Pear blister canker viroid: Host range and improved bioassay with two new pear indicators, Fiend 37 and Fiend 110

An investigation was conducted to improve the biological detection of pear blister canker viroid (PBCVd), which over a period of 2 to 3 years induces pear blister canker disease on the perry pear (Pyrus communis) cv. A20. PBC Vd was not detected by dot blot hybridization or bioassay in any of the tes ted species of Amelanchier, Aronia, Cotoneaster, Crataegus, and Pyracantha. However, some species of Chaenomeles, Cydonia, and Sorbus, five out of 13 species of Malus, 15 Pyrus species, and 16 commercial pear cultivars were s usceptible to PBCVd, although none developed symptoms. Only in perry pear s eedlings did approximately 5% of the population react to infection with pur e PBCVd strains by developing petiole, leaf, or bark necrosis 2 to 3 years (cv. A20) or 3 to 5 months (cv. Fieudiere) after inoculation. The selected Fiend 37 and Fieud 110 clones are proposed as PBCVd indicators to replace A 20. Results from bioassays on the indicators and from detection by a PBCVd- cRNA probe were essentially in agreement except for some Malus species.