Prospection of microorganisms and evaluation of methodologies for maximizing phytotoxic activity for the development of bioherbicides

Weeds are one of the main problems in agriculture. They compete with the culture of interest for resources such as water, light, and nutrients. In modern agriculture, chemical herbicides are the most widely used method for weed control. The too much use of these herbicides has generated great concerns about the environment, due to food contamination, environmental pollution, weed resistance, among others. In this context, the present work proposed to prospect microorganisms capable of producing secondary metabolites with herbicide activity in weeds. For this, a field search was performed for weeds with symptoms of diseases, resulting in the isolation of sixty-three microorganisms. The bioherbicide activity was first evaluated in seeds and plants of Cucumis sativus and seeds of Avena strigosa. The crude broths of microorganisms with the best results were tested in weeds: Amaranthus hybridus, Echinochloa crusgalli, Conyza sp., and Bidens pilosa. After that, weeds with greater sensitivity to treatments (A. hybridus, E. crusgalli) were selected for the sequence of experiments, where different methods were used to extract and potentiate secondary metabolites (ultrasound, cocultivation and increased dose applied). A preliminary study was carried out for the development of formulations with the most promising broths, using different oils (soybean, sunflower, and mineral) and the surfactant Break-Thru® and Tween®80 as adjuvants. The formulations using soybean oil presented the best results in tests with detached leaf and were used in the in vivo tests against A. hybridus and E. crusgalli. Phytotoxicity in tests with formulations reached 70% for E. crusgalli and 30% for A. hybridus, with a dose equivalent to 600 L ha−1 . The microorganisms identified by the molecular analysis were: Nigrospora sphaerica, Bacillus velezensis, and Aspergillus flavus.