Detection and tissue distribution of potato spindle tuber viroid in infected tomato plants by tissue print hybridization

Potato spindle tuber viroid (PSTVd) was detected in two cultivars of tomato (Lycopersicon esculentum Mill.) by tissue print hybridization of cross-sections of stem and rhachis, using a S-35-labeled PSTVd RNA probe. PSTVd was detectable in the viroid-sensitive and symptom-developping cv ''Rutgers'' 2 weeks p.i., and in the viroid-tolerant and practically symptomless cv ''Goldkugel'' 3 weeks p.i. In both tomato cultivars, PSTVd accumulated in the upper parts of the plants newly grown after inoculation. It was predominantly found in association with the ring formed by the vascular tissue. The final accumulation of PSTVd as well as its spatial distribution were similar in the sensitive and in the tolerant tomato cultivar, as estimated from the tissue print autoradiographs. Thus, tissue print hybridization provides a rapid and sensitive means for viroid diagnosis and for the assessment of tissue-specific localization of the viroid RNA.