Cotton

The Role of Satellites in the Evolution of Begomoviruses

“…Before the emergence of monopartite begomoviruses at the end of the last century, only bipartite begomoviruses were endemic in various parts of the world, except Africa, where leaf curl diseases have affected cotton for a long time. It is expected that some endemic monopartite begomovirus may have moved to newly introduced varieties of cotton to promote the cotton industry in Africa [ 9 ]. Interestingly, CLCuD did not occur in India until 1989, when it was first observed in a few plants of an introduced susceptible genotype, and soon the disease became a menace [ 1 ].…”

“…Cassava mosaic, cotton leaf curl, bean golden mosaic, cowpea golden mosaic, and yellow mosaic of legumes were the most serious whitefly-transmitted diseases (WTDs). Cassava mosaic and cotton leaf curl diseases are classical examples of the emergence of diseases by the introduction of new crops or genotypes susceptible to indigenous viruses occurring in new regions [ 2 , 9 ]. Cassava was introduced to Africa from South America in 1558, and the mosaic disease of cassava (CMD) was first recorded in East Africa in 1894; since then, CMD has spread to all cassava-growing areas in Africa [ 10 ].…”

“…Cassava was also introduced to India, where CMD became a major threat to the cultivation of cassava in the 1940s [ 1 ]. Cotton leaf curl disease (CLCuD), perhaps the most destructive WTD as almost no yield is obtained from the affected plants, was first observed in Nigeria in 1912 in cotton varieties introduced from America to improve cotton production in Africa [ 9 ]. However, CLCuD remained confined to Nigeria and Sudan [ 8 ].…”

“…The betasatellites associated with CLCuD are not specific; for example, the association of the cotton leaf curl Multan betasatellite has been detected in association with eight different CLCuD-causing begomoviruses [ 9 ], and eight distinct betasatellites have been detected to be associated with tomato leaf curl disease [ 18 ], indicating that CLCuD complexes are still evolving. Both AYVV and cotton leaf curl Multan virus (CLCuMV) are also associated with other circular ssDNA molecules, now referred to as alphasatellites, which are about half the size of begomovirus genomes and, unlike betasatellites, are capable of self-replication in host plants but require a helper begomovirus for movement in plants as well as insect transmission [ 12 , 19 ].…”