Cotton Leaf Curl Disease, an Emerging Whitefly Transmissible Begomovirus Complex

In recent years leaf curl disease of cotton has become a major limiting factor in the production of cotton, which is an important fiber cash crop. In the last two decades or more, leaf curl disease in cotton took on epidemic proportions in Pakistan. In the early 1990’s cotton leaf curl disease (CLCuD) appeared in the bordering parts of India in the states of Rajasthan and Punjab and spread to entire cotton growing areas in Rajasthan, Punjab and Haryana. The very early appearance of the disease devastated entire crops of susceptible varieties. This led to a ban on the cultivation of Barbadense cotton and the collapse of several popular cotton varieties. The characteristic symptoms of CLCuD are general stunting, upward or downward curling of leaves and thickening of veins which turn dark green. Enations of various shapes and sizes numbering up to twelve develop on the thickened veins on the abaxial side of leaves. Fewer, smaller balls are formed which sometimes fail to open. In the field CLCuD is a complex problem that needs an integrated management approach. Six species of the genus Begomovirus, family Geminiviridae viz. Cotton leaf curl Alabad virus (CLCuAV), Cotton leaf curl Gezira virus (CLCuGV), Cotton leaf curl Kokhran virus (CLCuKV), Cotton leaf curl Multan virus (CLCuMV), Cotton leaf curl Rajasthan virus (CLCuRV) and Tomato leaf curl Bangalore virus-Cotton [Fat] associated with DNAand DNA-1 (genus Nanovirus) are reported to induce CLCuD. All these begomoviruses are monopartite DNA-A, transmissible by the whitefly Bemisia tabaci. Begomoviruses are recognized as the most abundant and most severe viral pathogens of cotton, worldwide. Yield losses due to CLCuD amount to 60% or more if the disease appears at a very early stage of the crop. The aim of this review is to discuss and understand our current knowledge of CLCuD complex of cotton, and epidemiology, management and future prospects. _____________________________________________________________________________________________________________