Studies on Cadang Cadang disease of coconut in the Philippines in Micronesia

• Department of Resources and Development, Federated States of Micronesia
• Philippine Coconut Authority, Philippines

Cadang-cadang disease has killed some 30 million coconut palms in the Philippines since it was first recorded there about l918, making it one of the most serious diseases of coconut in the world. In 1973, Dr J. Randles of the Waite Institute and his colleagues discovered the viroid causing the disease during a collaborative program involving the Waite Institute, the Philippine Coconut Authority and FAO/UNDP. In the ensuing 10 years, that program has: developed methods of mechanical transmission; developed diagnostic methods based on polyacrylamide gel electrophoresis and molecular hybridisation; demonstrated that other palm species are susceptible to infection with the viroid; detected the viroid in Guam; and sequenced the viroid. However, it will shortly conclude, and this project will continue the investigations as soon as collaboration arrangements are finalised.

Discovery of the viroid in Guam and its recent tentative identification in the North Mariana and Caroline Islands indicates the widespread importance of the disease. Interestingly, the symptoms found in Micronesia differ from tbose reported in the Philippines, suggesting the possibility of finding mild strains of the viroid or resistant or tolerant coconut cultivars.

The project has four main objectives. Since control strategies will ultimately depend upon the solution of this major problem, determining the mode of natural spread of the viroid has some priority. Standard surveys in areas of high incidence and at boundaries of distribution will determine the rate and range of disease movement. Early indications suggest that pollen may carry the viroid, and field trials will test this possibility. Its distribution patterns will be studied in Micronesia, to compare them with patterns in the Philippines and to determine whether site affects the epidemiology of the disease.

Since such disease surveys rely heavily on diagnosis, the second objective is to improve the speed, sensitivity and reliability of the diagnostic procedures. Present procedures use bi-directional gel electrophoresis combined with sensitive silver staining and hybridisation analysis. Modifications are constantly being attempted, particularly for use in surveys where facilities are limited. Much of this research will take place in the Philippines.

In a third objective, the scientists will seek suitable coconut breeding material and test it for resistance to the viroid. To this end, they will improve inoculation procedures by determining optimum test plant ages and pretreatments, inoculum preparation and inoculation methods.

As their fourth objective, the scientists will seek biological variants of the viroid and purify and sequence these to detect sites of variation in the molecule that may determine pathoEenicity. They will use any mild variants that emerge from this work in interference experiments to test tbe possibility of mild-strain protection.

An associated project under the same leader - ACIAR Project 8403 - also concerns coconut diseases and may have relevance in the distribution and diagnosis studies. Together, the two projects should provide considerable protection for this important crop of the Philippines and the Pacific Islands.