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Multiple Citrus Viroids in Citrus from Japan and Their Ability to Produce Exocortis-Like Symptoms in Citron

First and seventh authors: Department of Citrus Research, National Institute of Fruit Tree Science, Kuchinotsu, Nagasaki 859-2501, Japan; second author: Department of Grape and Persimmon Research, National Institute of Fruit Tree Science, Akitsu, Hiroshima 729-2494, Japan; third author: Faculty of Horticulture, Minami Kyushu University, Takanabe, Miyazaki 884-0003, Japan; fourth author: National Institute of Fruit Tree Science, Tsukuba, Ibaraki 305-8605, Japan; fifth author: Biotechnology Institute, Akita Prefectural University, Ohgata, Akita 010-0444, Japan; sixth author: Graduate School of Agriculture, Hokkaido University, Sapporo, Hokkaido 060-8589, Japan; eighth author: Yamato Post-entry Quarantine Center, Yokohama Plant Protection Station, Yamato, Kanagawa 242-0006, Japan; and ninth author: Headquaters, National Agricultural Research Organization, Tsukuba, Ibaraki 305-8517, Japan

Sequential polyacrylamide gel electrophoresis analyses showed many viroid-like RNAs in samples collected from citrus trees in Japan. Reverse transcription polymerase chain reaction and sequencing analyses of the amplified fragments verified that they were derived from variants of six citrus viroids, Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd) including CVd-I-LSS (a distinct variant of CBLVd), Hop stunt viroid, Citrus viroid III, Citrus viroid IV, and Citrus viroid OS. The samples induced symptoms with variable severity in Arizona 861-S1 ‘Etrog’ citrons (Citrus medica L.) likely due to the varying accumulation patterns produced by the different viroids. Some of the symptoms caused by the samples harboring the citrus viroids other than CEVd were as severe as those caused by CEVd. Some source citrus trees showing the severe bark scaling characteristic of exocortis disease in trifoliate orange (Poncirus trifoliata (L.) Raf.) rootstocks contained only citrus viroids other than CEVd in complex. This indicates that certain exocortis-like diseases in Japan were caused by some combination of citrus viroids not including CEVd.

Additional keywords: cachexia, nucleotide sequence, variation.