Molecular evidence for a persistent-circulative association between Coconut foliar decay virus and its vector Myndus taffini

Coconut foliar decay virus (CFDV) is transmitted to coconut palms by adults of the cixiid plant hopper Myndus taffini . Larvae of this vector develop on the alternate host, Hibiscus tiliaceus , but the way in which the adults become infective has not been studied. We show by in situ hybridization that viral DNA is associated with gut and ovaries but to distinguish between semipersistent, circulative or propagative modes of transmission we looked for evidence of replication in the vector. Larvae raised from eggs laid on the roots of H. tiliaceus , and adults fed on infected coconut leaf, were tested for the presence of the replicative form of CFDV DNA by a single-primer sense-specific PCR assay which distinguishes between virion-sense and complementary-sense CFDV-DNA. We report that only the virion-sense form of CFDV-DNA could be detected in both larvae and adults whereas both senses, indicating the presence of the double- stranded replicative form of the virus DNA, were detected in infected coconut leaf. About 16 % of the larvae were virus positive by this assay. As the larvae had not had access to coconut palm and there was no evidence of virus replication in the larvae or adults, a persistent-circulative mode of transmission is proposed in which the virus is acquired from H. tiliaceus by nymphs and transmitted transstadially to adults. Confirmation of this hypothesis requires the susceptibility of H. tiliaceus to CFDV to be tested.E. Wefels, J.P. Moran, J.W. Randle

Detection and diagnosis of coconut foliar decay disease

La maladie du dépérissement foliaire du cocotier est d'une grande importance économique puisqu'elle attaque toutes les variétés et cultivars. Au champ, les symptômes se caractérisent par le jaunissement des feuilles en position 7 à 11 avant d'atteindre le méristème apical. Plusieurs techniques analytiques permettent de détecter le virus, à partir de la protéine de la capsule ou de l'ADN. Les principales techniques sont : PCR, test PAGE, test Dot blot, test d'hybridation ADNc ou ARN