Cotton leaf curl virus disease

Importance of cotton

Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus Gossypium in the mallow family Malvaceae. The fiber is almost pure cellulose. Under natural conditions, the cotton bolls will increase the dispersal of the seeds.

The plant is a shrub native to tropical and subtropical regions around the world, including the Americas, Africa, Egypt and India. The greatest diversity of wild cotton species is found in Mexico, followed by Australia and Africa. Cotton was independently domesticated in the

Old and New Worlds.

The fiber is most often spun into yarn or thread and used to make a soft, breathable textile. The use of cotton for fabric is known to date to prehistoric times; fragments of cotton fabric dated to the fifth millennium BC have been found in the Indus Valley Civilization. Although cultivated since antiquity, it was the invention of the cotton gin that lowered the cost of production that led to its widespread use, and it is the most widely used natural fiber cloth in clothing today.

Current estimates for world production are about 25 million tonnes or 110 million bales annually, accounting for 2.5% of the world's arable land. China is the world's largest producer of cotton, but most of this is used domestically. The United States has been the largest exporter for many years. In the United States, cotton is usually measured in bales, which measure approximately 0.48 cubic meters (17 cubic feet) and weigh 226.8 kilograms (500 pounds.

Cotton leaf curl virus disease:

Cotton is one of the most important crops of Pakistan, accounting for over 60% of foreign exchange earnings. The present epidemic of cotton leaf curl disease (CLCuD) originated in the Punjab region near the city of Multan and was first reported in 1985, although it was noted in this region as early as 1967. By the early 1990s, CLCuD had become the major limitation to cotton production in Pakistan and it has now spread into India and, more recently, south and west into other provinces of Pakistan. The very characteristic symptoms include leaf curling, darkened veins, vein swelling and enations that frequently develop into cup-shaped, leaf-like structures on the undersides of leaves. Identification of the vector of CLCuD as the whitefly Bemisia tabaci (Genn.) quickly led to the suggestion that the causative agent of the disease is a geminivirus. Researchers soon confirmed the presence of such a virus that is currently ascribed to the genus Begomovirus of the family Geminiviridae, However, in 1999, the aetiology of the disease was shown to be more complex than was originally assumed. Despite the identification of both a begomovirus and a so-called nanovirus-like component, the precise casual agents remain uncertain.

Scientific classification:

Phylum:

              incertae sedis

Class:

             incertae sedis

Order:

             incertae sedis

Family:

             Geminiviridae

Symptoms

Begomovirusll Begomovirus species causing cotton leaf curl disease have geminate particles, approximately 18-20 nm in diameter and 30 nm long and a circular, single-stranded DNA genome. All except Cotton leaf crumple virus have a monopartite genome, with all viral products required for replication, systemic movement and whitefly transmission encoded on a single DNA component of c. 2.75 kB (DNA A). The genome of CLCrV is bipartite. Two smaller, circular, single-stranded DNA molecules, named DNA 1 and DNA β, are associated with a range of monopartite begomoviruses from the Old World including the cotton leaf curl viruses.

These molecules are regarded as satellite molecules as they depend on the helper begomovirus to support one or more stages of their infection cycle (movement and insect transmission for both molecules and, additionally, replication in the case of DNA β). DNA β is symptom-modulating and typical cotton leaf curl disease symptoms only develop when this molecule is present: in the absence of DNA β, the concentration of viral DNA (DNA A) is low and the symptoms of infection very mild. DNA β has a single open reading frame (βC1 ORF), which encodes a suppressor of RNA silencing. DNA 1 is homologous to the DNA-R component of the nanoviruses and encodes a master replication initiator (M-Rep) protein but its presence does not alter symptom expression.                                                                       

Prevention and control:

1.       I.                  Use resistant or tolerant cultivars.
2.    II.            Protect seedlings from whiteflies.
3. III.            Use only good seeds and healthy transplants.
4. IV.            Control whiteflies.
5.   V.            Immediately remove infected-looking plants and bury them.
6. VI.            Control weeds.
7. VII.            Do not plant cotton near tomato and/or other crops susceptible to whiteflies or vice.
8. VIII.            Use acephate-imidacloprid at 50% - 1.8% respectively, at every seven days.
9. IX.            Plow-under all plant debris after harvest or burn them when possible.
10.   X.            Practice crop rotation by planting crops that are not susceptible to whitefly.