Towards Sustainability of Groundnut and Cereal Production in West Africa: Management of Peanut Clump Virus

Peanut clump disease is known to cause losses exceeding 40 million US dollars to groundnut ( Arachis hypogaea ) alone on a global scale. In Africa, it is caused by peanut clump virus (PCV) and is distinct from the Indian peanut clump virus (IPCV) that occurs in the Indian subcontinent. Infected plants are severely stunted, often showed chlorotic lesions on younger leaves and older leaves are dark green in colour. The virus has also been shown to infect a range of monocotyledonous plants, which include wheat, barley, maize, sorghum, pearl millet and various grassy weeds. In addition to groundnut, the virus has the potential to cause crop losses at least in sugarcane, wheat, barley, maize, sorghum, chillies and bambara groundnut. PCV also infects such important crops as cowpea (niebe) and forage legumes (eg. Stylosanthes spp.), but crop losses in these hosts are yet to be assessed. PCV is soil born and is vectored by the persistent, soil-inhabiting root parasite, Polymyxa graminis . This parasite survives for many years in the soil in the form of highly resistant resting spores. PCV is seed-transmitted in groundnut and suspected to be transmitting through seed of a range of monocotyledonous and dicotyledonous hosts. Evidence has been obtained to show that IPCV can establish in disease free areas if virus-containing seed from monocots is planted in soils containing Polymyxa species. Therefore to prevent further spread of PCV in West Africa extreme caution is essential in selecting the seed. Cultural practices such as trap cropping with pearl millet, and judicious time of sowing, have been shown to reduce significantly clump disease incidence in India. Cropping systems that avoid cereals, excellent hosts for multiplication of virus inoculum in the soil, before growing groundnut are also favorable to reduce the disease incidence. Since no resistance to PCV has been identified in cultivated groundnut, the wild Arachis germplasm is currently evaluated for resistance to the virus. Disease management by cultural practices is the most feasible currently available method.

In picture : Philippe Delfosse, Virologist at ICRISAT-Sadoré, Niger, having a close look at groundnut plants infected with the peanut clump virus in Senegal. Healthy plants are easily identified in the background of the picture.

Although existence of diversity among various isolates of PCV has been reported, no attempts have been made to determine the distribution and biological characteristics of different isolates. For example, rice stripe necrosis virus (RSNV) is also transmitted by Polymyxa sp. and occurs in Côte d'Ivoire, Nigeria, Liberia and Sierra Leone. It is a virus very similar to PCV but it was not fully described; its serological and genomic properties need to be clarified and it is possible that RSNV is a member of the Pecluvirus , the genus to which PCV and IPCV belong. This information is vital for the diagnosis of these viruses and for implementing the management practices. Additionally very little is known about the diversity among isolates of Polymyxa spp. in West Africa. The Polymyxa sp. transmitting RSNV infects rice roots whereas this crop is not a host for Polymyxa sp. transmitting IPCV. Pearl millet was reported not to be a host for Polymyxa sp. in Senegal but recent experiments proved the contrary. The studies on the host range of both Polymyxa and the viruses it transmits are crucial before developing strategies for the management of this group of viruses in West Africa.

A collaborative project, funded by the Directorate General for International Cooperation (DGIC - Belgium) was initiated in 2000 between the Unité de Phytopathologie, Université catholique de Louvain, Louvain-la-Neuve, Belgium and ICRISAT to study and better understand the complex epidemiology of the peanut clump disease in West Africa and to develop simple cultural practices for the control of the disease based on the information generated during this project and on the research conducted in the past in India on IPCV.

For more information please contact:

Dr Delfosse P
Special Project Scientist (Virology),
ICRISAT-Sadore,
Niger.