Pear blister canker viroid.
Pear blister canker disease, first reported in France in the 1960's, is caused by pear blister canker viroid (PBCVd). Diseases can occur in several cultivars of pear (Pyrus communis), its major host, but most pear cultivars are tolerant and do not produce symptoms of infection. PBCVd was initially reported in pear and quince, followed by wild pear and nashi and can experimentally infect species in other genera (Chaenomeles, Cydonia, Sorbus, Malus). Transmission through mechanical inoculation from pruning tools and grafting to infective propagative materials is a potential pathway for spread; no animal vector is known and it is not known to be seed transmitted. PBCVd has been reported in several European countries, Malta, Tunisia, Turkey, Australia, Japan, China, and the Americas; the geographic distribution may be underestimated because of symptomless infections in certain hosts. PBCVd was placed on the A1 list in Canada in 1995, listed as a quarantine pest in the United States in 1989, is regarded as quarantine pathogen for Australia, and is listed in a certification scheme to produce clean Pyrus and Cydonia sp. planting material in an OEPP/EPPO Bulletin in 1999 (OEPP/EPPO, 1999).