INDUCTION OF SYSTEMIC RESISTANCE IN PEA TO PEA POWDERY MILDEW BY EXOGENOUS APPLICATION OF SALICYLIC-ACID

Exogenous application of salicylic acid (SA) solutions to pea leaves i nduced systemic resistance to Erysiphe pisi, reducing by 20-30% the pe rcentages of fungal germlings that successfully infected untreated lea ves of SA-treated plants. SA concentrations of 1.5 and 15 mM were simi larly effective, but 0.15 mM had no detectable effect. While 15 mM SA solutions were phytotoxic, 1.5 mM solutions caused no apparent damage indicating that resistance induction was not due to tissue damage. The induced resistance persisted for at least 13 days after treatment, bu t excision of treated leaves 1 day after SA application prevented full induction of systemic resistance, and the resistance was not expresse d if untreated leaves were inoculated fewer than 3 days after SA appli cation. The effect of SA was transmitted to leaves at nodes both above and below treated leaves. Chemical induction of systemic resistance m ay provide an additional means for controlling pea diseases.