Detailed Explanation of the Infection Cycle of Viral Diseases

Viruses are intracellular parasites. They neither have the ability to break down plant cell walls, nor can they, like other parasites with saprophytic ability, live saprophytically on dead cell tissues as a transitional phase of parasitism. Therefore, when a virus invades an orchid, a slight wound is required. Such a wound must be able to cause damage to the cell wall without causing massive cell death. In this way, the virus can immediately come into direct contact with living cells and further proliferate and spread within the cells. Duringorchidcultivation, such slight wounds may come from abrasions when diseased and healthy plants touch each other, or from punctures by insects, especially those with piercing-sucking mouthparts, or from artificial pruning and mechanical injury. After the virus enters a living cell, it can only spread passively through the host's transport mechanisms. When it is in the parenchyma tissue, it spreads very slowly from one cell to another. But once it reaches the phloem, it begins to move rapidly with the plant's fluid flow. The time from virus invasion of the orchid plant to the onset of disease is generally relatively long. According to estimates, the incubation period of Cymbidium mosaic virus infecting the host is about 30 days in summer at 30 degrees, and about 20 days in winter at 15 degrees; the in vitro survival period is 60 to several days, and the thermal death point is 60 to 80 degrees. The incubation period of Odontoglossum ringspot virus infecting the host is about one week, the in vitro survival period exceeds 763 days, and the thermal death point is greater than 93 degrees. There have been no reports to date that airflow, water flow, and rainwater, the main driving forces for the spread of fungi and bacteria, play a role in the spread of viruses. Most are transmitted by insect vectors. Occasionally, they can also be transmitted by contact and friction between healthy and diseased plants. The insects that transmit viruses are mainly species with piercing-sucking mouthparts, among which aphids and leafhoppers are especially important. Scale insects are also worth suspecting. Some believe that nematodes can also transmitOrchidsThe incubation period of leaf virus infection and parasitism is about 30 days in summer at 30 degrees, and about 20 days in winter at 15 degrees. The survival period outside the body is 60 to several days, and the lethal temperature is 60 to 80 degrees. The incubation period of Odontoglossum ringspot virus infection and parasitism is about one week, the survival period outside the body exceeds 763 days, and the lethal temperature is greater than 93 degrees. At present, there have been no reports that the main driving forces of fungal and bacterial transmission - airflow, water flow, and rainwater - play a role in the spread of viruses. Most rely on insects as vectors for transmission. Occasionally, it can also be transmitted through contact and friction between healthy and diseased plants. The insects that transmit viruses are mainly species with piercing-sucking mouthparts, among which aphids and leafhoppers are especially important. Scale insects are also worth suspecting. Some people believe that nematodes can also transmitorchidviruses. Viruses can remain viable within the insect body for a long time; as long as the insect feeds once on an infected plant, it can transmit the virus over the long term, or even for its entire life. Viruses can continuously proliferate within the insect vector's body, and can even be passed on to their offspring as the insects reproduce. Viruses are mainly concentrated in the salivary glands of insects. When the insect feeds, the virus enters the plant body along with the saliva, thereby infecting the orchid plant. Duringcultivation, due to division of clumps, pruning of roots and leaves, pruning tools carrying viruses and spreading them to each other is also a major pathway for the occurrence of orchid viral diseases. There is no doubt that the sources of viral diseases are mainly living host plants and insects. Once an orchid plant is infected with a virus, the virus will survive in the plant body for a long time, unless the orchid plant dies or is artificially destroyed. (Liu Zhongjian)