Diseases of Fruit Plantation Medicinal and Aromatic Crops

Red rust

Causal organism: Cephaleuros versicolor

• The algal disease and it has been observed in India and else where. It is one of the minor disease of importance. Reduction in photosynthetic activity and defoliation because of algal attack lower the vitality of host plant.
Symptoms

• The disease is initially characterized by green coloured, circular patches with marginal serrations.
• The upper surface of the spot consist of numerous, unbranched filaments which project through the cuticle.
• As the disease advances the organism forms red, rusty spots on the leaves and young twigs.
• Mature spores fall and leave cream to white velvet texture on the surface of the leaf.


Etiology

• The algae develop its reproductive structure after the vegetative growth.
• Certain cells become sporangia which are of two types.
• Those formed directly on the thallus are sessile and thick walled, 40-50 µm in diameter with orange pigments. They are formed singly on the vegetative filaments.
• Some are produced above the surface on special sporangiophores consisting of thick, rigid, septate of 50 µm in length, swollen into a vesicle at the tip. Each vesicle carries 3-6 sporangia on curved pedicels.
• When sporangia ripened, the contents are converted in to zoospores and liberated through an opening in the wall.
• The zoospores are orange in color, ovoid and swim actively by means of cilia.

Epidemiology

• The disease is more common on close plantation.
• The zoospores cause initial infection.
• High moist condition favours development of fruiting bodies of the algae.

Management

• It is controlled by spraying Bordeaux mixture (1% ) or Copper Oxychloride (0.3%) or lime sulphur(0.2%) on the trees