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Effects of Tillage on the Spatial Pattern of Microsclerotia of Macrophomina phaseolina. O. M. Olanya, Graduate student, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616; C. Lee Campbell, Associate professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 78:217-221. Accepted for publication 7 September 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-217.

The effects of soil tillage on the spatial pattern of sclerotia of Macrophomina phaseolina were investigated at eight sites in 8- × 8-m grids divided into 64 1- × 1-m contiguous quadrats. One soil core (2.5 × 10–14 cm) was removed from the center of each quadrat before tillage and after one or two diskings. Inoculum density (ID) was determined by assaying a 10-g subsample of air-dried soil using a selective assay procedure. Mean ID was similar among tillage treatments within a site and, based on values of Morisita’s index, low to moderate aggregation of inoculum was detected consistently. Aggregation of propagules decreased after one tillage operation at most locations. Physical redistribution of inoculum by disking was most evident in plots with high initial inoculum density and a high degree of initial aggregation of inoculum.