<i>Diplotaxis tenuifolia</i> (L.) DC. Yield and Quality as Influenced by Cropping Season, Protein Hydrolysates, and <i>Trichoderma</i> Applications

Increasing attention is being given to plant biostimulants as a sustainable farming practice aimed to enhance vegetable crop performance. This research was conducted on greenhouse-grown perennial wall rocket (<i>Diplotaxis tenuifolia</i> (L.) DC.), comparing three biostimulant treatments (legume-derived protein hydrolysates, <i>Trichoderma harzianum</i> T22, and protein hydrolysates + <i>Trichoderma harzianum</i> T22) plus an untreated control, in a factorial combination with three cropping seasons (autumn–winter, winter, winter–spring). Measurements were performed on leaf yield components, colorimetric indicators, mineral composition, bioactive compounds, and antioxidant activity. Leaf marketable yield and mean weight, as well as plant dry weight, showed the highest values in winter crop cycle. Biostimulant treatments resulted in 18.4% and 26.4% increase in leaf yield and number of leaves per rosette, respectively, compared to the untreated control. Protein hydrolysates led to the highest plant dry weight (+34.7% compared to the control). Soil plant analysis development (SPAD) index as well as NO₃, PO₄, SO₄, and Ca contents were influenced more during the winter–spring season than the winter cropping season. The winter production season resulted in a 19.8% increase in the leaf lipophilic antioxidant activity, whereas the hydrophilic antioxidant activity was 34.9% higher during the winter–spring season. SPAD index was the highest with protein hydrolysates + <i>Trichoderma</i> applications, which also increased the colorimetric parameters compared to the untreated control. The treatment with protein hydrolysates + <i>Trichoderma</i> enhanced N, PO₄, Mg, and Na contents, compared to both biostimulants applied singly and to the untreated control. Both biostimulants applied alone or the protein hydrolysates + <i>Trichoderma</i> combination led to the increase of the lipophilic and hydrophilic antioxidant activity, as well as ascorbic acid and chlorophyll b, compared to the untreated control. The present research revealed that protein hydrolysates and <i>Trichoderma</i> single applications, and even more their combination in the case of some nutrients content, represent an effective tool for enhancing the yield and the quality attributes of perennial wall rocket produced under the perspective of sustainable crop system.