## 4 Discussion  
Use of grafting is a good tool to improve vegetable production in areas where biotic-abiotic stresses can seriously determine reductions in not only crop yield, but also in production quality [50; 51; 52]. In this way, most research aims to assess the rootstock and scion interaction and the effect that this interaction has on both agronomic performance and stress resistance [10; 14; 53]. However, in recent years, many works report the effect of grafting on the production of vegetable quality, particularly the physico-chemical, nutritional and nutraceuticaltical properties of the fruit produced by grafted plants [10; 18; 29; 30]. Fruit quality is a set of attributes that determine consumer choice, which  
Figure 5: Discrimination of the VOCs of the green fruit based on the canonical discriminant analysis. Figure 6: Discrimination of the VOCs of the red fruit on the basis of the canonical discriminant analysis. **4**: SUECA_ungrafted; \(\Delta\): SUECA_grafted; **v**: “Valencia”_ungrafted; V: “Valencia”_grafted; \(\bullet\): “Cuerno”_ungrafted; \(\circ\): Cuerno_grafted. can be divided into external fruit aspect, nutritional and nutraceuticaltical characteristics [54]. These last properties have been assumed to be of particular importance for consumers given the positive relations between fruit/vegetables and human health [55; 56]. Many studies report that a healthy diet rich in fruit and vegetables, named functional food, helps to delay senescence processes in humans, but to also reduce the risk of important pathologies including cancer and cardiovascular diseases [56; 57; 58]. The important characteristic of functional food is its richness in antioxidant compounds, capable of scavenging ROS based on cellular oxidative stress [25]. Sweet pepper fruit falls in the category of functional foods because it is rich in ascorbic acid, caroten, phenols, and also in capsaicinoids, xanthophylls, and flavonoids and is, for this reason, characterized by high antioxidant capacity [27; 28]. However, the amount of phytochemicals in peppers depends on many factors, including rootstock, although literature reports opposite results about the influence of grafting on the amount of phytochemicals in peppers. Our study evidenced for all three landraces that grafting positively influenced marketable yield, whereas no differences were found among the three landraces. The higher yield in the sweet peppers from the grafted plants has already been demonstrated [14; 59] and is attributable to an increase in the average number of fruit per plant. This increase can be related to the more vigorous root system of rootstock NIBER(r) that, in turn, induces an increase in water and nutrient uptake [31; 32]. In addition, non-marketable yields and fruit with BER markedly dropped because grafting further increased production due to fewer losses. The minor incidence of fruit with BER symptoms caused by the grafted plants could be attributed to the rootstock better resisting abiotic stress, as previously reported in this species by [PERSON] et al. [60], [PERSON] et al. [61] and [PERSON] et al. [13; 33]. In addition to increased fruit production, the physico-chemical characteristics remained the same, or even improved, for the studied rootstock. Fruit dry matter was similar in the green fruit, or increased in the red fruit, of the three different pepper landraces grafted onto NIBER(r) compared to the fruit from the ungrafted plants, whereas no changes were recorded for pulp thickness. Other authors have found similar results [19], showing that an increment in dry matter could be attributed to the higher uptake and transport of mineral elements [62; 63]. The perception of pepper fruit sourness is related to titratable acidity. Grafting also increased titratable acidity in both red and green fruit, which is an important factor for fruit quality if we consider the role played by acids in the flavor of fresh pepper products.