Effect of water regime, nitrogen level and biostimulants application on yield and quality traits of wild rocket [Diplotaxis tenuifolia (L.) DC.]

Wild rocket is an expanding vegetable crop, especially as a fresh-cut product that requires high quality standards. These can be achieved through appropriate management of agronomic practices such as water supply and nitrogen nutrition, in combination with emerging techniques such as the application of biostimulating substances. Hence, this study is focused on evaluating the response of the wild rocket to the application of two biostimulants in relation to different water regimes and nitrogen levels. The combined effect of two watering regimes (WR) (restoration of 50% and 100% of crop evapotranspiration-ETc, named WR50 and WR100, respectively); three N levels (NL) (0, 75 and 150 kg ha-1 N, named N0, N75 and N150, respectively); two biostimulants (BS) based on seaweed extract (SW), Azoxystrobin (AZ) and an untreated control (C) are investigated. The split-split plot experimental design with three replicates was used by arranging WR in the main plots, NL in the subplots and BS in the sub-subplots. Experiment was carried out in an unheated greenhouse during two growth cycles. Water shortage caused root biomass/total biomass ratio (RR) increase by 11.3% and 31.1% drop in yield, mainly because of the reduction in leaf size and number. Total phenols (TP), total antioxidant activity (TAA), total carotenoids (TCa) and nitrate (Ni) content were higher in WR50 in respect to WR100 by 10.4%, 18.7%, 12.0%, and 35.5%, respectively, while total chlorophyll (TCh) was lower by 5.3%. The increase of NL between N0 and N150 raised yield (222%), TCh (32.5%) and Ni (288.3), but reduced RR (43%), TP (16.2%), TAA (21.4%) and TCa (31.0%). SW and AZ increased yield respectively by 10.3% and 16.9%, mainly because raised leaf number for SW and leaf size for AZ. Moreover, SW increased RR by 7.2%, while AZ reduced it by 17.2%. SW and AZ improved TP, TAA, TCh and TCa respectively by 8.8%, 13.1%, 10.2% and 23.8% and by 10.8%, 19.7%, 16.0% and 35.6%. BS reduced Ni content by 21.5 (SW) and 36.8% (AZ). SW and AZ have shown good biostimulating efficacy by increasing yield and improving quality, reducing the harmful effects of water deficit. Tested BSs can be a useful tool for wild rocket farmers, especially under scarce water resources.