First reported occurrence of citrus bent leaf viroid and citrus dwarfing viroid on imported oranges from China and lime fruits from Cambodia

Abstract

A number of viroids can cause serious damage on Citrus spp. ranging from stunting, bark scaling, yellowing and epinasty of leaves over stem pitting and gumming. However, so far, they have never been found in Thailand. In recent years, the import of orange and lime fruits from China and Cambodia, respectively, increased, and holds a substantial risk of viroid introduction and spread in Thailand. Orange and lime fruit samples in 2013 and 2014 were screened for the presence of citrus exocortis viroid (CEVd), hop stunt viroid (HSVd), citrus bent leaf viroid (CBLVd) and citrus dwarfing viroid (CDVd; CVd-IIId) by means of specific RT-PCR methods. Only CBLVd and CDVd were detected, clearly generating the expected amplification bands of around 320 and 300 base pairs, respectively. The presence of CBLVd and CDVd was confirmed by amplicon sequencing and RNA secondary structure analysis. About 34.2 and 19.5% of 41 samples (around 2300 fruits) of the imported lime fruit were infected with CBLVd and CDVd, respectively. CBLVd was detected in 62.3% of the 77 samples (around 2000 fruits) from imported oranges, while CDVd was found in 75.3%. This result indicates that the incidence of both CBLVd and CDVd in the imported citrus fruits is quite high. In addition, both viroid diseases have not been reported in Thailand. However, lack of information on the actual status of both viroids leads to difficulties in determining their impact on the Thai citrus industry.