Diseases of Vegetable, Ornamental and Spice Crops

BACTERIAL AND VIRAL DISEASES

B) BACTERIAL DISEASES

5) Angular leaf spot
Symptoms:

• On leaves water-soaked spots delimited by veins appear (Plate-4).
• A crust of bacterial ooze is formed on them and dead tissue may drop off leaving shot holes.
• The spots on fruits are circular, brown to black and superficial.

Pathogen:

• The disease is caused by bacterium Pseudomonas syringae pv. lachrymans (Smith& Bryan) Young et al .
• It is Gram -ve, aerobic, non spore forming, straight rods, motile with 1-5 polar flagella.

Disease cycle and epidemiology

• The bacterium overwinters in infected seed as well as in plant debris.
• Optimum temperature for disease development is 20-24^o C and moisture is most important factor for disease development and spread.

Management:

• Follow crop rotation.
• Collect and destroy infected plant debris.
• Use disease free seed produced in dry areas and soak them in Streptocycline (100 ppm) for 30 minutes and dry them under shade before sowing.
• Spray the crop with Streptocycline (100 ppm) or copper oxychloride (0.3%) and repeat at 10 to 14 days interval.

C) VIRUS DISEASES

6) Cucumber Mosaic
Symptoms:

• Most strains of virus cause systemic infections, which are sometimes symptomless.
• The virus cause severe mosaic, mottling, chlorosis, necrosis and distortion in leaves and fruits.

Pathogen:

• The disease is caused by Cucumber Mosaic Virus which belongs to genus Cucumovirus.
• The particle size of virus is 29nm.

Disease cycle and epidemiology:

• The virus has wide host range including members of cucurbitaceae, solanaceae, malvaceae, brassicaceae and leguminosae.
• It is transmitted in non persistent manner by aphids like Myzus persicae and Aphis gossypii.
• The virus is also known to be transmitted mechanically and through seed.

Management:

• Planting barrier crops, applying sticky traps or covering the ground with an aphid deterrent material like aluminium foil boards can help in reducing the disease incidence.
• Use of virus free seed together with erradication of virus reservoirs are effective.

Other important diseases are: Bacterial wilt: Erwinia tracheiphila (Smith) Bergey et al.,
Seed rots and damping -off : Pythium aphanidermatum (Edson) Fitzp., Rhizoctonia solani Kuhn, Squash mosaic : Squash mosaic virus (Comovirus).