Etiology, distribution and control of virus-like diseases of coconut palm in th south Pacific.

• Department of Agriculture, Vanuatu

Research in this project aims to identify the causal agent of foliar decay transmitted by Myndus taffini (FDMT). The disease - seen since 1965 in Vanuatu but only on introduced coconut varieties - causes different symptoms from those of other wilts: first the middle leaves turn yellow, then diseased palms usually die within 2-4 years. While the local 'Vanuatu tall' variety is resistant, the disease severely affects potentially high-yielding hybrids or cultivars, such as yellow Malayan Dwarf, preventing their introduction for breeding or planting programs. A current government replanting program is confined to Vanuatu tall, although a seed garden has been established to provide Vanuatu tall x Rennel tall hybrids, which show some tolerance and have 30% better production than the local trees.

Myndus spp. similar to M. taffini occur in islands of neighbouring countries in the South Pacific. Islands where no introduction of FDMT-susceptible cultivars has been attempted may have similarly resistant local palms, so the distributlon of the wilt remains unknown.

Accordingly, this project seeks to determine the etiology of foliar decay induced by Myndus taffini on coconut palm in Vanuatu, to deve1op diagnostic tests and to deternine the distribution of the disease in the South Pacific.

Work in Vanuatu will concentrate on transmission of foliar decay and on other biological aspects, and work at the Waite Institute will be directed towards identifying a virus or virus component associated with it. Preliminary results suggest that at least two types of virus-like particles may be associated with the disease, but neither has yet been implicated. Furthermore, unusual high-molecular-weight RNAs have been found in a diseased sample.

Etiological studies will use mainly electron microscopy, analysis of nucleic acids by gel electrophoresis, serology and molecular hybridisation. Electron microscopy will be used to seek virus-like particles, and techniques now in routine use for isolating nucleic acids from coconut palms will be applied to a range of samples to determine any correlation between the disease and the unusual RNA components found already.

Scientists in Vanuatu and Australia will seek to develop diagnostic tests. If successful, they will use the tests for: developing inoculation techniques to confirm pathogenicity and host range studies; epidemiological studies on host range, distribution, and rate, range and time of spread of the presumed pathogen; detecting tbe putative virus in vectors and studying virus-vector associations sucb as acquisition, persistence and parameters of inoculation; and testing possible control measures such as eradication, barriers, resistance and vector control.

A successful diagnostic test would also allow the team to use sampling and assays to determine the distribution of the disease in the South Pacific.

While previous research has shown that the disease does not involve the cadang-cadang viroid, other aspects of the related ACIAR Project 8402 on that topic, under the same leader, may have relevance in the diagnosis and distribution studies. Together, the two projects should provide considerable protection for this important crop of the Pacific region and in the Philippines.