National orchid mosaic disease

[also known as necrotic mosaic disease (Necrotic mosaic), orchid mosaic disease (Orchidmosaic), black streak necrosis (Blackstreak))

Distribution: worldwide; common in southeastern China.

Pathogen: national Orchid Mosaic virus (CyMV).

Parasitism: there are more than 70 genera, including Calanthe, Cymbidium, Dendrobium, Paphiopedilum, Phalaenopsis, Vanda, Vanilla and so on.

Symptoms: vary depending on the environment and the type of infection. Long strips of necrotic tissue usually appear on the lower surface of the leaves, causing the death of the leaves, but the flowers can be disease-free. Irregular yellowish blotches in the early stage. About 3 weeks after infection, the new seedlings of Guolan appeared yellowish spots, which became more and more obvious and increased with the growth of leaves, and then became brown or dark brown necrotic spots. In some hybrids of Cymbidium, there are rectangular, yellowed intermittent lines, and then necrosis. Black necrotic areas may also spread throughout the leaves. In some varieties of Oncidium, brown or black sunken spots or even concentric circles appear on the lower surface of the leaves, while there are only a few spots on the upper surface of the leaves. In Phalaenopsis, the flower spots are light green and yellowing patches, with deep grooves, ridges and waterlogged areas, and the necrosis on the lower surface is much more serious than that on the upper surface, which may also cause the death of leaves.

Prevention and treatment: the control of virus disease is mainly to remove diseased plants, improve environmental hygiene, disinfect appliances and other methods, in order to prevent its spread. At present, it is internationally recognized that the better disinfectants are: 1, 2% formalin and 2% sodium hydroxide aqueous solution (which can no longer be used after turning green); 2, 164g anhydrous or 377g sodium phosphate (Na3PO4) with 1L water (1000cc). Can be used for disinfection tools, environment, etc. (Chen Xinqi, Ji Zhanhe)