyme activities in cumcumber was also correlated with increased formation of papillae in epidermal cells.