Symptoms and diagnosis of orchid virus disease

Orchid virus disease has many remarkable characteristics in symptoms. It is a systemic infection disease. As the virus spread from the infection point to the whole body of the plant, the symptoms gradually appeared in all parts of the forest. Because orchids can propagate asexually, the nutrient exchange between branches is basically independent except for the new bud growth period. once one ramet is infected with the disease, it is unlikely to be passed on directly to another branch. but it can be passed on to new individuals formed by new buds from infected branches. The symptoms of orchid virus disease were the most obvious when the new leaves and leaf beetles contacted the growing leaves. Symptoms sometimes show up in flowers. Although there is a virus in the pseudocorm and root, it rarely shows the symptoms of injury. As the orchid virus disease has the above characteristics, the symptoms of mature strains infected with the virus are not obvious or even do not show, but after sprouting, the symptoms will be quite obvious on the new leaves. At this time, some people will remove the new buds showing symptoms and sell the asymptomatic old plants as plants without virus disease, so pay attention to the transaction.

Two types of symptoms of orchid virus disease have been observed:

Yellowing mottled orchid virus disease will appear in the leaves sooner or later. The main reason is the halo-like chlorosis in the leaves, gradually yellowing, and the perimeter of the markings is not clear. In these mottled contents, it is easy to infect other fungal diseases and produce compound infection, which is a bit like the harmful symptoms of leaf miner. The appearance of small infected tissue is normal.

The mottled or linear tissue died in the leaves of the orchid plants infected by the disease, and the depressions occurred on the back of the dead leaves, resulting in obvious transparent white spots, which caused the leaves to twist and atrophy by thinning the mesophyll tissue in the dead spots, resulting in serious leaf cracking.

The symptoms of the virus are easy to show symptoms in high temperature in summer, especially in the case of poor ventilation at high temperature, the symptoms are most likely to occur near the leaf beetle in the growing leaves. Of course, it is also easy to show symptoms in the young leaves of the new budding stage. Therefore, orchid virus disease is obvious at high temperature, but not obvious or hidden at low temperature. The onset of the disease is obvious in the early stage, but not obvious or occult in the later stage. When the symptoms appear, they will exist forever, but as the leaves grow or mature, the symptoms are masked and appear to be "alleviated".

Virus infection will not cause the whole leaves of orchid plants to die, and there is no death of orchids caused by virus infection, which shows that orchids are a parasite of orchid virus.

There are no symptoms of orchid virus disease, which helps to distinguish the virus disease from other infectious diseases.

It is worth mentioning that the symptoms of orchid virus disease are often confused with physiological diseases, especially those caused by element deficiency and environmental pollution. The biggest difference between them is that the symptoms can not be eliminated after viral diseases, while physiological diseases often occur in patches, and the diseased plants may return to health after increasing nutrition and improving the environment.

The easiest way to determine whether the disease of an orchid plant is caused by a virus is to make a preliminary diagnosis through symptom observation. The method is to put Lanlin in strong light, from the direction of backlight, through the back of leaves to check whether there are chlorotic halo mottled or necrotic spots. The transmittance of the lesion is obvious and easy to identify. However, the virus symptoms of the line Yilan are in the middle of the main line, which can be judged by the contrast of the color. The line pattern is white or yellow with luster, the transmittance is not obvious, while the virus spot is withered and white without luster, the light transmission is obviously in contrast with the surrounding area, and there is a depression in the spot. Viral diseases can generally be identified by this method.

If possible, it can be observed by electron microscope or identified by serum reaction. (Liu Zhongjian)