Symptoms and control methods of orchid ringspot disease

1. Damage: distributed in the United States and various European countries, and commonly occurring throughout China. In China, the infection rate of Odontoglossum ringspot virus is higher than that of Cymbidium mosaicorchidleaf virus. The maincultivatedorchidsaffected are: Cattleya,Cymbidium ensifolium, Dendrobium, Odontoglossum, Epidendrum, Vanda, Phalaenopsis,Cymbidium sinense, large-floweredCymbidium faberi, Doritis, Eria, Oncidium, etc. Previously, tests for virus carriage were carried out on 15O species of wildorchidsfrom around the world, proving that wild orchids are not infected by the virus. But in recent years, large numbers of severely diseased plants have been found in wildCymbidium goeringii、Cymbidium sinenseproduced in Fujian. 2. Symptoms: This viral disease damages many kinds of orchids, forming various spots, and in severe cases the leaves wither and yellow and fade in color. Inoculation tests on Odontoglossum showed: on older inoculated leaves, small necrotic spots or ringspots appear; on somewhat younger leaves, light green to light yellow round, oval or diamond-shaped lesions appear. These lesions may be relatively distinct, with diameters ranging from 0.5 to 2 cm; within a few days after the first chlorotic symptoms appear, the edges of the infected parts turn yellow, while the internal tissue often remains light green. Within a few weeks after the first symptoms appear, the outline of the ringspot may partially or completely become necrotic, while its middle part still remains light green or light yellow. In some cases, the entire diseased area described above becomes necrotic, and water-soaked areas appear on the underside of the leaf. Necrotic lesions usually appear singly, but some also appear as several brown to black ringspots clustered together, with the tissue between them turning yellow, and the central lesion necrotic or remaining normal. The lesions are sometimes separated from one another by necrotic tissue, and sometimes they also overlap to form larger compound symptoms. OnCymbidium sinense, brown concentric rings with a wheel-like pattern appear, evenly distributed on the leaf; 4 to 5 months after symptoms appear, the entire leaf gradually withers and yellows and dies, and sometimes brown wheel-like patterns shaped like "/\" also form on the leaf, arranged in layer upon layer like a pagoda. OnCymbidium ensifolium, mosaic symptoms form; on inoculated leaves of Cattleya, necrotic spots are produced, while other non-inoculated leaves form mosaic. 3. Pathogen: The pathogens causing orchid mosaic virus are generally the following three: Orchid strain of tobacco mosaic virus,Cymbidium ensifoliumringspot virus and Epidendrum leaf spot virus. Orchid strain of tobacco mosaic virus (TMV-O) is also called Odontoglossum ring spot virus (ORSV). The virus particles are rod-shaped, 300nmX18nm, and some have also reported shorter particles of 18Onm; it belongs to the tobacco mosaic virus group. The particles are dispersed in the cytoplasm in a crystalline arrangement, the inclusion body is the "X" body, the sedimentation coefficient is 211.6S, A260/280=1.13, the nucleic acid is single-stranded RNA, molecular weight 2X1O6, the thermal inactivation point is 88 to 93 degrees C, though some have also reported 7O to 75 degrees C, the dilution end point is 10-5 to 1O-6, and the longevity in vitro at 18 degrees C is more than 1 year. This virus has a relatively close serological relationship with TMV cucumber green mottle mosaic virus (CGMV). Cymbidium ensifolium ringspot virus particles are spherical, isometric, diameter 28um, thermal inactivation point 85 degrees C, dilution end point 10-5, longevity in vitro below O degrees C is 3 months. The virus can infect Chenopodium murale, producing localized ringspots, and on Cymbidium ensifolium causes light yellow chlorotic spots and strip-shaped necrotic spots. Epidendrum leaf spot virus, particles filamentous, 25OnmX13nm, thermal inactivation point 50 to 55 degrees C, longevity in vitro 4 to 8 days. The virus produces obvious mosaic and chlorotic ringspots on Epidendrum. 4. Disease characteristics: The virus is transmitted through sap and contact; whether there is a vector insect is still unclear, and it is mainly transmitted by contaminated pots and irrigation water. Among these, ORSV is very stable, with a thermal inactivation point that can exceed 9O degrees C, and virus particles in diseased leaf sap can remain infectious for more than 10 years. This is a relatively stubborn virus, and once disease occurs it is difficult to eliminate. 5. Control methods: (1) For some valuable virus-free orchids, they must be isolated from orchid production bases forcultivation; for horticultural operations such as division and repotting, the fingers and tools must be disinfected again for every plant planted; roots cannot be washed in the same container, and running water should be used to wash roots; the media used forcultivating orchidflowers, such as peat, moss and gravel, should be disinfected. (2) Special attention should be paid to sanitation management and sanitary operations, with emphasis on the disinfection and removal of pots, media and plant residues. (3) Smoking and casually discarding cigarette butts are strictly prohibited during horticultural operations. Liu Zhongjian