Safety of eucalyptus-based herbicides to crops - a study with Solanum lycopersicum L. as a model species

The development of eco-friendly herbicides is a crucial step towards sustainable agriculture. Over recent years, eucalyptus-based herbicides have been acknowledged as effective and promising strategies for weed management to reduce the application of synthetic herbicides, whose excessive use is associated with negative impacts in all environmental matrices. In previous studies, we developed two novel eucalyptus-based herbicides, EucaBio_solid (pre-emergent) and EucaBio_liquid (post-emergent), which showed strong herbicidal activities against Portulaca oleracea L. However, their safety for non-target species, including crops, remains unexplored. So, aiming to validate their potential as bioherbicides, the main goal of this study was to evaluate, for the first time, the environmental safety of EucaBio_solid and EucaBio_liquid on the growth and physiology of tomato plants (Solanum lycopersicum). For that, tomato plants were grown in soils where weeds (P. oleracea) have been previously treated with these two bioherbicides. As a positive control, S-metolachlor, a synthetic herbicide with pre- and post-emergent action, was used. After 23 days of growth, shoot and root length and biomass and the plant's redox status were analysed. Results showed that EucaBio_liquid had no negative effects on plant growth and even enhanced the shoot enzymatic antioxidant (AOX) system. Conversely, EucaBio_solid significantly inhibited plant growth by inducing oxidative stress, particularly in the roots, despite the activation of AOX defenses. These findings highlight EucaBio_liquid as a promising and eco-friendly alternative to synthetic herbicides, suitable for integration into sustainable weed management strategies.