Coconut foliar decay virus
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Coconut foliar decay virus (CFDV)
The virus causes a lethal disease of most foreign coconut cultivars (e.g. the Malayan Red Dwarf variety) in the islands of Vanuatu. It is transmitted by the planthopper Myndus taffini which breeds on the roots of Hibiscus tiliaceus (Wefels et al., 2015). Both the virus and its vector have been only recorded from Vanuatu. The native coconut variety (Vanuatu tall variety) is resistant to the disease, although it might carry the virus and show mild symptoms of the disease (see illustration below). The virus particles are icosahedral with a diameter of 20 nm and a single-stranded DNA genome with a length of 470 nm and approximately 1300 nucleotides.
The symptoms of the disease are characterized by a decay of the base of the older fronds. This starts with a lesion at the frond base (see illustration below) which expands, develops into a rot and causes the frond to collapse, dry up and hang down. In addition, susceptible coconut varieties can develop severe yellowing as well as necrotic and barren infloresecences which bear residual older nuts but no new nuts.
H. tiliaceus is the only known breeding plant for the vector M. taffini, where the nymphs live on the roots and suck plant juice. The adults feed on coconut palms and transmit CFDV in a persistent-circulative manner. Management of the disease is directed at removing H. tiliaceus plants from coconut plantations and breeding for resistant coconut cultivars by crossing native resistant varieties with high yielding foreign cultivars.
- Other images of the coconut foliar decay virus (John W. Randles, University of Adelaide, Australia - click to enlarge)
Malayan Red Dwarf coconut variety showing early decay symptoms at the base of a frond
Malayan Red Dwarf coconut variety with advanced decay symptoms at the base of a frond
Young coconut palms (Malayan Red Dwarf variety) showing symptoms of infection by the coconut foliar decay virus (left). The palms were inoculated with the vector Myndus taffini. Uninoculated palms on the right for comparison.
Malayan Red Dwarf coconut palm variety in Vanuatu, naturally infected by the coconut foliar decay virus
Malayan Red Dwarf coconut variety in Vanuatu naturally infected with the coconut foliar decay virus and showing advanced disease symptoms
Native "Vanuatu Tall" coconut variety. This variety is naturally resistant to the coconut foliar decay virus. However, this palm carries the virus and shows mild symptoms like collapse of older fronds
CFDV particles (20 nm in diameter) visualised after negative staining (upper) or shadowing (lower), scale bar = 50nm, inset on upper part is a circular ssDNA molecule
EM image of CFDV particles after shadowing
