STUDIES ON THE DIAGNOSIS OF HOP STUNT VIROID IN FRUIT-TREES - IDENTIFICATION OF NEW HOSTS AND APPLICATION OF A NUCLEIC-ACID EXTRACTION PROCEDURE BASED ON NONORGANIC SOLVENTS

A non-radioactive digoxigenin-labelled RNA probe specific for hop stun t viroid (HSVd) diagnosis has been developed. The high sensitivity and specificity of this RNA probe in dot blot hybridizations to nucleic a cids from field samples, allowed the confirmation of the presence of H SVd in apricot (Prunus armeniaca L.) and its detection in two fruit tr ee species not previously described as hosts of this pathogen, almond (Prunus dulcis Miller) and pomegranate (Punica granatum L.). This resu lt supports and extends the notion of the world wide distribution of H SVd, infecting cultivated fruit trees. HSVd was also found to accumula te to much higher levels in mature apricot fruits than in leaves. Addi tionally, a sample processing procedure which does not involve the use of organic solvents was demonstrated to render faithful results when used for viroid detection. The combined reliability and facility of us e of both this extraction procedure and the non-radioactive probe will benefit agronomic investigations addressing the detection and eradica tion of HSVd. Other applications of the work described here, as the st udy of possible causal relations between specific disorders and HSVd i nfection, an also discussed.