Interactive effect of water regime, nitrogen rate and biostimulant application on physiological and biochemical traits of wild rocket

A research was carried out to evaluate the biostimulating effects of Azoxystrobin (Azo+) and a brown seaweed extract (SW+) on wild rocket grown during two crop cycles in pots placed in a cold greenhouse. Two watering regimes were applied (restoring 50% and 100% of crop evapotranspiration, indicated respectively WR50 and WR100) along with three N levels (0, 75 and 150 kg ha-1 of N). The experimental layout was a split-split plot with three replications, arranging water regimes in the main plots, N levels in the plots and biostimulants in the subplots. The paper reports the results related to the effects on i) leaf chlorophyll content (Chl), ii) parameters related to gas exchanges including net assimilation (A), transpiration (T), stomatal conductance (gs), internal CO2 concentration (Ci) and intrinsic water use efficiency (WUEi), iii) some enzymes involved in oxidative stress including superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT). The water deficit led to a drop in A and T, an increase in WUEi and in the antioxidant enzymes content of wild rocket. Chl rised with the N availability increase. The increase in N level caused the rise of A and T in WR100 while it exacerbated the negative effect of water deficit in WR50. Azo+ caused 15.0% increase in A, 13.4% drop in gs and 33.5% rise in WUEi. Additionally, Azo+ increased by 8.7% Chl and by 489%, 112%, 193%, and 336% SOD, POD, APX and CAT, respectively. SW+ improved A (+7.9%), WUEi (+14.9%), Chl (+6.1%), SOD (+395%), POD (+160%), APX (+155%) and CAT (+334%). The increase in antioxidant enzymes after the application of Azo+ and SW+ was greater under water deficit. The wild rocket benefited of Azo+ and SW+ application, which stimulated the biosynthesis of chlorophyll and antioxidant enzymes, demonstrating the potential role in limiting water stress. Therefore, the two biostimulants can represent a useful tool to improve the production of wild rocket and increase the water use efficiency.