Symptom Identification and Control Methods of Orchid Mosaic Virus Disease

[also known as Necrotic mosaic,orchidmosaic (Orchid mosaic), and Black streak (Blackstreak)] Distribution: Worldwide; common in southeastern China. Pathogen: Cymbidiumorchidmosaic virus (CyMV). Hosts: Extremely wide-ranging, with more than 70 genera, including Calanthe, Cymbidium, Dendrobium, Paphiopedilum, Phalaenopsis, Vanda, Vanilla, etc. Symptoms: They vary depending on the environment and the species infected. Usually, long strips of necrotic tissue appear on the lower leaf surface, causing leaf death, but the flowers may show no symptoms. In the early stage, there are irregular chlorotic mosaic patches. About 3 weeks after infection, chlorotic spots appear on new shoots of Chinese orchids, becoming more and more obvious and numerous as the leaves grow, and then turning into brown or dark brown necrotic spots. In some hybrids of Chinese orchids, rectangular, yellowed broken lines appear, followed by necrosis. Black necrotic areas may also spread over the entire leaf. In some varieties of Oncidium, brown or black sunken spots or even concentric rings appear on the lower leaf surface, with only a few spots on the upper leaf surface. In Phalaenopsis, the mosaic consists of light green and chlorotic patches, with deep grooves and ridges as well as water-soaked areas; necrosis on the lower surface is far more severe than on the upper surface, and it may also cause leaf death. Control: Controlling viral diseases mainly relies on removing diseased plants, improving sanitation, and disinfecting tools and other methods to prevent their spread. At present, the disinfectant solutions internationally recognized as relatively effective are: 1. A 2% formalin and 2% sodium hydroxide aqueous solution (it cannot be used once it turns green); 2. 164 g of anhydrous or 377 g of crystallized trisodium phosphate (Na3PO4) added to 1 L (1000 cc) of water. These can be used to disinfect tools, the environment, etc. (Chen Xinqi, Ji Zhanhe)