Diseases of Fruit Plantation Medicinal and Aromatic Crops

Black root disease

Black Root
Causal organism: Rosellinia arcuata Fetch.

• It is a common disease of tea occurring in India and Sri Lanka.
• The fungus is believed to originate usually in heaps of dead leaves and found at the top 5.0 to 7.5 cm layer of the soil, especially where there are dead leaves only.
• It spreads rapidly in the form of strands attacking roots of several other plants besides tea. The black strands closely adhere to the roots as loose cob-webby mass.
• The fungus enters the bark and spreads out into the star- like sheets of white mycelium which can be easily seen after peeling the bark of the larger roots.
• The attack usually begins at the collar region. In older tea bushes, it soon forms black strands closely attached to the root.
• The mycelium penetrates inside and ramifies between bark and wood. At each point of entry it divides into number of strands which radiate over the surface of the wood and form s a white star upto 1.0 cm in diameter.
• The pathogen has two types of fructifications, a conidial stage and a perithecial stage.
• Disease spreads to other parts of the field through conidia dispersed by the wind. Mycelium surrounds the stems near the surface of the soil and kills bark all round upto length of 7.5 to 10.0 cm.
• Consequently, a swollen ring of tissue is formed round the stem above the dead patch and below the latter.
• The conidia are borne on short bristle-like stalks.
• The perithecia are black, Spherical bodies about 0.5 to 1.0 mm in diameter. They bear asci which in turn bear ascospores.
• The disease spread by wind.