Abstract
In this review, the genetic diversity of the three causal agents of Groundnut Rosette Disease (GRD) in Sub-Saharan Africa (SSA) are discussed. Epidemics of GRD viruses in SSA, often reduce groundnut productivity. The etiology of GRD is a complex, involving three agents; Groundnut rosette assistor <i>luteovirus</i> (GRAV), Groundnut rosette <i>umbravirus</i> (GRV) and a Satellite-RNA (Sat-RNA) of GRV. The complex etiology and lack of sensitive and specific diagnostic tools, are major limitations in understanding the epidemiology of GRD viruses, and developing appropriate management strategies for the disease. Nucleotide identity of 97 to 100% among GRAV isolates from different regions in Kenya have been reported. Sat-RNA sequences from Kenya shared nucleotide identity of 95% with Malawian isolate (M24S) and 89% with Nigerian isolate (NG3a). GRAV CP gene was highly conserved (97-99%) regardless of the geographical distance. However, for GRV and Sat-RNA diversity increased with increase in geographical distance. In addition, phylogenetic analysis showed that isolates of GRV (ORF3 and 4) and Sat-RNA clustered together depending on the country of origin. Recent study has unveiled a chlorotic variant of Sat-RNA in Kenya with 97% sequence identity to the Malawian chlorotic isolate (M24S). Pathogen derived resistance (PDR) suitable for each diverse regions where the disease occurs is a promising management strategy which mainly depends in studies to deeply understand the genetic diversity of the three GRD causal agents. Currently, GRAV-CP is the best candidate for PDR.
Highlights
Groundnut rosette disease (GRD) was first reported in 1907 from Tanganyika, called Tanzania [1]
GRD has been reported in several other Sub-Saharan African Countries, which include: Angola, Burkina Faso, Cote d’lvoire, Gambia, Ghana, Kenya, Madagascar, Malawi, Niger, Nigeria, Senegal, South Africa, Swaziland, Uganda and the Democratic Republic of Congo (DRC) [2,3,4]
Green and mosaic rosette symptoms caused by synergism among groundnut rosette assistor luteovirus (GRAV), groundnut rosette umbravirus (GRV) and its satellite
Summary
Groundnut rosette disease (GRD) was first reported in 1907 from Tanganyika, called Tanzania [1]. Symptoms similar to GRD, have been reported in some countries of Asia and South America, but diagnostic tests, to confirm the presence of the disease, have not been conducted [5] This disease is considered to be endemic to groundnut growing countries of SSA, and its offshore islands of Madagascar. Recent observations made in groundnut farms in western Kenya have shown that GRD is very severe and highly variable in symptoms diversity causing upto 100% yield losses [10]. The cause of this could lie in the genetic variability of GRD causal agents, the Sat-RNA of GRV [11]. Reports of groundnut crop damage by GRD, underscores the need for further epidemiological studies, and appropriate control/management strategies that reduces the inoculum sources for viral diseases, to prevent resistant/tolerant varieties from succumbing to GRD at high inoculum pressure [12]
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