Coconut cadang-cadang viroid and coconut cadang-cadang viroid-like organisms in the Pacific region
Coconut cadang-cadang viroid (potential EPPO A1 quarantine pest) (CCCVd) was first detected in the Philippines. A survey sponsored by the Australian Center for International Agricultural Research (ACIAR) was carried out to determine the occurrence of the disease in the South Pacific region. As reported at the 6th International Congress of Plant Pathology in Montreal, 2500 samples have been collected within the region including species of coconut, oil and other palms, Pandanaceae and herbaceous monocotyledons such as Zingiberaceae, Marantaceae and Commelinaceae. The samples were investigated for the presence of CCCVd by eloctroblot hybridization using a full length cRNA probe homologous to CCCVd.
A range of small nucleic acids with secondary molecular structure and nucleotide sequences similar to CCCVd have been detected in a high percentage of members of numerous species from all locations surveyed. The oil palms with CCCVd-related molecules showed severe orange spotting and stunting, symptoms resembling those of CCCVd infection in the Philippines and that of "genetic" orange spotting (GOS). The authors believe that the GOS is caused by viroid allied to CCCVD and which is infectious to coconut. Coconut palms containing CCCVD-related sequences outside the central Philippines do not show the typical cadang-cadang syndrome, but sometimes seem stunted, low-bearing or chlorotic. The authors consider that these isolates represent variants of the CCCVd. CCCVd-like sequences with a strong homology to CCCVd were also found in herbaceous monocotyledons infecting over 60% of the species sampled, but appearing generally symptomless. Malaysia and Sri Lanka had the highest rank of viroid infection. Pathogenicity tests for these isolates, however, have not been carried out yet. The authors concluded that viroids related by nucleotide sequence homology to CCCVd occur widely in palms and other monocotyledons outside the Philippines.
Sources
Hanold, D.; Randles, J.W. (1993) A new viroid family infecting tropical monocotyledons.
Presentation at the 6th International Congress of Plant Pathology, Montreal, CA, 1993-07/08-27/06.