COTTON LEAF CURL VIRUS DISEASE
(Muhammad Hamza & Muhammad Wajid Javed)
Cotton (Gossypium hirsutum) is an important fiber and cash crop as it contributes a lot to the national economy as it is a source of income for many people. This crop is very important in textile industries. Cotton not only provides fiber to textile industry but its seed is used as an important source of edible oil. Pakistan earns about 60% of the foreign exchange by the export of cotton. Therefore, cotton holds a remarkable position in our economy.
Cotton is affected by many insect pests and diseases but Cotton Leaf Curl Virus (CLCuV) Disease is the most destructive disease of cotton as it causes heavy losses and it is a serious threat to cotton. This disease was first time reported in Nigeria in 1912. In 1959, it was reported in Philippines. In Pakistan, it was first reported in 1967 at Tiba Sultan Pur near Multan district. In its early times it was left un-noticed but in 1993 – 1995 it appeared in epidemic form in Pakistan and caused huge losses.
Cotton Leaf Curl Virus is a single stranded DNA virus. Cotton Leaf Curl Virus is a member of “Begomovirus” and family “Geminiviridae”. This virus is neither seed born nor soil borne. It has some alternate hosts where it survives these alternate hosts are Tomato, Tobacco, Lehli, Dhatura, Okra, China Rose etc. The most important means of virus transmission is whitefly (Bemisia tabaci), some scientists also considered Bemisia argentifoli as insect vector of cotton leaf curl virus. Whitefly has 473 different host plants. This whitefly acquires the virus from infected plant and transmits it to the healthy ones. Ones the virus is acquired by the whitefly it remains in it throughout its life. Cotton leaf curl virus requires 30 minutes of feeding on infected plant to acquire the virus and a latent period of 24 hours and then 30 minutes of feeding on healthy plant to transmit the virus leading to unnoticeable changes at the initial stage to remarkable variations in growth patterns at later stages of cotton plant development.
Symptoms shown by cotton leaf curl virus are the upward or downward curling of leaf. Vein thickening is shown by the leaves which are small veins thickening and main vein thickening. Infected plants become dark green in color. Plants become stunted in growth with no proper yield patterns and the petioles become twisted or deform to spring shape. Enation occurs on the leaf which is a small leaf like structure forms under the leaf mainly due to tissue malformation and sometimes due to blockage of veins and hence hindrance in food and water channels. Enation is the main identification mark of cotton leaf curl virus disease.
Many environmental factors are responsible for the establishment of cotton leaf curl virus. Temperature range of 28 – 40oC, relative humidity of 58 – 60%, wind speed at the rate of 6 – 12 km/h is suitable for the development of cotton leaf curl virus. Similarly, optimum environmental conditions are important for the whitefly (Bemisia tabacii) or (B.argentifoli). These optimum conditions are less rainfall, less humidity and optimum maximum and minimum air temperature. Alternate hosts also provide support in the survival of the virus.
For managing cotton leaf curl virus disease, there are several methods which can be adopted to manage this destructive lethal disease. The use of resistant varieties are an important source for the control of cotton leaf curl virus disease but now the resistance has been broken by a strain of cotton leaf curl virus called “Burewala strain” mainly in prominent attack noted from about in 2005 but still the use of resistant varieties cannot be left to avoid heavy and unbearable losses. Some resistant varieties are NIAB – 884, NIBGE – 2. Field sanitation practices should be properly adopted. Strict quarantine regulations should be imposed in order to check the incoming planting material for any viral or insect infection. There should be no presence of alternate host near the field where cotton is grown. Foliar application of macro nutrients and micro nutrients is very helpful for managing this disease. If an infected plant is seen in the field, uproot that plant immediately and burn that infected plant. Diseased plant debris should also be burned. Control of insect vector by using insecticides like Diafenthiuron, Buperofezan, Imidacloprid. But World Trade Organization recommends the judicious use of pesticides in order to avoid the residual effects which pollute our environment. Biological control is another option as this is environmental friendly. Use of laundry detergent mixed with plant derived oil is suitable for control of whitefly. Similarly, spraying the mixture of plant derived oil in large volume of water also reduces whitefly population which ultimately reduces cotton leaf curl virus disease. Use of furnace oil and mixture of Nimbokil and furnace oil is also found suitable for managing cotton leaf curl virus. Neem extract can also be used.
1. Muhammad Wajid Javed is student of B.Sc. (Hons.) Agriculture (Department of Agri. Entomology, University of Agriculture, Faisalabad). He is also affiliated with Agrihunt as an author.
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2. Muhammad Hamza is student of B.Sc. (Hons.) Agriculture (Department of plant pathology, University of Agriculture, Faisalabad.) he is also affiliated with Agrihunt as an author