Poinsettias (Euphorbia pulcherrima) with distorted growth and light green mottling amongst leaves and bracts were observed. This Alert describes and provides photos of symptoms caused by poinsettia mosaic virus (PnMV) on poinsettia. To diagnose PnMV, submit whole plant samples to your preferred diagnostic lab.
Poinsettia Mosaic Virus (PnMV)
Poinsettia mosaic virus (PnMV) is a pathogen that has been sporadically reported worldwide over the last 40 years, including reports from Canada (Daughtrey et al., 1995), the United States (Fisher and Bell, 2013), Mexico (Ocampo et al., 2013), Venezuela (Carballo et al., 2001), Norway (Blystad and Fløistad, 2002), Australia (Gordon et al. 1996), and New Zealand (Lebas et al., 2007). The host range of PnMV is limited primarily to Euphorbia sp., of which poinsettia (E. pulcherrima) is most susceptible to infection (Daughtrey et al., 1995; Haenni and Dreher, 2008). Depending on the severity of PnMV symptom expression, infected poinsettias could be deemed unmarketable, which would pose major implications to greenhouse growers.
Transmission
While PnMV has not been reported to have any known vectors, other members of the family of viruses to which PnMV belongs, Tymoviridae, are commonly transmitted via sap by flea beetles (Chrysomelidae: Alticinae; Daughtrey et al., 1995). Since the virus is transmissible via sap, this means that mechanical transmission is possible and that direct contact between infected plant tissue and healthy plants could cause infection. Poinsettia mosaic virus is not transmissible through seeds or pollen (Haenni and Dreher, 2008), and it is unlikely that the virus is transmitted through the soilless substrate (Blystad and Fløistad, 2002). For the infected poinsettias observed, all symptomatic plants presented onset of symptoms around the same time, which would suggest that the virus was introduced to all plants simultaneously (i.e., during propagation). These poinsettias were grown under temperatures of 18°C day/ 20°C (65°F day/ 68 °F night), which could have led to more pronounced mottling and distortion than would have occurred under warmer greenhouse conditions.
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