| Species/Accession | Exp 1 | Exp 2 | |||
|---|---|---|---|---|---|
| 8 Months pi | 3 Months pi | 8 Months pi | 20 Months pi | 34 Months pi | |
| V. pompona–CR0018 | 4.40 ± 0.52 | 8.51 ± 0,82 | 6.26 ± 0.36 | 6.61 ± 0.98 | 3.28 ± 0.12 |
| V. pompona–CR0031 | 4.35 ± 0.49 | Nd | Nd | Nd | Nd |
| V. planifolia–CR0044 | 6.53 ± 0.04 | 8.17 ± 0.46 | 8.13 ± 0.64 | 10.4 ± 0.23 | 8.95 ± 0.46 |
| V. planifolia–CR0036 | Nd | 8.58 ± 0.12 | 8.31 ± 0.32 | 9.82 ± 0.70 | 7.90 ± 0.54 |
| V. tahitensis–CR0017 | Nd | 8.67 ± 0.14 | 8.43 ± 0.04 | 10.3 ± 0.31 | Nd |
| V. bahiana–CR0087 | 6.55 ± 0.08 | Nd | Nd | Nd | Nd |
| V. crenulata–CR0091 | 6.37 ± 0.15 | Nd | Nd | Nd | Nd |
Nd, Not determined.
CymMV cannot be reliably detected in vanilla on the basis of symptoms and therefore diagnosis has to be based on detection of the virus. Numerous and innovative molecular techniques have been described for CymMV detection, such as: quartz crystal microbalance-based DNA biosensors (Eun et al., 2002), immuno-capillary zone electrophoresis (Eun and Wong, 1999), DIG-labeled cRNA probes (Hu and Wong, 1998), antisera produced to recombinant capsid proteins (Lee and Chang, 2008), super paramagnetic beads (Ooi et al., 2006), TD/RT-PCR (Seoh et al., 1998), rapid immunofilter paper assay (Tanaka et al., 1997), and wash-free antibody-assisted magnetoreduction assays (Yang et al., 2008).
Since CymMV particles are highly immunogenic (Francki, 1970) and abundantly and evenly distributed in host tissues (Lawson and Hearon, 1974; Leclercq-Le Quillec and Servé, 2001), serological techniques, such as ELISA or DIBA, which are cheap and robust, are particularly suitable for routine diagnosis of the virus. As would be expected from the low amino acid divergence of the CP, monoclonal as well as polyclonal antibodies have detected a wide range of isolates (Lee and Chang, 2008; Vejaratpimol et al., 1998; Wisler et al., 1982). However, Read et al. (2007) reported a strain (Thailand 306) that did not react with a commercial monoclonal antibody. This strain was characterized by aspartic acid instead of asparagine in position 123 of the CP, unique to this isolate.
More specific and sensitive detection of the virus can be achieved using nucleic acids-based methods, and a number of primer pairs and various formats have been designed for RT-PCR detection of CymMV (Barry et al., 1996; Bhat et al., 2006; Lim et al., 1993b; Martos, 2005; Ryu et al., 1995; Seoh et al., 1998; Yamane et al., 2008).
Epidemiology
CymMV incidence in vanilla plots was assessed in several surveys conducted in various agronomic conditions and revealed very disparate situations, not explicable by sampling bias alone. In Comores, for instance the entire planting material seems to be healthy since a recent and extended survey did not find a single virus infected vine (Grisoni and Abdoul-Karime, 2007). In Madagascar, the situation was similar at the beginning of 2000s with the large majority of traditional farmer plantations being CymMV free. However, most of the cuttings from new cultivars propagated in the germplasm repository at Ambohitsara (Antalaha district) were infected (Grisoni et al., 1997; Leclercq-Le Quillec and Nany, 1999, 2000). In Reunion and Society Islands relatively high CymMV incidence was recorded after intensive cultivation programs were initiated in the 1990s (Benezet et al., 2000; Grisoni et al., 2004; Leclercq Le Quillec et al., 2001) and epidemiological analysis could trace back the propagation of the virus in vanilla plots.