Although there is a risk of soil being contaminated with plant pathogen inocula its uses in the substrate composition is the most economical and useful practice for fruit propagation in general. In this work, looking for an alternative method besides the methyl bromide fumigation for soil sterilization the efficiency of solar collector devices for substrate disinfestations in the elimination of S. rolfsii sclerotia was evaluated. The assays were realized in three dates: October 6th and 25th and December 13th of 2000. For evaluation of the sclerotia viability the sclerotia recovered from the soil treated in solar collector were sown in culture medium and submitted to the tetrazolium staining test (tetrazolium triphenil-chloride). The tetrazolium coloration was used to confirm if non-germinated sclerotia were really heat inactivated or if there was fungistase induction. In the first assay during a cloudy day, the maximum temperature reached in the substrate was 45ºC and the germination of sclerotia was null and accompanied by 100% of bacteria colonization. In the two last dates of evaluation during sunny days the maximum temperatures in the substrate varied from 60 to 80ºC and the sclerotia were 100% eradicated with only one day-treatment. The staining test with TTC confirmed that non-germinated sclerotia were heat inactivated by the absence of red color due to the dehydrogenase activity inhibition (enzymatic denaturation). It was concluded that even under sub-optimum conditions for substrate treatment in solar collector devices the long exposition to higher temperatures were enough to cause severe injuries in the pathogen sclerotia which became vulnerable to microbial antagonism. The solar collector devices were efficient for substrate disinfestations and for the control of S. rolfsii in the evaluated conditions.
Sclerotium rolfsii; solarization; sclerotia; substrate
