Interactive Effect of Nitrogen and Azoxystrobin on Yield, Quality, Nitrogen and Water Use Efficiency of Wild Rocket in Southern Italy

Wild rocket (<i>Diplotaxis tenuifolia</i> L. DC) is an emerging vegetable which market requires high-quality standards that can be obtained through appropriate cultivation techniques such as the right level of nitrogen and the application of biostimulant substances. These include strobilurins, marketed mainly as fungicides that can have complementary positive effects on the yield, quality and resources’ use efficiency of many crops. For this reason, a trial in an unheated greenhouse, in Southern Italy, to evaluate the possibility of using Azoxystrobin to improve the production of wild rocket subjected to different nitrogen inputs, was carried out. Two N levels (40 and 140 kg ha⁻¹), Azoxystrobin-based biostimulant (Azo+) and control without Azoxystrobin (Azo−) were compared. The yield, morphological characteristics, nitrogen and water use efficiency (NUE, WUE), antioxidant activity, the content of dry matter, chlorophyll, carotenoids, phenols, and nitrates were assessed. A higher N level resulted in a 16.3% yield increase that was matched by a 12.5% reduction in NUE, 15.8, 7.3, and 16.1% increases in yield WUE (Y_WUE), biomass WUE (B_WUE), and irrigation yield WUE (IY_WUE), respectively, and a worsening of some qualitative characteristics such as a 8.5% rise in nitrates, and a decline by 11.5, 10.1, and 26.1% in the carotenoids, phenols, and antioxidant activity, respectively. Azo+ increased the yield by 10.3%, NUE by 8.9%, and Y_WUE, B_WUE, and IY_WUE, by 13.9, 9.1, and 13.8% respectively. Moreover, Azo+ improved some qualitative characteristics such as total phenols (+9.4%), chlorophyll (+15.2%), carotenoids (+9.7%), and antioxidant activity (+17.4%), while it did not affect the nitrate content. Azoxystrobin can be an additional tool available for farmers to ensure high-quality standards of wild rocket.