Apscaviroids Infecting Citrus Trees

Of the seven known citrus viroids, four are apscaviroids: citrus bent leaf viroid (CBLVd), citrus dwarfing viroid (CDVd), citrus viroid V (CVd-V), and citrus viroid VI (CVd-VI). Two (CDVd and CVd-V) are restricted to citrus, while CBLVd naturally infects hop and is also experimentally transmitted to avocado, and CVd-VI is present in natural infections of persimmon. The economic impact of these viroids on citrus is not only due to the direct damage caused by their specific diseases, but also to the synergistic effect of coinfection with other viroids. CDVd differs from the other citrus apscaviroids in that it causes reduction in size in susceptible hosts without any detrimental effects. It is used to obtain dwarfed trees for high-density plantings in several countries. CBLVd, CDVd, and CVd-V are reported in almost all citrus-growing countries, while CVd-VI has only been reported in Japan.