Coconut Cadang-Cadang Disease and Its Viroid Agent
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D. Hanold and J. W. Randles Waite Agricultural Research Institute, University of Adelaide Glen Osmond, South Australia Coconut Cadang-Cadang Disease and Its Viroid Agent In the early 1930s a devastating epi- cadang-cadang must be considered a occurs rarely in the field but has been demic of a lethal disease of coconut palm serious economic threat (21). observed in about 3% of mechanically (Cocos nucijera L.) was reported from Tinangaja disease is still prevalent on inoculated coconut palms at the Albay southern Luzon in the Philippines. It was Guam. Its economic importance is less Research Center in the Philippines. Parts appropriately named "cadang-cadang" evident, however, because coconuts are of the fronds consist only of the midribs, disease from the word gadan-gadan of not commercially produced there at thus showing a "brooming" syndrome the local dialect meaning "dying" (13). present (2). (Fig. 2). Anecdotal reports indicate that the dis- Tinangaja disease shows symptoms ease probably occurred a few years Symptoms and Host Range similar to those of cadang-cadang except earlier in the Philippines, at about the Cadang-cadang develops slowly in that the affected trees bear spindle- time a somewhat similar epidemic was palms and cannot be unequivocally iden- shaped nuts with a reduced or absent reported on the island of Guam. The tified on the basis of symptoms at a single kernel (2) (Fig. 3). There are a number disease in Guam was called "tinangaja" observation. The disease progresses through of diseases of coconut palm with un- and was extremely destructive to the three well-defined stages (13) (Fig. 1). In known etiology, some of which show island's coconut population (2). Both the early stage, nuts become rounded, abnormalities reminiscent of cadang- diseases have now been shown to be with characteristic equatorial scarifica- cadang or tinangaja, for example, narrow caused by related viroids: coconut tions, and the first nonnecrotic, trans- nuts as for Tatipaka disease and a decline cadang-cadang viroid (CCCVd) and lucent, bright yellow leaf spots appear. as for Kerala wilt, both diseases occur- coconut tinangaja viroid (CTiVd). In the mid stage, inflorescences become ring in India. Some of them have tested necrotic, nut production ceases, new negative by gel electrophoresis (3) and Economic Importance frond production slows down, and leaf solution molecular hybridization assay It has been estimated that over 30 spots become larger and more frequent (12), but they need to be reevaluated by million coconut palms have been killed so that fronds begin to appear chlorotic the latest molecular diagnostic methods by cadang-cadang since it was first recog- from a distance. In the late stage, pre- for the presence of viroid. nized (22). Based on average yield and ceding death, leaf spots are almost Oil palm (Elaeis guineensis Jacq.) copra prices, the loss of production has confluent; the whole crown is distinctly naturally infected or inoculated with been valued at about $80-$100 (U.S.) for yellowish or bronze-colored and very CCCVd in the Philippines develops each planting site occupied by an infected much reduced in size and number of bright orange leaf spots that are larger tree (l3), an amount exceeding 2 months' fronds. The early stage lasts 2-4 years, and more numerous on the older fronds salary for an unskilled worker in the Phil- the mid stage approximately 2 years, and (Fig. 4), nut production ceases, and the ippines. According to G. Persley (in a the late stage about 5 years. The overall tree eventually dies (14). Naturally in- paper presented in 1989 to the Technical time from first symptoms to death of the fected buri palm (Corypha elata Roxb.) Advisory Committee of the Consultative tree is about 8 years for 22-year-old shows chlorotic leaf spots and stunting Group on International Agricultural palms and about 16 years for 44-year- (14). Palm species successfully inoculated Research), at least 96% of the total world old palms (22). Usually, palms become with CCCVd include oil palm, buri palm, copra production is provided by small- naturally infected only after they have betelnut palm (Areca catechu L.), golden holders. Because coconut is both an reached the age of flowering. In the rare cane palm (Chrysalidocarpus lutescens important subsistence and a major cash cases where younger palms become H. Wendl.), date palm (Phoenix crop in many developing countries, infected, they are stunted and fail to dactylifera L.), royal palm (Roystonea produce inflorescences, although they regia (Kunth) Cook), and Manila palm survive well past the age of first flower- (Veitchia rnerrillii (Becc.) Moore) (6,13). ing. Many cultivars and hybrids have Preliminary evidence suggests that Dr. Randles's address is: Department of Crop been tested for susceptibility by inocu- several herbaceous monocotyledonous Protection, Waite Agricultural Research Institute, lation in the Philippines, but none have species growing near coconut palms University of Adelaide, Glen Osmond, South Australia 5064. shown any indication of immunity to the infected with cadang-cadang (Fig. 5) viroid. The only known variation in the occasionally contain viroidlike molecules symptoms of cadang-cadang is a more with sequence similarity to CCCVd (J. @ 1991 The American Phytopathological Society severe type of lamina reduction that M. B. Rodriguez, D. Hanold, and J. W. 330 Plant Disease/Vol. 75 No. 4 .