Orchid ring spot

1. Harm: it is distributed in the United States and European countries, and is common in all parts of China. In China, the infection rate of tooth orchid ringspot virus is higher than that of orchid mosaic virus. The main cultivated orchids harmed by it are: Cartland, Jianlan, Dendrobium, Dendrobium, Magnolia, Magnolia, Phalaenopsis, Cymbidium, Oncidium and so on. In the past, 150 species of wild orchids from all over the world were tested for virus, which proved that wild orchids were not infected with the virus. However, a large number of seriously susceptible plants were found in wild Cymbidium and Cymbidium produced in Fujian in recent years.

2. Symptoms: the virus disease harms many kinds of orchids and forms many kinds of spots, and when the leaves are withered and yellow, the flowers fade. The inoculation test of tooth orchid showed that there were small necrotic spots or ring spots on the older inoculated leaves, and light green to yellowish, round, oval or diamond-shaped spots on the slightly young leaves. These spots may be relatively clear, and their diameters vary from 0.5~2cm. Within a few days of the first chlorosis symptoms, the edge of the infected site turns yellow, while its internal tissue often remains light green. Within a few weeks after the onset of the first symptom, the verandah of the ringspot will be partially or completely necrotic, and the middle part of it will remain light green or yellowish. In some cases, the entire part of the disease mentioned above will be necrotic and water stains will appear on the back of the leaf. Necrotic plaques usually appear singly, but some also have several brown to black ringed spots together, during which the tissue turns yellow and the central plaque necrosis or remains normal. The lesions are sometimes separated by necrotic tissue, and sometimes overlap to form larger compound symptoms. The brown concentric ring in the shape of a wheel on the orchid is evenly distributed on the leaves. After 4-5 months of symptoms, the whole leaf will gradually wither and die, and sometimes a "/\" brown wheel will be formed on the leaf, which is arranged like a pagoda on the leaves. Mosaic symptoms were formed on Jian Lan, necrotic spots were formed on Cartland inoculated leaves, and other uninoculated leaves formed mosaic.

3. Pathogens: there are three pathogens that cause orchid mosaic virus: tobacco mosaic virus orchid strain, Jianlan ringspot virus and tree orchid leaf spot virus.

Tobacco mosaic virus orchid strain (Orchid strain of tobacco mosaic virus,TMV-O) is also known as tooth orchid ringspot virus (Odontolossum ring spot virus,ORSV). The virion rod, 300nmX18nm, and the shorter particles of 18Onm have also been reported, which belong to the tobacco mosaic virus group. The particles were dispersed in the cytoplasm and arranged in a crystal lattice, the inclusion body was "X" body, the sedimentation coefficient was 211.6 S and 280mm 1.13, the nucleic acid was single-stranded RNA, the molecular weight was 2X1O6, and the lethal temperature was 883.93 ℃. It was also reported that it was 7O~75 ℃, the dilution end point was 10-5~1O-6, and the in vitro preservation period was more than one year. The virus had close serological relationship with TMV cucumber green mottle virus (CGMV).

Jilan ringspot virus is spherical, equiaxed, 28um in diameter, lethal temperature 85 ℃, dilution end point 10-5, in vitro preservation period less than O ℃ is 3 months, the virus can infect Chrysanthemum frutescens, produce local ring spots, light yellow chlorotic spots and strip necrotic spots on Jian Lan.

Magnolia leaf spot virus, granular line, 25OnmX13nm, lethal temperature of 50-55 ℃, in vitro preservation period of 4-8 days, the virus produced obvious mosaic and chlorotic ring spots on the orchid.

4. characteristics of the disease: the virus is transmitted through juice and contact. It is still unknown whether there are any mediators, mainly by pots with virus and irrigation water. Among them, ORSV is very stable, the lethal temperature can exceed 90 ℃, and the virus particles in the juice of diseased leaves can be preserved for more than 10 years. This is a relatively stubborn virus, which is difficult to remove once the disease occurs.

5. Prevention and control methods:

(1) for some valuable virus-free orchids, they must be cultivated in isolation from the orchid production base; in gardening operations such as ramets and turning pots, fingers and tools must be re-disinfected; washing roots cannot be washed in the same container and should be washed with running water; media such as peat, moss and gravel used for orchid culture should be disinfected.

(2) Special attention should be paid to hygienic management and operation, and attention should be paid to the disinfection and removal of pot media and plant residues.

(3) smoking and littering of cigarette butts are strictly prohibited during horticulture.

Liu Zhongjian