RT-PCR Detection of Odontoglossum ringspot virus, Cymbidium mosaic virus and Tospoviruses and Association of Infections with Leaf-Yellowing Symptoms in Phalaenopsis

Leaf-yellowing symptoms in Phalaenopsis are most important effects in its commercial production in Japan and their cause has not yet been clarified. In the present study, Odontoglossum ringspot virus (ORSV), Cymbidium mosaic virus (CymMV) and tospoviruses were evaluated by reverse transcription-polymerase chain reaction (RT-PCR) in Phalaenopsis showing leaf-yellowing symptoms. Ring, spot, mosaic, necrosis and other symptom types were observed in 42%, 24%, 25%, 16% and 44% of the tested plants respectively. ORSV was detected in 55% of the plants, particularly in 35 of 42 plants with ring symptoms. CymMV was detected in 34% of the plants, particularly in 18 of 25 plants with mosaic symptoms. Plants co-infected with both viruses tended to show severe symptoms. In spite of systemic infection by inoculation of ORSV, no clear ring symptoms were observed in any plant for 6 months. Symptoms of leaf-yellowing were significantly reduced after 3 months. These results suggest that the symptoms can be associated with the viruses but occurred and alleviated over time and by changes in the environmental conditions. No tospoviruses were detected in 70 tested plants. ORSV and CymMV were simultaneously detected by RT-PCR using reported primers for ORSV and newly designed primers for CymMV using an efficient direct tube RNA extraction technique providing more cost-effective RT-PCR screening. No viruses were detected by RT-PCR in several plants showing spot or ring symptoms, suggesting the presence of other causal agents related to these symptoms