Detection of avocado sunblotch viroid in chloroplasts of avocado leaves by in situ hybridization.

In situ hybridization experiments were carried out to detect avocado sunblotch viroid (ASBVd) in foliar tissue of avocado, using a digoxigenin-labelled RNA probe complementary to the ASBVd-RNA in sections of aldehyde-fixed, LRGold-embedded leaf samples. Detection of the probe was made through anti-digoxigenin antibody and protein-A colloidal gold (20 nm). Seventy to 80% of the signals came from chloroplast while the cytoplasm and vacuole were labelled with ca. 10% of the gold particles. This is in contrast with the subcellular localization of potato spindle tuber viroid and some other related viroids, which are mainly found in the nucleus.