Diseases of Fruit Plantation Medicinal and Aromatic Crops

Yellow leaf disease

Causal agent:Phytoplasma-like organisms (PLO's).
Symptoms

• Symptoms include yellowing of leaves and shedding of both mature and immature nuts. Endosperms of diseased nuts are soft, blackish and not suitable for consumption.
• Yellowing at the tips of leaf lets in 2or3 leaves of the outermost whorl is the first visible symptom.
• Brown, necrotic streaks run parallel to lamina in unfolded leaves, with the development of leaves, yellowing starts form the tips of leaflets, gradually extending to the middle of the lamina.
• One or two leaflets in any of the crown or the entire foliage may be affected by the disease. Tips of the chlorotic leaves eventually dry up.
• In advanced stages, leaves are reduced in size, become stiff and pointed, closely bunched and puckered. Finally the crown falls down leaving the base trunk.
• Root tips turn dark and gradually rot. Production of lateral root is reduced.
• Affected fruits fall down. Some of the palms exhibiting foliar yellowing may produce normal nuts and all nuts in the bunch may not show kernel discoloration.
• Blocking of xylem vessels of older leaves of diseased palms, degeneration of cortex and presence of tyloses in xylem are also noticed in diseased roots.


Management

• True Mangala seedlings and South Canara variety showed tolerance to this disease. The hybrid Saigon×mangala yielded max number of nuts with minimum disease intensity.
• Palms which received higher dose of potassium and magnesium recorded minimum disease intensity.
• Use of Chlorotetracyclin hydrochloride (Aureomycin) and tetracycline chloride (achromycin) through root feeding and stem injection had no ameliorative effect on the disease.