Survey of coconut cadang-cadang, viroid sequence in oil palm with orange spotting disorders using molecular diagnostic tools
2009
Vadamalai, G. | Cheng, L.C. | Othfurihan, O. | Tan, Y.H.
The lethal cadang-cadang disease of coconut palms (Cocos nucifera L.) in the Philippines is caused by coconut cadang-cadang viroid (Pospiviroidae:Cocadviroid). It has caused extensive losses to coconut production in the Philippines. Several species of palm and other monocotyledons in Oceania and South-East Asia have been shown by molecular hybridization assay to contain CCLVd-related sequences. In African oil Palm (Elaies guineensis) plantations in South East Asia and the South Pacific, CCCVd-related molecules were frequently associated with an orange leaf spotting disorder previously described as 'genetic' orange spotting (GOS). In this study, variants of CCCVd have been identified in plantation oil palms with orange spotting disorder growing in Malaysia. These variants were detected by molecular hybridization of dot blots and Northern blots of two-dimensional polyacrylamide gels (2D-PAGE)with a sup32P-labeled 246 nt form of CCCVd (CCCVd sub 246) cRNA probe. In addition, a ribonuclease protection assay (RPA) has been developed for detecting the 246 nt sequence of CCCVd. It has been widely used as a powerful sensitive method to detect and quantify specific RNAs and its variations in nucleotide sequence of a RNA population. A small scale survey in three commercial plantations in Malaysia showed OS incidence ranging from 13-16%. Thirty palms were screened for CCCVd sequences using methods described above and 17 out of 30 commercial oil palms sampled contained CCCVd sequences. Cloning and sequencing of RT-PCR products from the oil palm showed over 90% sequence similarity to the 296 nt form of CCCVd (CCCVd sub 246) from the Philippines. Three size classes are described comprising 297, 293 and 270 nt. Mutations and deletions accounted for the different sizes. At present, OS is not considered to be economically important, hence, no major research effort has been carried out to investigate this problem, especially the etiology and epidemiology of the disorder. However, with this evidence, serious consideration is needed to study the threat of CCCVd to the oil palm industry.
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