Sensitive and specific digoxigenin-labelled RNA probes for routine detection of Citrus tristeza virus by dot-blot hybridization

A non-radioactive dot-blot hybridization assay for the successful detection of Citrus tristeza virus (CTV) RNA in total nucleic acid extracts of infected citrus was developed. Two digoxigenin (DIG)-labelled minus-sense riboprobes, complementary to the coat protein gene sequence of a Chinese and an Apulian CTV isolate were synthesized. Several citrus tissues were evaluated as optimal virus source and leaf petioles were found appropriate material for reliable detection. The hybridization assay showed a detection limit corresponding to 0.2 mg of fresh infected tissue. The riboprobes allowed CTV detection in isolates from different geographical areas, grown in the screenhouse or in the field, resulting in similar hybridization patterns. The infected trees were tested during different seasons with positive results, although from July to August most of the samples gave a weaker hybridization signal, compared to other seasons. The high sensitivity and reliability of the molecular hybridization assay described make it a good alternative to serological methods for CTV detection.