Rice is the staple food and leading source of calorific intake for more than half of the world’s population. In West Africa rice is an increasingly important crop with raising consumption. However, average yield of 1.7 t ha –1 in the region is lowest in the world due to a number of bio-physical constraints. Blast caused by Pyricularia grisea (teleomorph: Magnaporthe grisea), occurs in all rice-growing ecologies and is a major constraint in upland environments where predisposition factors could favour disease development to epidemic proportions. In West Africa yield losses of 3.3 – 77 % have been reported, depending on the agro-ecological conditions. Globally, rice blast is primarily controlled by using resistant cultivars and/or application of fungicides, although problems are associated with both forms of management. Where blast is prevalent, resistant cultivars have an expected field life of only 2-3 growing seasons due to the high diversity of the virulent forms of the pathogen. With fungicides, pathogen resistance, economic as well as social costs to the farmers are issues of concern. Biotechnological approaches are being explored to identify pathogen-specific targets for developing environmentally compatible fungicides. We have generated baseline data on the genetic and pathotypic diversity of the rice blast pathogen populations in four West African countries Cote d Ivoire, Burkina Faso, Ghana and Nigeria. Key rice screening sites have been characterised and the dominant lineage/pathotype groups identified. This data is being used as a framework to identify resistance sources. Farmer participatory evaluation of these resistant material and utilisation of partial and major gene resistances is critical to the development and deployment of durable blast resistance in the West African region. Integrated management of blast as well as other major biotic constraints such as weeds needs to be further developed as blast populations present on wild rice and weeds appear to be closely related to rice pathogenic forms. Many of the current needs of the developing world, in particular, arise from a mixture of economic and social problems. Sustainable crop management approaches and improved varieties are essential if the doubling of agricultural output necessary for food security is to be achieved for a projected world population of eight billion or more by 2020. In this regard, scientists world-wide have embarked on various research strategies for rice blast management. For instance, using the ‘lineage exclusion’ strategy, cultivar Oryzica Llanos 5 has shown durable resistance to rice blast for over 10 years in Columbia. Recently, by planting mixed stands of rice cultivars with a different spectrum of resistance to M. grisea, considerable reduction in rice blast has been achieved in Yunnan province in China. Both these approaches are based on a sound understanding of the biodiversity of the pathogen populations. These management strategies, coupled with appropriate cultural practices including seed hygiene and continued disease monitoring, could lead to sustainable control of rice blast in developing countries.
Chipili, J.; Sreenivasaprasad, S.; Sere, Y.; Nutsugah, S.K.; Twumasi, J.; Brown, A.E.; Talbot, N.J. Rice blast pathogen population structure in West Africa for improved disease management. In: Plant Pathology and Global Food Security, BSPP Conference, Imperial College, London, 8-10 July 2002. (2002)