Orchid viruses

MANILA, Philippines - Some of the most devastating pests in orchid culture are caused by virus infections. Viruses weaken the plants; shortens floral vaselife; produce unsightly and unmarketable flowers and plants.

It was stated by University of Hawaii orchid researchers that clean stocks of Dendrobiums used in cutflower production will acquire and accumulate viruses within 5 years of open field production.

 Seed-grown stocks are generally believed to be free from viruses. It is theorized that the placental tube of orchid seeds are too small to allow virus particles through. This is basically the reason why the University of Hawaii through the funds of Dendrobium Orchid Growers’ Association (DOGA) uses amphidiploid (polyploidy of heterozygous cross) seed lines for cutflower production. The university keeps the breeder stocks and does the seed production while the cutflower growers and accredited propagation nurseries order their seeds or young stocks from the university. The university gets a certain amount of royalty from plant sale to finance future orchid researches. Only the University (UH) can produce the UH series of cutflowers and pot plants.

The virus normally travels through the vascular system of the plants. This is basically the reason why viral lesions are usually arranged in straight lines or interveinally. Symptoms may include spots or linear chlorosis (loss of chlorophyll, therefore cells either light green colored or white/yellow); sunken areas and necrotic (dead cells) spots or areas on the leaves. 

In advanced stage of infection, even the flowers are affected. Similar sunken bleached areas may occur anywhere on the flower and flower stalks. Another manifestation of viral infection is the change in colors where some areas become lighter while the adjacent areas become darker in irregular blotches. This is called “color-breaking”. Color Break is a definitive characteristic of viral infection/s. 

Plants may be infected with virus but may not show outward symptoms. The danger is that these asymptomatic plants serve as depository of the viruses in a collection.

The most common mode of transmission of viruses is through the use of cutting instruments (e.g. pruning shears, blades and knives). Insects are suspected also to be vectors of orchid viruses.

When virus is in the plant system, the only way to get rid of it is to isolate the small growing point through meristem tissue culture. The small group of cells that are actively multiplying believed to be free from virus are extracted and cultivated in artificial media. Plants produced from this methodology are virus free.

For cutflower production, plants should be provided with ample nutrition so that the vegetative growth can out grow the areas with high virus titer. Well nourished plants seldom show viral symptoms on young tissues.