Diseases of fruit plantation medicinal and aromatic crops (2+1)

Bacterial blight

Causal organism: Xanthomas axonopodis pv. punicae
Symptoms

• Small, irregular, water soaked spots appear on the leaves.
• Spots vary from two to five mm in diameter with necrotic centre of pin-head size.
• Spots are translucent which turn light brown to dark brown after sometime and are surrounded by prominent water-soaked margins. Spots coalesce to form large patches.
• Severely infected leaves defoliated.
• The bacterium attacks stems, branches and fruits also.
• On stem, the disease starts as brown to black spots around the nodes .It further causes girdling and cracking of nodes. Finally the branches get broken.
• Brown to black spots formed on fruits which are raised and oily in appearance.

Etiology

• It is a Gram-negative rod, motile with single polar flagellum. It is non acid fast and aerobic.
• Mode of spread and survival
• The bacterium survives on the tree.
• The pathogen survives for 120 days on fallen leaves during the season.
• The primary infection occurs through infected cuttings.The disease spreads through wind and splashed rains.
Epidemiology

• High temperature and low humidity favour the disease. Temperature of 30 - 34° C and relative humidity (80 to 85%) is favourable for multiplication of the pathogen.
Management

• Clean cultivation and strict sanitation in the orchards help in reduction of disease incidence.
• Collect and burn the fallen leaves
• Spraying of 1 % urea solution on fallen leaves enhances their degradation process.
• Bleaching powder spray on the fallen leaves reduces the inoculum
• Spraying Bordeaux mixture (1.0%) controls the disease.
• Spray 0.05% streptocycline to control the disease
• Copper oxy chloride spray (0.3% concentration) can also be done.
• Pruning at correct stage would reduce the disease(Bahar pruning)
• Ganesh has been found to be a moderately resistant variety for bacterial blight disease