COTTON LEAF CURL VIRUS
CLCV found to be most important disease, considered as most severe and destructive
By M. MITHAL JISKANI,
Assistant Professor (Plant Pathology),
Sindh Agriculture University, Tandojam
Aug 02 - 08, 2004
Cotton is called the back-bone of Pakistan's economy. It is one of the most important fibre and cash crop, which accounts major contribution in foreign exchange earnings for the country, through the export of raw cotton and cotton products. It also provides raw material to local domestic cotton industry. About 40% labour force of the country is employed in cotton fields and cotton processing mills. It has 85% share in the total vegetable oil produced in the country, on the other hand, an important by-product 'cotton seed cake', is valuable source of protein for ruminant cattle.
Cotton production practices adopted by farmers play an important role for increased per acre yield. The crop has maximum area in Punjab followed by Sindh and very negligible in NWFP. The yield per hectare of seed cotton in Punjab is more to that of Sindh province. The area, production and yield have been showing an increasing trend since 1947. The increase in production is due to increase in yield per acre rather than increase in area. However, during some years, the production and yield have shown considerable fluctuation, the causes may be many more, but a disease 'cotton leaf curl' could not be ignored, neglected and or regretted, because it also cause variable loss time by time to the crop.
The crop record revealed that cotton leaf curl virus (CLCV) found to be most important disease, considered as most severe and destructive. This disease causing virus was first time recorded in Nigeria (1912), Sudan (1924), Tanzania (1926), Philippine (1959). In Pakistan, it was first time recorded in 1967 at Multan (Punjab) on some cotton plants. It was a miner disease until 1987, but in 1991-92, it becomes severe and since 1992-93 causing a huge production and monetary loss to the nation. In Sindh, this disease was first reported during 1996 at Ubauro, district Ghotki, and is reached up to New Saedabad, district Hyderabad, during 1999-2000. It is quite difficult to present accurate estimates of the losses due to cotton leaf curl disease, because the losses vary from year to year and from one area to the other. Sometimes the cotton fields have been found to show as much as 100 percent damage. It is becoming obvious that now, it is up to the cotton growers and crop protectionists, to design and formulate ways or mean to combat all enemies of the crop, so that the losses may be minimised.
The cause, symptoms, preventive and curative control measures of cotton leaf curl virus disease, are being summarised here under, for the benefit of the cotton growers, as a reminder for researchers so that they could plan their future strategies and for extension workers so that they may to be alert.
PATHOGEN: The disease is caused due to cotton leaf curl bigeminivirus (CLCV), belongs to Gemini group, sometimes refer as Gossypium virus 1.
HOST RANGE: More than 60 different crop, weed and ornamental plants are reported as host of disease causing virus.
SERIOUSNESS: Cotton, lady's finger, tomato, chilli, cucurbits (especially water melon), beans, sunflower, sesame, soybean, cow peas, egg plant (brinjal), sun kukra, china rose, thorn apple (dhatura), mint (podina), holly hock (gul-e-khera), Zinnia, AK (Calotropis), shesham (talhi) and citrus species are sometimes found seriously affected by the disease.
TRANSMISSION: The disease transmitted by feeding of the white fly, Bemisia tabaci (Fig 1) with in 6.5 hours. A single female, carrying virus, can infest many plants. It may also be kept in mind that white fly is known to survive on as many as 53 host plant species, and is responsible for transmitting 23 crop diseases in region. At global level, white fly infests 600 different plant species.
PERPETUATION: The disease causing virus survives in several different plant hosts, from which it may spread.
SYMPTOMS: Upward and downward curling of leaves accompanied by small and main vein thickenings (SVT & MVT) on leaves, pronounced on underside (Fig 2). If a diseased leaf is viewed from beneath against the light, thickened vein found darker green and opaque than normal. In extreme but not in frequent cases, formation of cup shaped or leaf laminar (veins) outgrowth called "enation" appears on the back or underside of the leaf (Fig 3). The newly produced leaves are small, excessively crinkled and curled at the edge. Primary stem often tends to grow taller than normal. The internodes being elongated and irregularly curved but sometimes the whole plant is stunted. The flowers checked in growth and become abortive. The bolls remained small in size and failed to open. All parts of badly hit plants are very brittle and ready broken.
MANAGEMENT: Use of proper cotton production technology is economical and most effective for management of all diseases (including this). Therefore, following disease management practices may help to save the crop from CLCV as well as other major and minor diseases of cotton.
*Cultivation of disease resistant variety is only safe measure.
*Lady's finger (okra), sun kukra, china rose, thorn apple (dhatura), mint (podina), karund, cucurbits (especially water melon), beans, tomatoes, tobacco, chillies, soy bean, sun flower, cow peas, egg plant (brinjal), holly hock (gul-e-khera), zinnia, sesame, Ak (Calotropis), shesham, citrus species etc. are recorded as alternate host plants of cotton leaf curl virus as well as white fly, and also some of them are alternate host of boll worms. Therefore, they all must be eradicated before, during and after cotton cropping season. Cotton growing zones may play a better role for this purpose.
*The disease (CLCV) is not seed transmitted but use of healthy seed, acid delinting and chemical seed treatment is recommended as preventive measure. The seed treatment with suitable insecticides helps to reduce the whitefly (vector of virus) population in the beginning and also help the plant to gain vigour for averting the damage by virus.
*Eradication including collection and burning of plant debris may help to control disease, because disease inoculum (the virus) may also survive through plant debris. Therefore, the cotton stubs should be removed from the field just after last picking, because sprouts from diseased plant stubs provide inoculum for transmission of the disease.
*Deep ploughing with short duration, at least two months before sowing, help to control weeds, which other wise will serve as alternate host of virus.
*Crop rotation with non-host crops is useful.
*Mixed cropping with alternate host crops of the virus (for example Lady's finger (okra or bhindi) and sesame or tir/til), specially, inter cropping of cotton in orchards may be avoided.
*Proper use of irrigation and chemical fertilisers improves the disease resistant power in cotton plants.
*The healthy, vigorous plants of cotton should preferably be kept at the time of thinning.
*As the whitefly play a role to transmit the cotton leaf curl virus from diseased plant to healthy one, hence whitefly must be controlled through various possible methods, including cultural practices and using proper insecticides. The whitefly found most active before sun rise, therefore the spraying should be done at least one hour before sun rise.
Meanwhile, use of proper cotton production technology as per recommendations of agricultural experts or researchers is economical and most effective for cotton disease management. It is out look and responsibility of the cotton growers to adopt the modern cotton production technology and play a role for the development and prosperity of the country.