Viruses in Orchids ( Grammatophyllums)

It was stated by Dr. Haruyuki Kamemoto, of the University of Hawaii at Manoa, that “Orchid plants placed in cultivation will eventually acquire viruses within 5 years. This is very true with the cutflowers varieties where the risk of infection is increased by constantly subjecting the plants to pruning and cutting of flower spikes using unsanitized cutting instruments.

Plant collectors are exposed to the same risks. You need only one infected plant to start the ball rolling. A truant insect takes a bite of the infected plant and transfer the virus in all the subsequent bites that it takes. Complication to this fact is that most viral infections in orchids are asymptomatic or it does not manifest any outward expression of the viral infections. Any plant that has been in cultivation for several years is a suspect.

Although definitive virus identification is done using elaborate laboratory techniques there are quite a few symptoms that are attributed to viral and viroid infections that home growers and commercial nurseries may use for management of their collections and breeding plants.

Some of the symptoms of viral and viroid infections in orchids are: flower malformation, spike crimping of floral stalk tips, chlorosis, necrotic spots arranged in concentric circular or linear manner.

Once the plant is infected with virus…there are only two practical ways to clean up the plants of the viruses. These are: meristem tissue culture and dry seed culture.

The theory goes that the virus travels through the vascular vessels so that the meristem should be free from viruses above the vascular vessels so that extraction of the meristem above the first leaf primordia is the standard. There should be no vascular vessels included in the explant.

Orchid seeds in the other hand may be set on virus infected mother plants. The theory is that the placental tubes of the developing orchid seeds are too narrow for the viruses to pass through. Only dry seed cultured plants and matured green pod cultured plants with loose seeds (without employing scrapping) may be considered virus free and that will need to be tested for virus later to be sure.

Even tissue cultured young plants may be suspect in harboring viruses. These usually result when the tissues extracted is bigger than necessary. The big necrotic areas may be bacterial or fungal but the singular chlorotic leaf in the lower half of the...

Viral lesions may arrange themselves in a concentric circle fashion and the necrotic lesions are arranged in concentric patterns, too.

The most common symptoms of viral infection is interveinal chlorosis. This symptom is for most cases misleading because it may be caused by herbicides, auxins or rooting hormones abuse and some other chemicals. When necrosis starts to appear right on...

Necrotic spots arranged in linear fashion is more definitive of viral infections.