Abstract
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 (Diplotaxis tenuifolia (L.) DC.), comparing three biostimulant treatments (legume-derived protein hydrolysates, Trichoderma harzianum T22, and protein hydrolysates + Trichoderma harzianum 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 + Trichoderma applications, which also increased the colorimetric parameters compared to the untreated control. The treatment with protein hydrolysates + Trichoderma 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 + Trichoderma 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 Trichoderma 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.
Highlights
Perennial wall rocket (Diplotaxis tenuifolia (L.) DC.) is a leafy vegetable species that has been increasingly cultivated in the Mediterranean area in the past two decades, accounting for a surface area of 4000 ha of horticultural production in Italy [1]
No significant differences were noted in the number of Trichoderma colony forming units (CFU)
The CFU of Trichoderma in soil samples collected from the rhizosphere of wall rocket at the end of the experiment demonstrated a significantly greater abundance in the treatments where the beneficial microbe was applied to the plants in comparison to those of the untreated control and Plants 2020, 9, x FOR PEER REVIEW
Summary
Perennial wall rocket (Diplotaxis tenuifolia (L.) DC.) is a leafy vegetable species that has been increasingly cultivated in the Mediterranean area in the past two decades, accounting for a surface area of 4000 ha of horticultural production in Italy [1]. The leaves are mainly used raw and in salads, and this product has found a worldwide diffusion in both the fresh and baby leaf oriented grocery markets This produce is appreciated by the consumer for its pungent “peppery” taste, and for its high beneficial nutritional and antioxidant components, which are noted functions in the prevention of cardiovascular and carcinogenic diseases [2]. D. tenuifolia is mostly cultivated in greenhouses and the crop cycles are usually managed from early autumn to spring or from spring to summer, depending on farming systems, growing area, and commercial demand [1,2]. Five to six crop cycles are possible, each with a duration of 20 to 100 days after planting or regrowth, according to the time frame. The longest period occurs in winter due to the lower temperatures and light intensity, which result in slower plant growth [1,2]
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