Two New Hosts for Poinsettia Mosaic Virus.

Poinsettia mosaic virus (PnMV), a possible member of the genus Tymovirus, commonly infects the potted flower crop Euphorbia pulcherrima Willd. ex Klotzsch (1). Two new host species for this virus were identified during grafting experiments with E. pulcherrima and other Euphorbia spp. E. cornastra (Dressler) A. Radcliffe-Smith was reciprocally grafted with PnMV-positive E. pulcherrima cv. Eckespoint Lilo. PnMV was detected by double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) in E. cornastra leaves directly below the graft union 4 weeks after grafting. Infection was not fully systemic 6 weeks after grafting when screened by DAS-ELISA with antibodies specific to PnMV (DSMZ, Braunschweig, Germany). The symptomless infection in E. cornastra persisted in cuttings from grafted plants after a 1-year observation period. E. bubalina Boiss. anatomy differs from that of E. pulcherrima. The two species did not produce a viable graft union. However, in an experiment with two attempted graftings, the E. pulcherrima scions remained turgid for 14 to 18 days. As a result of one grafting, the E. bubalina rootstock tested positive for PnMV. The virus induced a mild mosaic in E. bubalina, but no reduction in growth. To confirm virus presence in E. cornastra and E. bubalina, both DAS-ELISA and immunosorbent electron microscopy were used. Non-grafted controls remained PnMV negative. PnMV was re-isolated from both species by sap inoculation to Nicotiana benthamiana. E. coulescens Haw., E. xylophyllides Brogn. ex Lem., E. marlothiana N. E. Br., and Ricinus communis L. were not infected by PnMV after similar grafting attempts. Reference: (1) A. A. Brunt et al., eds. 1996. Viruses of Plants. CAB Int., Wallingford, UK.