School of Biological Sciences,
The University of Auckland,
Private Bag 92019,
Dr Mike Pearson (SBS)
Dr Michel Grisoni (CIRAD/SDR, French Polynesia)
Dr Dan Cohen and Dr Dave Beck (HortResearch, New Zealand)
Vanilla is an orchid that is cultivated for its flavoursome beans used in the food and perfume industries. The broad aim of this collaborative research project between French Polynesia in the Pacific Ocean and Reunion Island in the Indian Ocean is to increase the knowledge on viruses infecting vanilla crops. This involves obtaining sequence data from the various virus isolates to be able to characterise the virus species as well as design specific detection assays for diagnosis purposes.
During the course of this research one of the worlds most widely distributed viruses, Cucumber mosaic virus (CMV) was detected for the first time in vanilla, and provided an original and interesting case for phylogenetic study. CMV had previously been divided into two subgroups I and II based on serological data and sequence similarity, with subgroup I being recently further divided into IA and IB after further phylogenetic analysis (Roossinck et al., 1999). CMV isolates from vanilla clearly belonged to subgroup I, but formed a cluster that was distinct from subgroups IA and IB, suggesting that CMV has evolved into a form that is adapted to the host vanilla.
This finding raised the following questions: (i) How do vanilla CMV sequences compare with those from other orchid species and is there an orchid-type of CMV? (ii) What are the origins of the vanilla strains of CMV? (iii) Since different CMV strains have different host affinities, what other hosts are susceptible to vanilla strains of CMV and do these act as a source of virus inoculum for vanilla crops? Further investigation into the phylogeny of CMV in vanilla in the Pacific and Indian Oceans will help answer these questions and provide information that is needed for effective disease management.
Roossinck MJ, Zhang L and Hellward KH, 1999. Rearrangements in the 5' nontranslated region and phylogenetic analyses of Cucumber mosaic virus RNA3 indicate radial evolution of three subgroups. Journal of Virology 73(8): 6752-6758.