Crops grown under protected environment have had a great expansion in Brazil in the decade of 1990. In such environments soil is intensively and successively used and it may become infested with soilborne plant pathogens, such as Rhizoctonia solani, responsible for seedling damping-off and root rots of several plant species. In the present work soil solarization was used to the control of R. solani under greenhouse and field conditions. Four experiments were carried out, two in the summer of 1997/1998 and the other two in 1998/1999 in Piracicaba city, São Paulo state, Brazil (latitude 22º 42' and longitude 47º 38'). Nylon bags containing disinfested soil with propagules of R. solani AG4 (wheat grains previously colonized with the pathogen) were buried at 10 and 20 cm soil depth in solarized and non-solarized plots. After 20, 30, and 40 days in the two first experiments and 15, 30, and 45 days in the third and fourth experiments, the bags were removed from the soil. The grains were collected from the soil of each bag and placed in water-agar Petri dishes. After two days of incubation, grains showing typical growth of R. solani mycelium were assessed. Eradication of R. solani was accomplished after 20 to 30 days of soil solarization inside the greenhouse and after 30 to 45 days in the field, probably because in the protected environment the heat loss was smaller at night, since at 15:00 h the soil temperatures were similar in the solarized soils of both environments; with maximum of 49º C and medium temperatures between 40 and 45 º C, at 10 cm soil depth. In the non-solarized soil of the greenhouse the pathogen also lost its viability, although more slowly (40 days of treatment) than in the solarized plots.
soilborne pathogen; damping-off; soil disinfestation
