Areas from a microbasin without the incidence of plant diseases caused by Rhizoctonia solani GA 4 were statistically grouped by Ward's method, in relation to soil suppressiveness, described by the mycelial growth rate. A gradient of suppressiveness was defined between the groups. The relationship between suppressiveness and types of vegetation was described by a multiple correspondence analysis. In general, soils from pasture, fallow ground and forest were classified as suppressive soils, while sugar cane (Saccharum officinarum), maize (Zea mays ), coffee (Coffea arabica) and ploughed soils, as conducive soils. However, results showed that other factors affect suppressiveness besides vegetation. A biocide treatment (fumigation) promoted a greater increase in the growth rate of the pathogen on suppressive soils than on conducive ones
