Infection of Hordeum vulgare L. by Pyrenophora teres and of Zea mays by Dreschslera maydis were characterized by 'green island' formation, higher
cytokinin levels and accumulation of metabolites in the infected areas. Higher
cytokinin concentrations of the order 6-Y,Y-dimethylallylaminopurine > zeatinriboside >
zeatin > dihydrozeatinriboside were detected at
infection sites of susceptible hosts. By virtue of these
cytokinins,
infection sites may be acting as metabolic sinks helping proliferation of the pathogen. Existence of translocatory sinks at
infection zones was confirmed from autoradiographic studies, where, accumulation of labeled metabolites was prominent at
infection sites of susceptible hosts. Upon
infection the lower
cytokinin levels of resistant hosts decreased further with progress of
infection. In the infected resistant hosts the concentrations of
zeatin/zeatinriboside were the maximum among the four identified
cytokinins. The pathogen is also capable of secreting
cytokinins as evident from quantification of
cytokinins in culture filtrate extracts using HPLC. Since detached leaves were used in the experiments the increase/decrease of various
cytokinin levels may be attributed to pathogen influence. The increase in
cytokinin levels in the susceptible host may be aiding the growth of the pathogen on one hand, while the decrease in the infected resistant host may signal the host to activate defenses against a potential pathogen at the early stage of
infection.