Diseases of Vegetable, Ornamental and Spice Crops

VIRAL DISEASES

1. CAULIFLOWER MOSAIC
Symptoms:

• Vein clearing or banding symptoms are produced on the leaves ultimately leading to mosaic pattern (Plate-6).
• Only the young leaves are affected initially in which light green patches appear.
• Early infection may cause reduction in plant growth leading to stunted look.

Pathogen:

• The disease is caused by Cauliflower Mosaic Virus which belongs to caulimovirus (CaMV) group.
• Virions are isometric, 50 nm in dia. and non-enveloped and the genome consists of unipartite double stranded DNA.

Disease cycle and epidemiology:

• The virus is transmitted by mechanical inoculation as well as by different species of aphids particularly Brevicoryne brassicae and Myzus persicae in semi-persistent manner.
• Besides cabbage and cauliflower, the virus has been reported to infect other Brassica spp. under natural conditions.

Management:

• Control of aphid vectors through the use of insecticides like Metasystox (0.1%) at an appropriate stage is helpful in reducing the spread of the disease.

Other disease of minor importance are:

i. Yellows : Fusarium oxysporum Schlech: Fr f.sp. conglutinans (Wollenw.) Snyder & Han
ii. Wire stem : Rhizoctonia solani Kuhn
iii. Ring spot : Mycosphaerella brassicicola (Fries ex Duby) Lindau
iv. Powdery mildew :Erysiphe polygoni DC.
v. Leaf spots : Cercospora brassicicola Hennings; C. cruciferarum Ellis and Everhart
vi. Soft rot or Curd rot : Erwinia caratovora subsp. carotovora (Jones) Bergey et al.