Bacillus subtilis, Trichoderma harzianum e microalga Parachlorella sp. atuam no biocontrole in vitro da Macrophomina phaseolina?

Abstract

Managing soil-borne pathogens represents a growing challenge in modern agriculture, especially given the persistence of species such as Macrophomina phaseolina, the causal agent of charcoal rot, which can survive for long periods in the soil through the formation of microsclerotia. In this context, the use of biological agents has been highlighted as a sustainable alternative to reduce dependence on chemical fungicides. This study aimed to evaluate the antagonistic potential of Bacillus subtilis and Trichoderma harzianum, alone or in combination, as well as the interaction of these microorganisms with the microalgae Parachlorella sp., in the in vitro control of M. phaseolina. The experiment was conducted in a randomized design, with two assays: (i) direct confrontation, to evaluate the effect of physical contact, and (ii) a volatile compound assay, to analyze the action of metabolites at a distance. The pathogen's mycelial growth rates, mycelial growth rate index (MGII), and area under the mycelial growth curve (AUCCM) were determined. In direct confrontation, T. harzianum reduced the mycelial growth of M. phaseolina by 61.3%, while B. subtilis promoted a 44.7% reduction. The combination between the two showed greater interference, with a 71.5% reduction compared to the control. In tests with volatile compounds, B. subtilis showed greater efficiency, improving AUCCM by 58.9%, followed by T. harzianum (46.2%) and the combination of both agents (65.4%). The presence of Parachlorella sp. did not present a direct antagonistic effect and partially impaired the efficiency of the microorganisms in physical confrontation (≈10% loss of deficiency), although it did not impair the tests with volatiles. The results demonstrate that B. subtilis and T. harzianum are effective in biocontrolling M. phaseolina, exhibiting complementary mechanisms: mycoparasitism and competition for T. harzianum, and production of volatile compounds for B. subtilis. The combination of both enhanced the control effects, reducing synergism. The microalgae displayed neutral or slightly competitive behavior, requiring further evaluation under field conditions. It is concluded that the use of antagonistic microorganisms represents a viable and sustainable alternative for control of M. phaseolina in vivo.