Analysis and Mapping of the Spatial Spread of African Cassava Mosaic Virus Using Geostatistics and the Kriging Technique

Lecoustre, R., Fargette, D., Fauquet, C., and de Reffye, P. 1989. Analysis and mapping of the spatial spread of African cassava mosaic virus using geostatistics and the kriging technique. Phytopathology 79: 913-920. Theories of regionalized variables and kriging were used to assess the incidence along the wind-exposed southwest field borders, disease spatial pattern of African cassava mosaic virus (ACMV). A linearlike gradients, and other less obvious features. Up to 60% of the total variance semivariogram without a range characterizes the ACMV distribution and was reconstructed from a 7% sample. Kriging was successfully applied indicates a strongly spatially dependent structure with limited random to characterize the spatial pattern of spread in cassava fields differing variation. Oriented semivariograms reveal a strong anisotropy in relation in planting date, size, arrangement, orientation, and method of sampling. to the prevailing wind direction. Further features of the semivariogram This technique was also efficient when the pattern of spread was and comparisons of semivariograms between fields and between surveys heterogenous, although more intensive surveys were then required. provide additional information and support various hypotheses on the Practical applications of geostatistics and kriging in epidemiology are pattern of spread. From a sample of limited size, kriging reproduced discussed. the main characteristics of the spatial pattern of spread, including higher Spatial patterns of disease level can provide important clues and pedology (21). to the ecology of disease (e.g., direction and distance of spread, African cassava mosaic disease is caused by a whitefly-borne importance and proximity of the sources of virus and vectors, geminivirus (2). The spatial patterns of spread of this disease vector mobility) (20). Patterns must be considered in designing have been studied intensively in the Ivory Coast (5,6) and are sampling methods and sound control measures (8,20). Hence, mainly characterized by gradients oriented in the direction of efficient methods of analysis and interpretation of spatial pattern the prevailing southwest wind. In this article, the theory of are needed to provide the greatest possible information in relation regionalized variables is used to assess the spatial patterns of to the time and effort involved. Past studies of spatial patterns the spread of African cassava mosaic virus (ACMV) in various have relied mostly on methods based on the examination of the cassava fields that differ in total area, subplot size, planting dates, mean and variance or on the frequency distribution of observed and orientation. We also describe the application of kriging to