Diseases of Vegetable, Ornamental and Spice Crops (2+1)

Bacterial Diseases

Bacterial wilt

Bacterial wilt is a limiting factor in successful cultivation of eggplant crop particularly in tropical, subtropical and some warm temperate climates. In hills, the incidence of this disease was high at intermediate elevations i.e. between 800 to 1400 meter m.a.s.l. and decreased with the increase in altitude. Symptoms, pathogen, disease cycle, epidemiology and management are same as described under tomato.

Little leaf

This is an important disease particularly in Southeast Asian countries where the activity of the vector is more.

Symptoms:

• The disease is characterized by reduction in leaf size which has shortened petioles and leaf lamina (Plate-2).
• There is production of more number of branches and all this results in stunted and bushy appearance of the plants.
• The flowers are not produced but in case these are produced, that remain green.

Pathogen:

• The disease is caused by Phytoplasma having ovoid or spherical body.
• These measure 40-300 nm in dia. and lack a rigid cell wall.
• The Phytoplasma are present in phloem sieve tubes.

Disease cycle and epidemiology:

• Phytoplasma perennates on weed hosts like Datura spp., Vinica rosea and several others.
• The disease is transmitted by grafting and through leaf hopper Hishimonas phycitis and Empoasca devastans but later is less efficient.

Management:

• Destruction of weed hosts from in and around the field and control of vectors through application of insecticides is advocated.
• Dipping of seedlings in tetracycline (0.05%) before transplanting followed by soil application of Phorate (1kg/ha) also keeps the disease under check.