Altered cytokinin pattern and enhanced tolerance to potato virus Y-NTN in the susceptible potato cultivar (Solanum tuberosum cv Igor) grown in vitro

Plants of the susceptible potato cultivar Igor systemically infected with potato virus Y-NTN were grown in tissue culture. The symptoms of infection which are strongly expressed in soil-grown plants were suppressed and plantlets exhibited an enhanced tolerance to PVYNTN. Determination of nine endogenous cytokinins in virus free and infected plantlets revealed an increase in total cytokinin level in systemically infected potatoes. This elevation was due mainly to a seven-fold increase in levels of zeatin riboside and an 18-fold increase in the concentration of the biologically inactive iso-pentenyl adenine-g-glucoside. Although the amount of g-glucosilation of iso-pentenyl adenine was significant, total cytokinin deactivation did not exceed 23%. The possible role of the observed changes in cytokinin concentrations in the control of symptom development and resistance is discussed.