Identification of DNA components required for induction of cotton leaf curl disease

Cotton leaf curl disease (CLCuD) is a major constraint to cotton production in Pakistan. Infectious clones of the monopartite begomovirus cotton leaf curl virus (CLCuV), associated with diseased cotton, are unable to induce t ypical symptoms in host plants. We have identified and isolated a single-st randed DNA molecule approximately 1350 nucleotides in length which, when co inoculated with the begomovirus to cotton, induces symptoms typical of CLCu D, including vein swelling, vein darkening, leaf curling, and enations. Thi s molecule (termed DNA beta) requires the begomovirus for replication and e ncapsidation. The CLCuV/DNA 1/DNA beta complex, together with a similar com plex previously identified in Ageratum conyzoides, represent members of an entirely new type of infectious, disease-causing agents. The implications o f this finding to our understanding of the evolution of new disease-causing agents are discussed. (C) 2001 Academic Press.