General characteristics of the virus

Virus (Virus) is a kind of idiopathic parasite, which is much smaller than bacteria. Its size is generally about 10~30um and can not be seen under ordinary light microscope. The virus has the structure of cell wall and nucleus, which is fibrous, rod-shaped and so on. In general, some viruses can be extracted into crystals from the plant. Under the electron microscope, there are very neatly and tightly arranged virus particles in the virus crystals.

The virus consists of nucleic acid and protein. Most of the nucleic acids of viruses parasitic on Chinese orchid plants are ribonucleic acid (RNA). The nucleic acid of the virus is coated in the shell of a protein. When the virus infects the cell, only the nucleic acid enters the plant cell, while the shell of the protein is left in vitro. Therefore, it is only the nuclear protein part that has infectivity, and its pathogenicity is mainly determined by its nucleic acid part. A virus can have two different forms. Particles with different morphology may have different genetic division of labor. Only when the particles of different forms enter the strange host together, can they show all the infectivity, pathogenicity and other genetic characteristics of the virus.

The virus of orchid has a high ability of proliferation. The mode of proliferation is different from that of cellular organisms. Instead of absorbing nutrients in parasitic cells to form a large virus and then dividing into a small virus, it uses RNA to replicate. Under the control of viral nucleic acid, the host cell synthesizes the same substance as the nucleoprotein of the virus to form a new virus. The harmfulness of the virus also lies in changing the metabolic pathway of parasitic cells and destroying normal physiological procedures. In orchids, the virus seems to destroy the chloroplasts in the cells, resulting in chlorosis of the cells, causing disorders in the assimilation of nutrients in the cells, and yellowing or necrosis of leaf tissues. It is necessary to further study whether the virus particles directly act on the cells or the toxins released by the virus.

At present, it has been confirmed that orchid virus diseases include orchid mosaic virus CymHdium mosic virus and tooth orchid ringspot virus Odontoglossum ring spot vlrus. (Liu Zhongjian)