Bacillus thuringiensis MG36 A POTENTIAL MICROBIOLIZATION AGENT FOR SOYBEAN SEEDS

The white mold caused by the fungus Sclerotinia sclerotiorum occurs in more than 400 species of plants and it has been considered as the second most important disease of soybean culture around the world. This disease is mainly controlled by chemical fungicides; however, the indiscriminate use of these compounds, has caused many problems and has increased too interest per investigations that look for alternatives of treatment for this pathology like the microbiolization. Thus, this study was designed to estimate the incidence of fungus Sclerotinea sclerotiorum on soybeans BMX Potência RR microbiolized with Bacillus thuringiensis MG36. For this, the statistical design adopted was DIC, where 150 seeds divided into three treatments, each one in five replicates with all results submitted to Tukey test (5%). The experimental procedures were initiated with the disinfestation of seeds by immersion in sodium hypochlorite solution (1%) for 1 min, followed by three washes of 1 min in sterile distilled water. Afterwards, one third of the seeds were submitted to microbiolization from contact with a bacterial suspension (OD540=0.5) from B. thuringiensis MG36, while other two thirds were submitted to treatment only with saline solution (0.85%); then, all the seeds were shaken in their respective recipient for 30 min (120 rpm, 28 ºC). Subsequently the seeds belonging to the three treatments were dried in a laminar flow chamber for 24 h and two of the three treatments were exposed to pathogens mycelium for 48 h. To evaluate the incidence of S. scleotiorumin in soybean seeds, the bromophenol agar medium (BDA with bromophenol blue - 150 mg/L, streptomycin sulfate - 150 mg/L and penicillin G - 150 mg/L) was selected. In this way, we obtained as result that the three treatments differed statistically from each other and that no seed from the negative control that was not microbiolized and was not exposed to phytophatogen was identified as contaminated. However, the treatment that was not microbiolized but exposed to the phytopathogen presented all contaminated seeds and only four seeds on average were identified as contaminated in the treatment where the seeds were microbiolized and exposed to the fungus mycelium. Thus, it was noted that in the soybean seeds there was a reduction in the contamination by S. scleotiorum in the order of 60%, confirming that B. thuringiensis can be considered a good candidate for future studies including greenhouses and open field experiments.