Causal Relationship Between Cucumber Mosaic Cucumovirus and Kava Dieback in the South Pacific. R. I. Davis, Former Junior Research Fellow, University of New England, Armidale NSW 2351 Australia. J. F. Brown, Associate Professor, Department of Botany, University of New England, Armidale NSW 2351 Australia; and S. P. Pone, Plant Protection Adviser, South Pacific Commission, Private Bag, Suva, Fiji. Plant Dis. 80:194-198. Accepted for publication 16 May 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0194.

The major constraint to kava {Piper melhysticum) production in the South Pacific is a dieback disease of previously unknown etiology. The development of a mosaic symptom on young leaves plus certain leaf growth distortions frequently precedes the dieback. Data are presented that show that cucumber mosaic cucumovirus (CMV) is either the direct cause of kava dieback or a significant component of a disease complex. Double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) showed that CMV is geographically widespread in kava plants with leaf and dieback symptoms throughout the four main kava-producing nations of Fiji, Vanuatu, Tonga, and Western Samoa. An isolate of CMV originally obtained from a die-back-affected plant caused similar dieback symptoms in 80% of mechanically inoculated kava plants. Aphid transmission was also demonstrated. CMV was not fully systemic in all mechanically inoculated plants. DAS-ELISA indicated that the virus was not always present in every stem on multi-stemmed plants and 56% of subsequent new stem growth was uninfected