Diseases of Vegetable, Ornamental and Spice Crops

Viral Diseases

8. Mosaic
Symptoms:

• Different types of mosaic pattern are produced depending upon the type of virus or virus (s) involved.
• Potato virus Y and its strains generally induce vein and stem necrosis.
• Pepper veinal mottle virus causes mosaic, mottling, distortion and filiform of the leaves leading to bushy appearance of the infected plants (Plate- 8).
• Cucumber mosaic virus produces mosaic, mottling symptoms, reduction in leaf lamina and filiformy.

Pathogen:

• Different viruses like Potato virus Y (PVY) and its strains, cucumber mosaic virus (CMV), tobacco mosaic Virus (TMV), tobacco etch virus, pepper vein banding virus, pepper mottle virus and pepper sever mosaic virus besides chilli mosaic virus are involved in producing mosaic symptoms in this crop.
• PVY virions are filamentous flexuous rods, non-enveloped and consist of single stranded RNA.
• CMV virions are isometric, non enveloped, 29 nm in dia. having single stranded RNA.
• TMV virions are rod shaped non-enveloped having ss RNA.
• Pepper mottle virus is filamentous flexuous having ss RNA.
• Pepper severe mosaic virus is also filamentous flexuous of 761 x 13 nm size consisting of ss RNA.

Disease cycle and epidemiology:

• All associated virus (s) are sap transmissible.
• Except TMV, others are aphid transmissible.
• Predominant aphid vectors are- Myzus persicae, Aphis gossypii and A. craccivora which transmit the virus (s) in non-persistent manner.
• The abundance activity of vectors and the prevailing environmental conditions affect the virus multiplication and spread.

9. Leaf curl

• It is an important disease of this crop and cause significant yield reductions if the vector is present in the area.

Symptoms:

• The symptom of the disease appears as curling of the leaves followed by reduction in their size which later turn pale yellow in colour (Plate-9).
• The older leaves become leathery and brittle.
• The affected plants become stunted.
• Fruits formation in susceptible cultivars is rudimentary and distorted.

Pathogen:

• The disease is caused by tobacco leaf curl virus (TLCV), which belongs to Bigeminivirus group.
• The virus consists of geminate isometric particles measuring 18 to 20 nm in diameter.
• Disease cycle and epidemiology:
• The virus survives from one season to another on various annual and perennial hosts and transmitted to pepper by the vector white fly named Bemisia tabaci.
• The epidemic of the disease depends on the availability of the vector, sources of inoculum, vector activity and their population and prevailing environmental conditions.
• During wet weather, the spread of the disease becomes slow due to reduced activity of vector.

Management:

• Pepper varieties like Punjab Lal, Perennial and Guhati Black are resistant to mosaic viruses belonging to Poty and Cucumovirus groups.
• Planting of maize as barrier crop is also helpful in reducing the mosaic incidence.
• Combined use of yellow traps and insecticidal sprays reduces the population of vectors.

Minor disease of importance are:

1. Stem rot (Sclerotium rolfsii Sacc.),
2. Grey mould (Botrytis cinerea Pers. ex Fr.),
3. Choenophora blight or bud rot (Choenophora cucurbitarum (Berk. & Rav.) Thaxter),
4. Fusarium wilt (Fusarium oxysporum Schlecht. ex Fr. f. sp. capsici)
5. Soft rot (Erwinia caratovora sub. sp. carotovora (Jones) Bergey et al.).