Multiple infection with citrus viroids other than citrus exocortis viroid in Satsuma mandarin trees on trifoliate orange rootstock and its influence on the trees

Abstract

We investigated Satsuma mandarin 'Haraguchi Wase' trees on trifoliate orange rootstocks showing exocortis-like symptoms. The results of bioassay using 'Etrog' citron (Arizona) 861-S1 and RT-PCR showed that the trees were infected with 1 to 4 citrus viroids but not with citrus exocortis viroid (CEVd). According to a survey, the more serious was the damage to the rootstock, the larger was the decrease in tree canopy volume and trunk diameter. It appeared that multiple infection caused enormous damage, such as bark scaling, which is normally characteristic of CEVd infection in trifoliate orange rootstock. We suspect that hop stunt viroid (HSVd) and citrus viroid-III (CVd-III) in the viroid complex causes severe symptoms in trifoliate orange rootstock, and that additional infection with CVd-OS and/or CVd-I-LSS causes even worse damage.