Abstract:
Biological indexing is based upon the ability of certain plants, referred to as indicator plants or indicators, to produce specific symptoms when inoculated with a pathogen using mechanical means or grafting. In the case of citrus viroids, clonal indicators are grafted on to vigorous rootstocks such as rough lemon (Citrus × granulata Raf.). The \'Arizona-861-S-1\' citron clonal indicator (C. medica L.) can detect and bioamplify all citrus viroids; however, for specific citrus variants of the hop stunt viroid (i.e., CVd-IIb and CVd-IIc), the clonal indicator \'Parson\'s special # 9\' mandarin (C. reticulata Blanco) is preferred. Inoculation techniques and symptom expression are described in detail. Other supporting elements, such as greenhouse conditions and propagation techniques, are also presented.