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Modulation of Light and Nitrogen for Quality-Traits Improvement: A Case Study of Altino Sweet Pepper

Local varieties are known to cope more efficiently with stressful and/or low-input conditions than cultivated ones by activating secondary metabolisms and, hence, are supposed to have higher nutraceutical potential. In this work, we investigate the effects of N and light, supplied at optimal and sub-optimal levels, on the fruit yield and quality of a local ecotype of sweet pepper, Altino, grown in the Abruzzo Region (Southern Italy). In 2017, two open-field experiments were carried out, comparing increasing N rates (0, 100 and 200 kg N ha−1, 0_N, 100_N and 200_N, respectively) and different percentages of shading and/or manipulations of the transmitted solar radiation, obtained through photoselective nets (red net, RN; black net, BN; unshaded Control). Both N and light were preconditions to obtain stable yields in terms of both fruit number and fruit weights. However, BN significantly reduced the number of sunscalded fruits (0.39 vs. 3.38 and 2.59 fruit plant−1 for BN, Control and RN, respectively), leading to lower waste. N deficiency favoured higher total polyphenol (TPC) and flavonoid (TFC) contents in ripened fruits; on the other hand, shading significantly reduced TPC (−12.4%) in immature and TFC (−18.2%) in red fruits. The variations in nutraceuticals were also evaluated in terms of the variations of the single phenolic acids in fruits during ripening; the most interesting results were associated with light treatments. Further research should be directed to the in-depth study of nutrition regimes, in combination with other photoselective nets applications (i.e., pearl nets), that could be suitable for the Altino genotype to enhance the yield and nutraceutical potentials of its fruits.