Effect of some immunomodulators and zeatin on susceptibility of wheat to powdery mildew.

The effects of zeatin, salicylic acid, and plant oligoadenylates on susceptibility of wheat seedlings to powdery mildew and the shape of dose-response curves for immunomodulation were studied. Salicylic acid and zeatin produced complex dose-responses with upregulation or downregulation of plant susceptibility. Under different experimental conditions, the dose-response curve for zeatin varied in shape from a curve with a maximum to a curve with a minimum of susceptibility to powdery mildew. More complicated curves with a resistance region framed with regions of increased susceptibility were also found. Plant oligoadenylates inhibited the development of powdery mildew at optimal concentrations. The increasing concentrations of salicylic acid and plant oligoadenylates, when combined with zeatin, led to a gradual change in the shape of the zeatin concentration curve. Treatment with salicylic acid and plant oligoadenylates in these experiments may simulate plant responses under biotic and abiotic stresses. Thus, exogenous zeatin was applied to model changes in the phytohormone metabolism. The complex multiphase nature of dose-response is proposed to cause a kind of random-number generator that produces variability in the physiological and immunological status of plants in natural conditions. Variation in susceptibility of individual plants may be crucial for the survival of infected plants and the stabilization of plant-pathogen interactions. [ABSTRACT FROM AUTHOR]