Possible use of moringa as a biostimulant for vegetable and flower crops

In recent years, a new, innovative, environmentally friendly approach has been the application of natural plant biostimulants (PBs) to various crops. Natural biostimulants of plant origin (plant-derived biostimulants, PDBs; e.g., licorice, borage, aloe, Lawsonia inermis, Moringa oleifera, etc.) have confirmed to be able to stimulate plant growth, increasing the efficiency of use of nutrients and improving their tolerance to biotic and abiotic stress. M. oleifera, among all PDBs, deserves particular attention because it is a rich source of hormones, antioxidants, vitamins, and mineral nutrients. Different trials on vegetable and flower crops were carried out to understand the effects of moringa leaf extract (MLE). In two microgreens species (turnip greens and radish) four treatments based on biostimulants [Bio-1: Trainer®; Bio-2: Aquamin®; Bio-3: leaf moringa extract; C: distilled water (control)] were applied. Biostimulant treatments showed a positive effect on microgreens and, in particular, on radish, thereby improving various nutraceutical parameters. To evaluate the effect of MLE treatment on the baby leaves of Brassica species, two trials were conducted. In the first on radish baby leaves, the application of MLE at the dose 1:30 (v:v) resulted in significant increases even greater than 35% of leaf area and fresh epigeous biomass. In the second trial, a cultivar of leafy cabbage ‘Cavolo Laciniato Nero di Toscana’ (CL) and a Sicilian landrace of broccoli ‘Broccolo Nero’ (BN) were used. The MLE treatment resulted in significant and contrasting changes in the nutraceutical characteristics of the two genotypes, demonstrating a species-specific effect. To understand the effects of MLE application on ornamental plants under stress conditions, a trial was conducted on petunia plants. Plants were subjected to different levels of drought stress and treated with MLE. Leaf moringa application improved drought resistance and reduced water deficit effects, modifying growth parameters, proline and malondialdehyde content, and enzyme activity. These positive effects were linked to promoting the activity of antioxidant enzymes and increasing the content of phenols, flavonols, and osmolytes, which reduced the levels of reactive oxygen species, malondialdehyde, and electrolyte leakage. Further research is required to expand our knowledge of this mode of action. In different crops, it emerges how MLE can represent a sustainable tool to make cultivation systems more productive and efficient and, above all, with less negative impacts on the environment.