First report of Olive latent virus 2 in wild castor bean (Ricinus communis) in Italy

G. Parrella^1*, A. De Stradis² and C. Vovlas³

¹ Istituto per la Protezione delle Piante del CNR, Via Università 133, 80055, Portici (Na), Italy
² Istituto di Virologia Vegetale del CNR, Via Amendola 165/A, 70126, Bari, Italy
³ Dipartimento di Protezione delle Piante e Microbiologia Applicata, Via Amendola 165/A, 70126, Bari, Italy

 *parrella@ipp.cnr.it

Accepted for publication 08/05/07

Wild castor bean plants (Ricinus communis), showing bright yellow mosaic leaf symptoms were collected in Vibo Valentia (Calabria region, Southern Italy) during spring and summer of 2005 and 2006. Symptoms consisted of yellow speckled leaves with significant mottled areas; some leaves also contained an arabesque line pattern (Fig. 1). Electron microscope observations of sap extracts from symptomatic leaves showed semi-spherical to bacilliform particles consistent with Alfamovirus and Oleavirus (Fig. 2). Using a range of herbaceous plants and mechanical inoculation, a virus was isolated from castor bean; symptoms, in particular in Nicotiana benthamiana, N. clevelandii, N. occidentalis, N. glutinosa, Chenopodium quinoa, Phaseolus vulgaris cv. La Victorie and Gomphrena globosa, were comparable with those previously described for a castor bean isolate of Olive latent virus 2 (Grieco et al., 2002). The virus was identified serologically by particle decoration with an OLV2 antiserum, raised against an Italian OLV2 isolate (Fig. 2; Grieco et al., 1992), and by sequencing the movement gene (MP) and the coat protein gene (CP), as described previously (Grieco et al., 2002).

Figure 1: Comparison between leaves from healthy (left) and OLV2 infected (right) castor bean plant

The nucleotide sequence of a 1696 bp amplicon, encompassing the MP and CP genes, was determined (GenBank Acc. AM600639).  BLAST analysis showed 97% nucleotide identity with an OLV2/CB castor bean isolate from Greece (GenBank Acc. AJ439450) and 93% with the type isolate (GenBank Acc. X76993).  Deduced amino acid sequences identities for MP protein were 98% with OLV2/CB and 94% with the type isolate and 97% and 96% for the CP protein respectively. In both proteins, amino acid substitutions were mostly concentrated in the N terminus region.

Figure 2: Virus particles observed by electron microscope in leaf sap from symptomatic castor bean (A) and particles from the same sample decorated with the OLV2 antiserum (B). Magnification bar = 100nm.

Most aspects of the eco-biology of OLV2 are still unclear (e.g. vector transmission, isolate variability, natural host range). OLV2 was previously detected in wild castor bean in Greece (Vovlas et al., 2002); we have described in Italy a disease caused by another OLV2 isolate in the same host. This new finding might suggest a potential role of castor bean in the epidemiology of OLV2, by acting as a natural virus reservoir.

Acknowledgements

The authors would like to thank Ms Daniela Sorrentino for her excellent technical assistance.

References 

Grieco F., Martelli G.P., Savino V., Piazzolla P., 1992. Properties of Olive latent virus 2. Rivista di Patologia Vegetale 2, 125-136.

Grieco F., Parrella G., Vovlas C., 2002. An isolate of Olive latent virus 2 infecting castor bean in Greece. Journal of Plant Pathology 84,129-131.

Vovlas C., Parrella G., Di Franco A., 2002. Infezioni naturali del virus latente dell’olivo su piante di ricino in Grecia. Informatore Fitopatologico, 7-8:66-68.