COTTON LEAF CURL VIRUS DISEASE

                                

             

  Cotton leaf curl disease of cotton is caused by the Cotton leaf curl geminivirus (CLCuV). Leaves of infected cotton curl upward and bear leaf-like enations on the underside along with vein thickening. Plants infected early in the season are stunted and yield is reduced drastically. This disease is transmitted by an insect vector (white fly). So the possible control measures included control the insect vector, elimination of means of seasonal carryover such as alternate host and etc.

                Cotton, an important commercial crop, is extensively cultivated in Pakistan. It is infected by several pests and pathogens inducing different diseases. Among them cotton leaf curl virus is the most important, causing enormous losses to the crop (Khan and Ahmad, 2005). The disease was first reported by farquharson in 1912 from Nigeria on Gossypium barbadense. In 1924 it was reported in Sudan. Jones arid Mason (1926) recorded it from Tanzania for the first time in I926. Leaf curl virus disease of cotton was first observed at Tiba Sultan near Multan in the year 1967. This disease caused heavy damage to cotton crop during 90’s. In 1991 the cotton area affected by this disease was about 35,000 hectares (Mehbub, et al 1992).In 1993-94 the cotton crop over 889000 hectares was damaged while there was record loss of yield of 1.88 million bales. This disease spread in Sindh in1997, in NWFP in1998 and in Balochistan in 2001.This disease is caused by a white fly transmitted begomovirus (cotton leaf curl virus) (Mansoor, et al 1993, Briddon and Markham, 2000).

 This disease is characterized by either upward or downward curling of leaves. The veins of the leaves become thickened which are more pronounced on the underside. In extreme but not infrequent cases, formation of cup shaped leaf laminar outgrowth called enation appears on the underside of the leaf. Inter nodal distance is reduced and affected plants become stunted. There is reduction in the boll number and boll weight resulting in loss of yield. There is also a negative effect on fiber length, fineness, strength and maturity etc. The white fly is the vector of this disease. The Government and all research Institute/Stations through their all-out efforts tried to control this disease. The genetic stock available at CCRI Multan was carefully screened and it was found that three exotic cultivars viz., CP-15/2, LRA 5166 and CEDEX showed complete resistance to this disease. As a result of crossing between these three exotic cultivars and local varieties, virus resistant varieties viz., CIM-1100, CIM-448, CIM-443, CIM-446, CIM-482 and CIM-473 were developed and were approved by the Punjab Seed Council for general cultivation in the Punjab. These varieties covered about 80% area in the Punjab and yield loss decreased gradually from 2.1 to 0.082 million bales from 1996 to 2001 respectively. (Tariq et. al. 1992)

 However due to new strain of virus commonly known as Burewala strain of cotton virus (BSCV) started damaging the cotton crop in district Vehari in general and in Burewala area in particular during 2001. All the cotton leaf curl resistant commercial varieties as well CP-15/2, LRA-5166 and CEDEX showed susceptibility to BSCV. 3338 genotypes of Gossypium germplasm from CCRI Multan, CRS Multan, CRI Faisalabad,. NIBGE Faisalabad, CCRI Sakrand and CRS Tandojam, planted at Cotton Research Station Vehari, were screened but none of these genotypes was found resistant to Burewala cotton leaf curl virus. The symptoms and alternate hosts of BSCV are similar to those of previous cotton leaf curl virus. After emergence of this new strain of virus the yield loss started increasing. The hot spots of this disease increased from 2.4% to 73.4% during the year 2001-2007. Similarly the area affected under this disease also increased from 4.45% to 70.26% during this period. At present no single variety is resistant to BSCV. This is alarming that the hot spots as well as area affected by this disease are increasing every year and the situation is becoming verse. The cotton is the backbone of agricultural economy of Pakistan, which is being affected due to insurgence of BSCV and there is decease in production.