Epidemiology of groundnut rosette virus disease: current status and future research needs@

Abstract

Rosette is the most destructive virus disease of groundnut in sub-Saharan Africa. It is caused by a complex of three agents, namely groundnut rosette assistor virus, groundnut rosette virus and its satellite RNA. The disease appears to be indigenous to Africa as it has not been recorded elsewhere. Thus rosette represents a newencounter situation as the disease is thought to have spread to the introduced groundnut from indigenous host plants. Rosette has been known since 1907 and much information has been obtained on the main features of the disease, viz. its biology, transmission, viral aetiology and diagnosis, and the impact of chemical control of the aphid vector, cultural practices and virus-resistant varieties on disease management. However, there are still many gaps in the available knowledge, especially the reasons for the large and unpredictable fluctuations in the incidence and severity of rosette disease throughout sub-Saharan Africa. Three unresolved issues of particular importance concern the nature of the primary source(s) of inoculum, the means of survival of virus and vector during unfavourable periods, and the distances over which the aphid vector can disperse and disseminate virus. Now that the aetiology of the disease is understood and diagnostic tools have been developed, the time is opportune for new initiatives in understanding the ecology and epidemiology of rosette. Substantial progress can be made by developing a co-ordinated multi-disciplinary research programme and making full use of the latest techniques, approaches and experience gained elsewhere with other insect-borne viruses. This information would help to explain the sporadic disease epidemics that cause serious crop losses and sometimes total crop failure, and would also facilitate the development of disease forecasting methods and sustainable integrated disease management strategies. Davies J C. 1972. Studies on the ecology of Aphis criicci\ww Koch (Hem., Aphididae). the vector of rosette disease of groundnuts. in Uganda. Birllrtiii of Eritoriinlagii.tr1 ReseciriA 62: 169-1 8 1. Davies J C. 197%. Insecticides for the control of the spread of groundnut rosette disease in Uganda. PANS 21: 1-7. Davies J C. 197%. Use of Menazon insecticide for control of rosette disease of groundnuts in Uganda. Tropical Agric~tltitre. Triiiiil~iil 52:359-367. Davies J C. 1976. The incidence of rosette disease in groundnut in relation to plant density and its effects on yield. Anrials of Applied Biology 82:489-501. Davies J C, Kasule F K. 1964. The control of groundnut rosette disease in Uganda. Tropicril Agriculticre. Trinidrd 41 303-309. de Berchoux C. 1960. La rosette de I'arachide en Haute-Volta. Comportenient des lignees resistantes OlPagirieux 15229-233. Demler S A, Rucker D G, de Zoeten G A, Ziegler A, Robinson D J, Murant A F. 1996. The satellite RNAs associated with the groundnut rosette disease complex and pea enation mosaic virus: sequence similarities and ability of each other's helper virus to support their replication. Jourriiil of' Gerie...

Molecular biology of umbraviruses: phantom warriors

“…Umbraviruses, and in particular their taxonomy, classification and evolution, and their biological properties, such as host range, pathology, geographical distribution, mechanisms of aphid transmission, interaction with assistor luteoviruses and satellite RNAs, have been reviewed in detail (Murant, 1993;Demler et al, 1996b;Naidu et al, 1998;Robinson & Murant, 1999;Taliansky et al, 2000). In this article we will focus on new molecular findings that highlight the distinctive features of umbraviruses that follow from the absence of a capsid protein and virions.…”

“…The most economically important umbravirus is GRV, which is endemic throughout sub-Saharan Africa. Sporadic, unpredictable outbreaks of groundnut rosette disease (actually caused by a satellite RNA of GRV) cause severe crop losses (Naidu et al, 1998). For example, an epidemic in the Eastern Province of Zambia in 1995 affected about 43 000 ha and caused losses approaching US$ 5 million.…”

“…One or both of the carrot-infecting umbraviruses probably occurs worldwide wherever carrots are grown, but they are uncommon in commercial crops because the insecticides used to control carrot fly also control the aphid vectors of CMoV and CMoMV. However, because of their peculiar properties and the attendant difficulties in working with them, the molecular virology of umbraviruses has been developed only in the last decade, when nucleotide sequencing has revealed unique 'umbravirus' features (Demler et al, 1993;Taliansky et al, 1996;Gibbs et al, 1996).Umbraviruses, and in particular their taxonomy, classification and evolution, and their biological properties, such as host range, pathology, geographical distribution, mechanisms of aphid transmission, interaction with assistor luteoviruses and satellite RNAs, have been reviewed in detail (Murant, 1993;Demler et al, 1996b;Naidu et al, 1998;Robinson & Murant, 1999;Taliansky et al, 2000). In this article we will focus on new molecular findings that highlight the distinctive features of umbraviruses that follow from the absence of a capsid protein and virions.…”

Groundnut Rossette: A Virus Disease Affecting Groundnut Production in Sub-Saharan Africa

“…Hence, the dynamics of the groundnut rosette disease pathosystem are influenced by many biotic and environmental factors. The most critical information lacking about groundnut rosette disease epidemiology involves the off-season survival of the disease agents and aphid vector, and their spread during the cropping season into and between groundnut crops (49). These gaps must be filled in to develop efficient technologies for groundnut rosette disease management.…”

“…Studies were initiated at several locations across SSA to better understand the epidemiology of the disease, but the lack of etiological knowledge and diagnostic tools precluded rapid advances. Therefore, several of the important aspects of rosette disease, such as the underlying causes of groundnut rosette disease epidemics, are unresolved (49).…”