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

Viral Diseases

4. Yellow vein mosaic (YVM)
Symptoms:

• The characteristic symptoms include vein yellowing and thickening of leaves forming a net work of veins and veinlets in the infected leaves (Plate-4).
• Initially the leaves exhibit only yellow coloured veins but under severe infection, the leaves become completely chlorotic and turn yellow.
• The chlorophyll content of the leaves is reduced. Infected plants produce very few small sized leaves, deformed and give a stunted look.
• Affected plants produce very few small sized pale fruits.

Virus

• The disease is caused by Yellow Vein Mosaic Virus (YVMV) and belongs to the Bigeminivirus.
• The size of virus is 18 x 30 nm.
• Virus particles are spherical, isometric measuring 28-30 nm.

Transmission

• Virus is not sap transmissible but under artificial conditions, it can be transmitted by grafting.
• In nature, virus is transmitted by white fly Bemisia tabaci.
• Disease cycle and epidemiology:
• The virus is not sap transmissible but under artificial conditions it can be transmitted by grafting. In nature, the virus is transmitted by insect vector, white fly (Bemisia tabaci Genn.) in a persistent manner.
• Both wild and cultivated plants serve as the source of inoculum and the incidence of the disease in a particular area depends upon the prevalence of wild or cultivated host plants, population buildup of the vectors and environmental conditions.
• Dry hot weather with little or no rainfall was conducive for disease development and also for the multiplication of the vector population

Management:

• Various cultural practices like destruction of wild hosts from in and around the field, avoidance of mixed cropping of pumpkin , adjustment of date of sowing to avoid the period of maximum population of the whiteflies and regular removal of affected plants upto 55 days help in reducing the incidence of the disease.
• Application of yellow coloured polythene mulch significantly delays the appearance of the disease.
• Use resistant cultivars like Punjab Padmini, Punjab-8, Prabhani Kranti and Hissar Unnat.
• Four sprays of Metasystox (demeton-S-methyl) at 15, 30, 45 and 60 days after sowing have been reported effective in controlling the insect vectors and keeping the disease under check.