COCONUT CADANG-CADANG VIROID

PENYAKIT 'CADANG-CADANG' pada tanaman kelapa (Cocos nucifera) merupakan satu ancaman. Penyakit ini dilaporkan berlaku di negara Filipina dan  pernah menjadi pandemik di negara tersebut. Ini menyebabkan segala bahan dan hasil kelapa dari Filipina DILARANG dibawah Akta Kuarantin Malaysia untuk dibawa masuk ke dalam negara. Patogen yang menyebabkan serangan penyakit ini adalah dikenali sebagai Viroid Cadang-cadang Kelapa (sejenis virus). Penulis blog yang pernah membuat tinjauan ke Filipina dan berjumpa dengan beberapa pegawai pakar tanaman kelapa dari Phiipines Coconut Authority (PCA) dahulu sering bertukat maklumat mengenai viroid ini. Berikut adalah tulisan yang saya sempat rujuk dari PCA untuk dijadikan bahan rujukan semua pembaca blog ini di Malaysia. After nearly seven decades of research on the once dreaded Coconut Cadang-cadang disease, caused by the Coconut Cadang-cadang Viroid (CCCVd) in which affects coconut palms in the Philippines, efforts made by the Philippine Government, through the Philippine Coconut Authority, have shown that the disease can be contained and managed. Some of the strategies discussed in the paper include: a) search for vector/s and their control, their host range, as well as for tolerant varieties; b) field transmission mechanism; c) establishment of disease boundaries and buffer zones along with continuous monitoring of the disease; d) issuance of policies and quarantine regulations/laws to be set up, and strict implementation of air, land and seaport checkpoints; e) early detection and assay of mother palms as disease-free sources of nuts for planting and replanting programmes; f) felling and burning of infected palms; g) continuous development and standardisation of highly-sensitive diagnostic protocols; and h) public awareness through information dissemination and campaigns. It is envisioned that with continuous implementation of these strategies, the import ban on coconut and its by-products imposed by some countries can be finally lifted following the declaration by the Australian Department of Agriculture and Water Resources of the lifting of its importation ban on fresh coconuts on 11 December, 2017. This scientific report of an article in "Anim Agriculture Technology" that I would like to share the information about Coconut Cadang-cadang Disease that able to damage coconut industry.

Coconut Cadang-cadang Disease (CCCVd) caused by coconut cadang-cadang viroids that grouped under viroids with family  known of  Pospiviroidae. Cadang-cadang is a disease caused by Coconut cadang-cadang viroid (CCCVd), a lethal viroid of Coconut (Cocos nucifera), Anahaw (Saribus rotundifolius), Buri Palm (Corypha utan), and Oil Palm (Elaeis guineensis). The name cadang-cadang comes from the word 'gadang-gadang' that means 'dying' in Philipines local dialect (Bicol). It was originally reported on San Miguel Island in the Philippines in year 1927/1928. And by 1962, all but 100 of 250,000 palms on this island had died from the disease," indicating an epidemic to Philipines. First time I as a bloggers come accross about cadang-cadang disease when I attended a technical management coconut training in UPLB, Los Banos, Manila about 20 years ago. Every year one million coconut palms are killed by CCCVd and over 30 million coconut palms have been killed since Cadang-cadang has been discovered. CCCVd directly affects the production of copra, a raw material for coconut oil and animal feed. Total losses of about 30 million palms and annual yield losses of about 22,000 tons of copra have been attributed to Cadang-cadang disease in the Philippines. Philipines are the second largest coconut growers in the world after Indonesia. During APCC Meeting 2018 held in Royl Chuln Hotel ,Kuala Lumpur by October 2018, I do chair the meeting that coconut experts from Philippines did mention the cadang-cadang disease as one threats to their coconut industry.

According to the experts, viroids are small, single-stranded RNA molecules, ranging from 246 to 375 nucleotides long. Unlike viruses, they do not code for protein coats but contain genes for autonomous replication. With abilities to cause serious disease, they are more commonly found in a latent stage, and their mode of infection is mainly mechanical, though documented cases exist of vertical transmission through pollen and seed. The sequence and structure prediction of CCCVd has been documented. There are four low-molecular-weight RNA species (ccRNAs) found associated with cadang-cadang disease. Of the four it believed that two are related with the early stage of the disease: ccRNA 1 fast and ccRNA 2 fast. After several years, two other species appear and predominate: ccRNA 1 slow and ccRNA 2 slow. Moreover, they share sequence homology with other viroids. Conditions for a viroid to infect its host include wounds on the host or infected pollen grain deposited into an ovule. Not all of the mentioned conditions pertain to cadang-cadang. Tinangaja disease is caused by coconut trinangaja viroid (CTiVd), which has 64% sequence homology with CCCVd. This disease has been found in Guam. Coconuts from Asia and South Pacific have been found to have viroids with similar nucleic acid sequences of CCCVd. The pathogenicity of CTiVd is uncertain. Coconut cadang-cadang viroid, also known as CCCVd, is responsible for a lethal disease of coconut plant first reported in the early 1930 in the Philippines. CCCVd is the smallest known pathogen and it is biologically distinct from other viroids; it consists of circular or lineal single-stranded RNA with a basic size of 246 or 247, it is thought it can be transmitted by seed or pollen (with low transmission rates) and occur in almost all plant parts. Once infected, coconut palm shows yellow leaf spots and nut production ceases; from appearance of first symptoms to tree death, time ranges from around 8 to 16 years, but the pest is generally greater in older plants. It is estimated that over 30 million coconut palms have been killed by cadang-cadang since it was first recognised and the loss of production is valued at about RM320 - RM400 for each planting site occupied by an infected tree.

The CCCVd is widely spread in Philippines and it is mostly found in Bicol Region, Masbate, Catanduanes, Samar and other smaller islands in the zone. It is known that the present northernmost boundary is at the latitude of Manila and the southernmost at the latitude of Homonhon Island. This fact is important due to the proximity of the disease to the major coconut and oil palm growing area of Mindanao.An isolated focus of infection has been found on Solomon Islands, Oceania. The available data at the present suggests that the epidemiology of cadang-cadang viroid may not be spreading into any specific route. In Guam, a similar viroid known as Coconut Tinangaja Viroid (CTiVd) has been found that causes a similar disease named tinangaja disease. This viroid has 64% sequence homology with the cadang-cadang viroid. There are other related viroids with the CCCVd, which are found in Asia and the South Pacific. They have a high degree of homology but the pathogenicity is uncertain. The mode of natural inoculation of the viroid is unknown. There has been evidence that the transmission through pollen and seed can occur but they have a very low transmission rates: progenies of healthy palms pollinated with diseased pollen, exhibited disease symptoms 6 years after germination.  CCCVd can spread through mechanical inoculation primarily through contaminated farm tools such as harvesting scythes or machetes, due to the improper sanitary conditions. The efficiency of the mechanical inoculation has been influenced by factors such as the age of the test plant and the mode of inoculation. The natural hosts of cadang-cadang identified are Cocos nucifera, Corypha utan, Elaeis guineensis and also Roystonea regia. The experimental hosts are Adonidia merrillii, Areca catechu, Caryota cumingii, Dypsis lutescens, Saribus rotundifolius, Phoenix dactylifera, Ptychosperma macarthurii and Roystonea regia.

The diagnosis by symptoms is not reliable enough so it’s better to do a molecular diagnosis based in test samples. Some of these methods (like Dot-blot hybridisation) allow the scientists to detect the viroid even six months before noticing the first symptoms. The first step is the purification to obtain the nucleic acids of the plant cells. The leaves of the plant located four or more below the spare leaf are cut. They are blended (homogenize) with sodium sulfite. Then the extract is filtered and clarified by centrifugation  10.000 g during 10 minutes). The next step is to add polyethylene glycol (PEG). Finally, after nearly two hours of incubation at 4 °C, and after another centrifugation (at low speed) the nucleic acids can be extracted by using such as chloroformprocedures. When approximately 1 gram of coconut tissue has been purified, the electrophoresis method can be started, which will help to identify the viroid by its relative mobility. The CCCVd is analysed in one or two dimensional polyacrylamide gels with a silver stain. The viroid can also be detected by a more sensitive method called dot blot molecular hybridization. In this method CCCVd is amplified by the PCR (polymerase chain reaction) and the clones of CCCVd are used as templates to synthesize a complementary DNA or RNA chain. These sequences are radioactively labelled so when they are put over the samples with the intention to analyse (on a supporting membrane) and exposed to x-ray film, then if CCCVd is present it will appear as a dark colour. This dark tonality only appears when nucleic acid hybridisation occurs. Coconut cadang-cadang disease has no treatment yet. However chemotherapy with antibiotics has been tried with tetracycline solutions; antibiotics failed trying to alter progress of the disease since they had no significant effect on any of the studied parameters. When the treated plants were at the early stage, tetracycline injections failed to prevent the progression of the palms to more advanced stages, nor did they affect significantly the mean number of spathes or nuts. Penicillin treatment had no apparent improvement either.  Control strategies are elimination of reservoir species, vector control, mild strain protection and breeding for host resistance.[18] Eradication of diseased plants is usually performed to minimize spread but is of dubious efficacy due to the difficulties of early diagnosis as the virus etiology remains unknown and the one discovered are the three main stages in the disease development. Coconut Cadang Cadang Viroid (CCCVd) can be confused with another viroid called Coconut Tinangaja Viroid (CTiVd). That is because both viroids have 64% of their sequence of nucleotide in common. They both affect coconut palm, and infected plants have similar symptoms: spots on the leaves reduced top, yellow palms and even death. This article in anim agro technology refereed to various article from Philippine Coconut Authority Report, Wikipedia, CABI and Department of Agriculture, Malaysia. Thanks. Semuga artikel ini memberi info berguna kepada semua para pembaca blog anim agro technology kali ini. Wasallam...

By,
M Anem,
Senior Agronomist,
Precint 3, Putrajaya,
Federal Territory,
malaysia.
(18 JamadilAwal 1440 Hijrah).

Updated on: 28 September 2022.