Molecular characterization of begomoviruses and DNA satellites associated with okra leaf curl disease in Cameroon

Begomovirus disease complex: emerging threat to vegetable production systems of West and Central Africa

“…With the advent of more advanced molecular techniques in the study of begomoviruses, such as polymerase chain reaction (PCR), rolling cycle amplification (RCA)/restriction fragment length polymorphism (RFLP), and sequencing, the situation has greatly improved, leading to the identification of previously unknown begomovirus/satellite complexes infecting tomato, okra and pepper such as Tomato leaf curl Cameroon virus (ToLCCMV), Tomato leaf curl Nigeria virus (ToLCNGV), Tomato leaf curl Ghana virus (ToLCGHV), Tomato leaf curl Kumasi virus (ToLCKuV), and Tomato leaf curl Togo virus (ToLCTGV), which could collectively be termed the West African tomato-infecting begomoviruses (WATIBs) (Figure 3). Beside the WATIBs, others such as Tomato yellow leaf curl Mali virus (TYLCMLV), Pepper yellow vein Mali virus (PepYVMLV), and Tomato leaf curl Mali virus (ToLCMLV) have been identified infecting tomato and pepper in the region [49][50][51][52][53][54][55][56][57] (Figure 3 arrows). Apart from the pepper and tomato-infecting begomoviruses, others such as Cotton leaf curl Gezira virus (CLCuGeV), Okra leaf curl Cameroon virus (OLCuCMV), and Okra yellow crinkle virus (OYCrV) have been identified infecting okra in West and Central Africa [49,52,56,58] (Figure 3).…”

“…Beside the WATIBs, others such as Tomato yellow leaf curl Mali virus (TYLCMLV), Pepper yellow vein Mali virus (PepYVMLV), and Tomato leaf curl Mali virus (ToLCMLV) have been identified infecting tomato and pepper in the region [49][50][51][52][53][54][55][56][57] (Figure 3 arrows). Apart from the pepper and tomato-infecting begomoviruses, others such as Cotton leaf curl Gezira virus (CLCuGeV), Okra leaf curl Cameroon virus (OLCuCMV), and Okra yellow crinkle virus (OYCrV) have been identified infecting okra in West and Central Africa [49,52,56,58] (Figure 3). Putative recombination events were detected in begomovirus genomes for all three plant species studied, indicating that recombination is an important mechanism for their evolution.…”

“…The presence of DNA satellites in Africa was first shown in a survey for alphasatellites in samples from Asia and Africa, where they were found in different plants from both Egypt and Kenya [29] (Figure 4). Recently, one betasatellite, Cotton leaf curl Gezira betasatellite (CLCuGB), initially identified in the Nile basin, has been identified in West and Central Africa, associated with diseased okra and tomato [52,55,56,58,64] (Figure 5). Two new betasatellites, Ageratum leaf curl Cameroon betasatellite (ALCCMB) and Tomato leaf curl Togo betasatellite (ToLCTGB), have been identified infecting A.…”

“…Also, new types of alphasatellites, Ageratum leaf curl Cameroon alphasatellite (ALCCMA), Tomato leaf curl Cameroon alphasatellite (ToLCCMA), Okra leaf curl Mali alphasatellite (OLCuMLA), Okra leaf curl Burkina Faso alphasatellite (OLCuBFA), and Okra yellow crinkle alphasatellite (OYCrA), have been identified infecting A. conyzoides, okra, and tomato [50][51][52][53]56,58] in West Africa and the lone Central African state, Cameroon.…”

“…These differences and similarities can have important bearings on the epidemiology of begomovirus-incited diseases of vegetable, fruit, and fiber crops [96,99], and in some instances are known to drive begomoviral diversification [100]. The size of a whitefly vector population is often directly associated with begomovirus disease incidence, including a number of outbreaks [44,47,50,52,54,56,64,101,102] and epidemics in Africa such as the CMD pandemic in East and Central Africa [103]. However, in some instances, extremely high incidence has been observed even when population levels are low.…”