Effect of exogenous cytokinins on dynamics of development and differentiation of infectious structures of the pathogen of wheat powdery mildew

The infectious structures for the development and differentiation of Erysiphe graminis DC. f. sp. tritici March., the pathogen of wheat powdery mildew, under the effects of exogenous zeatin was studied by methods of light and electron scanning microscopy. It was shown for the first time that physiologically active substances, specifically phytohormones of the cytokinin type, can affect dimensions of the halo revealed in the pathogen penetration site at cytochemical staining. Treatment with zeatin affected conidia germination and pathogen growth in the ectophytic stage. The concentration curve of the action of zeatin for the number of mature pathogen colonies (6 days after infection) was represented by a multiphase curve with two maxima (1 and 3 μM) and one minimum (1.5 μM). Similar curves have been obtained for the number of normal appressoria and for large halo diameters, which possibly indicates the existence of the factors affecting these both parameters, as well as the final number of pathogen colonies. The obtained data indicate that the origin of the multiphase dose response curve for effect of cytokinins on the development of powdery mildew pathogen is connected with factors that are active at the early stages of pathogenesis.