Could biostimulants with plant active compounds improve the tolerance to oxidative stress in Prosopis alba?

Biostimulants are considered as an important source of bioactive compounds that applied to plants can improve their stress tolerance and could enhance their crop quality traits. However, the activity of biostimulants obtained from plants is less known compared with other kind of biostimulants applied to plants. The aim of this work was to explore the potential of four phytoextracts derived from species with recognized antioxidant activity and/or rich in polysaccharides as plant biostimulants of seedlings of Prosopis alba. P. alba is an Argentinean native species widely distributed in arid and semi-arid areas which is relevant for the restoration and reforestation of degraded areas. The selected species for the natural extracts and their concentration were: Ilex paraguariensis (2% w/v), Larrea divaricata (2% w/v), Schinopsis lorentzii (2% w/v) and Aloe vera (0.1% w/v). In this study, the concentration of malondialdehyde (MDA), an oxidative stress biomarker, was measured every week in control and rustified seedlings along the rustification stage (RS) to monitor the oxidative stress condition. In a second assay, each natural extract was foliarly sprayed after 7 and 14 days since the beginning of the RS. MDA was measured at 21 days after RS begining as preliminary results showed a significant accumulation of MDA in rustified seedlings compared with control seedlings at this time. As main results, rustified seedlings sprayed with I. paraguariensis and L. divaricata showed lower MDA concentration than rustified seedlings without any extract application. Both extracts were characterized by their antioxidant activity. These results suggest that natural extracts of I. paraguariensis and L. divaricata could be considered potential plant biostimulant which reduce oxidative stress biomarkers in P. alba. Thus, in seedlings treated with these biostimulant extracts, the ROS increase rate due to RS seemed to be lower than its clearance rate by endogenous antioxidants.