Influence of cytokinines on in vitro growth and pigmentation of healthy and citrus exocortis viroid-infected Gynura aurantiaca (Blume) DC

Citrus exocortis viroid (CEVd) is an economically important plant pathogen which infects a broad range of hosts. In order to investigate complex interactions among viroid, host growing conditions and plant secondary metabolism that constitute the viroid pathogenesis pathway, we set up an in vitro system for the cultivation of CEVd-infected and viroid-free Gynura aurantiaca (Blume) DC. shoots. Both, basal Murashige and Skoog (MS) medium and MS medium supplemented with cytokinines supported the growth of CEVd-infected and healthy shoots, but viroid-free shoots performed better than infected ones. The addition of cytokinines to the media induced an increase in the concentration of purple-reddish pigment, cyanidin tetra-glucoside (GAA), which did not depend on the presence of viroid. The clear differences in single strand conformation polymorphism (SSCP) patterns between CEVd isolates obtained from plants grown on medium supplemented with cytokinines and those obtained from plants grown on basal MS medium or in the greenhouse, indicate that cytokinines may influence not only plant metabolism, but also viroid population structure.