1823     Review article An overview of cotton leaf curl virus disease (CLCuD) a serious threat to cotton productivity Amjad Farooq 1 , Jehanzeb Farooq 1 , Abid Mahmood 1 , Amir Shakeel 2 , Abdul Rehman 3 , Asia Batool 4 , Muhammad Riaz 1 , Muhammad Tasdiq Hussain Shahid 1 and Saira Mehboob 4 1 Cotton Research Institute, Ayub Agricultural Research Institute, Jhang Road, Faisalabad, Pakistan 2 Department of Plant Breeding & Genetics, University of Agriculture, Faisalabad, Pakistan 3 Department of Plant Pathology, University of Agriculture, Faisalabad, Pakistan 4 Plant Pathology Section, Plant Protection Research Institute, AARI, Jhang Road, Faisalabad *Corresponding authors: amjad1545@hotmail.com, jehanzeb1763@hotmail.com Abstract Cotton Leaf Curl Disease is among the most devastating natural calamity that inflicted huge losses to cotton crop productivity especially in Pakistan during the last 20 years. The dilemma of CLCuD is still under discussion among the researchers since its appearance in 1967. In 1992-93, CLCuD appeared in epidemic form which caused a decline in yield down to 9.05 million bales and during 1993-94, to 8.04 million bales in Pakistan. For screening against CLCuV to develop virus resistant cultivars disease was induced through grafting, delayed sowing and whitefly mediated transfer. The disease epidemiology is changed by abiotic factors especially temperature and plant age. Cotton leaf curl virus disease not only affect yield but also deteriorate fiber quality traits like Ginning out turn percentage, staple length, fiber uniformity index, fiber fineness, fiber bundle strength, maturity ratio because of change in composition of major fiber components including cellulose, protein, wax and pectin. The uncertainty of inheritance of CLCuD also prevails whether it is under the control of dominant or recessive genes which may be monogenic or polygenic whereas, extrachrmosomal inheritance is also under discussion. The resistance breakdown depends upon the evolutionary potential of the pathogen and the possibility of recombinations, by which new variants of viruses evolved. The resistance gained for Multan-CLCuV became susceptible to Burewala-CLCuV due to virus mutation and lack of durable resistance. Management of CLCuD is the only option that can command the disease in various ways inclusive of change in sowing dates, crop nutrition, cultural practices, vector control, buffer crops and systemic poisoning of cotton seed by seed treatment will make the cotton crop safe in initial 40-50days after sowing. Biotechnology can also aid in controlling this disease through transcriptional gene silencing. By using biotechnological tools broad spectrum resistance can be introduced against all viruses present in the field. Keywords: Cotton, Biotic stresses, whitefly, CLCuD, Geminiviruses, Begomoviruses. Abbreviations: CLCuD= Cotton leaf curl virus disease, ssDNA= Single-stranded deoxyribonucleic acid, CLCuMV= Cotton leaf curl Multan virus, CLCuRV= Cotton leaf curl Rajasthan virus, CLCuAV= Cotton leaf curl Alabad virus, CLCuKV= Cotton leaf curl Kokhran virus, PaLCuV= Papaya leaf curl virus (), CLCuBV= Cotton leaf curl Bangalore virus, CLCuBuV= Cotton leaf curl Burewala virus, CLCuShV=Cotton Leaf Curl ShahdadPur Virus, CLCuMV=Cotton leaf curl Multan Virus, CLCrV= Cotton leaf crumple virus, GOT%= Ginning out turn percentage, ELISA=Enzyme linked immunosorbant assay, PDR= Pathogen disease resisstance, SI=Severity index, PDI= Percent disease incidence, RFLP= Restriction fragment length polymorphism. Introduction The environmental calamities including biotic and abiotic stresses are the major threats to agriculture and food security. Biotic stresses including viruses cause many important plant diseases and are responsible for huge losses in crop production and quality in all parts of the world as well as in Pakistan. A class of Geminiviruses was observed in 1978, on plants with distinct characteristics of size and appearance of geminate particles and was subsequently proven to be evidence that these are single-stranded deoxyribonucleic acid (ssDNA) virus (Mathews, 1987). The family Geminiviridae comprises of three genera i.e. Mastrevirus, Curtovirus and Begomovirus. A notorious group of these viruses belongs to genus Begomovirus, cause of major threat to cotton crop which is well known as Cotton leaf curl virus disease (CLCuD) and is transmitted by whitefly i.e. Bemisia tabaci complex (including B. argentifolii) in a persistent manner (Brown et al., 1995; Rybicki and Fauquet, 1998). Most of the Begomoviruses comprised of two genomic components called DNA-A and DNA-B, which are indispensable for a disease that is transmitted by whitefly Bemisia tabaci (Monga et al., 2011). There are numerous viruses from the Old World which have only a single constituent, analogous to DNA-A, which has been isolated and shown to bring on disease symptoms (Navot et al., 1991; Dry et al., 1993; Tan et al., 1995). The DNA isolated from an infected plant of cotton with CLCuD showed wide-ranging homology with the DNA- A component and other Begomoviruses in the Indian sub- continent (Zhou et al., 1998). Seven diverse species of