Micro-scale Systematic Sampling of Soil: Heterogeneity in Populations of Fusarium oxysporum, F. solani, F. roseum and F. moniliforme

The variability of Fusarium spp. density in soil was stu- died in a ®eld located in Badajoz (south-western Spain). The upper 40 cm of each side of a 1m 1m 1m pit were sampled intensively, taking soil samples from points 10 cm apart. The species isolated were F. oxysporum, F. solani, F. roseum and F. moniliforme. For all four sides of the pit population densities of F. oxysporum, F. solani and F. roseum signi®cantly decreased with increasing soil depth and for all the four layers signi®cant di€erences were detected between sides of the pit. Horizontal variability also occurred on a smaller sampling scale: when a layer of a side was sampled, densities might be signi®cantly di€erent between points in the layer. However, no clear trend in horizontal variability was observed for any species. These ®ndings demonstrate that Fusarium spp. popula- tions were heterogeneously distributed in this reduced soil volum