Orchid Disease With Mottling on Dendrobium Leaves

Orchid Viruses

• Approximately 30 viruses attack orchids around the globe, according to the American Orchid Society website. Undetectable to the human eye, these microscopic organisms ruin an orchid's ornamental value by discoloring its leaves and flowers. They also weaken the plant, lowering its defenses against other diseases and environmental stress. Viruses consist only of nucleic acid enclosed in a protective protein sheath. After a virus penetrates a dendrobium's cell walls, it takes over the cell's reproduction and makes copies of itself. An orchid's cell walls, however, are too strong for a virus to penetrate on its own. For that, it needs damaged dendrobium tissue or orchid-feeding insects.

Spread

• Insects and unsanitary pruning tools all transport the orchid fleck virus. Mites, thrips, mealybugs and aphids all suck virus-contaminated fluids from a dendrobium's leaves and tender tissues, transferring it to the next plants they attack. The false spider mite (Brevipalpus californicus) transmits the disease in both its nymphal and adult stages. The mite remains infectious for as long as three weeks.

Symptoms

• Dendrobiums with orchid fleck virus develop mottled, yellow patches or stripes on their green leaves. In some cases, the patches have dead, brown centers or margins. Because the symptoms mimic those of fungal or environmentally related diseases, testing is the only way to verify the virus.

Identification

• Tests to identify OFV study infected plant tissue under an electron microscope and the ELISA, or enzyme-linked immunosorbent assay. In this test, the researcher places sap from a dendrobium orchid suspected of having the virus in a plastic tray with wells. The wells' surfaces collect virus proteins. After rinsing the tray with water, the researcher adds an enzyme-amended OVF antibody to the wells. Because virus protein has already coated the wells, only traces of the antibody will stick to them. After rinsing the tray a second time, the researcher adds a transparent dye that the enzyme from the antibody splits and colors. The depth of color indicates how much OFV is present in the dendrobium's sap.

Management

• The best OFV management option is to isolate any dendrobiums showing symptoms of the disease for testing. Keeping the isolated plants separated is essential. Otherwise, non-infected orchids with OFV-like symptoms are in danger of contracting the actual virus. Destruction of OFV-positive plants is the only way to control the virus' spread. Preventive measures include using the appropriate insecticides to control OFV-transmitting insects and sanitizing tools in a 5 percent sodium triphosphate solution for five minutes after working on each plant.