Yield

Agricultural yield is the main agronomic parameter indicating productivity in crops (^{Schroeder et al., 1997}). In this paper, significant yield differences were obtained between evaluated varieties, mainly between grafted and non-grafted plants (Figure 1). The varieties with the highest production were Fascinato grafted with Terrano and Janette grafted with Terrano, obtaining an increase of 53.47% and 49.40% respectively in relation to the same ungrafted varieties, which coincides with ^{Godoy (2007)}, who describes that in results obtained In Seokwang tomato grafted with two different patterns, the increase in yield was 54 and 51%, respectively. ^{Ruiz et al. (1997)} found significant differences in yield between the grafted and ungrafted Yuma and Gallicum melon varieties on three different rootstocks where the Kamel rootstock showed the highest yield with both varieties. In our study, yield was significantly influenced by the interaction between grafts and rootstock, coinciding with ^{Zijlstra et al. (1994)}, who mention that the rootstock determines the yield in the grafted plants.

Figure 1 Effect of the variety-rootstock combination on the total production of bell pepper. The vertical lines in each bar correspond to the standard deviation. Averages with equal letters in each bar are not statistically different (LSD, 0.05).  

Nitrogen nutritional dynamics (N)

Nitrogen is the mineral element that plants require in large quantities and is considered the limiting nutrient for crop growth and yield, in addition to being the most studied fertilizer (^{Marschner, 1995}). In this study, the nitrogen concentration of the non-grafted varieties exceeded the values obtained in the same grafted varieties during the first phenological stages of the crop, however, it was observed that the grafted varieties increased the concentration with respect to those not grafted (Figure 2A), coinciding with ^{Ruiz et al. (1997)}, who found that the use of the Kamel rootstock with the Yuma variety in melon plants reduced nitrogen uptake by less than 25%, as did the Gallicum variety on the RS-841 rootstock.

Figure 2 Effect of rootstock use on the nutritional dynamics of macronutrients in bell pepper: A) nitrogen; B) phosphorus; C) potassium; D) calcium; E) magnesium; and F) sodium. T₁= Janette without graft; T₂= Janette grafted with Terrano; T₃= Fascinato without graft; T₄= Fascinato grafted with Terrano.  

In addition, the use of different rootstock genotypes caused little change in the macronutrient foliar content, mainly in N. On the other hand, it was observed that the obtained values of N with respect to the reference values by ^{Mills and Jones (1991)}, indicate that they are below the sufficiency range (3.5-5%). This is probably due to the fact that the grafted varieties are more productive and therefore demand more N, being this element associated to crops’ development and yield.

Nutritional dynamics of phosphorus (P)

Phosphorus is an essential element for higher plants, is required in higher concentrations in tissues and is particularly indispensable during vegetative growth (^{Mengel and Kirkby, 2001}). In this paper, the nutritional dynamics of P showed differences in the concentration of this element between the grafted and ungrafted Janette and Fascinato varieties, standing out in the Janette-Terrano variety, which showed an increase of 10.81% in its concentration due to the influence of rootstock, mainly after harvest (Figure 2B), coinciding with ^{Ruiz et al. (1996)}, who mention that the use of rootstocks in melon plants can improve some morphological and physiological characteristics to increase the soil P uptake and its translocation towards the leaves of the graft. Similar case reported ^{Ruiz et al. (1997)}, who describe that regardless of the pattern used, P concentrations in grafted melon plants were higher than in non-grafted varieties, coinciding with ^{Contreras (2014)}, who found significant differences in favor of grafted tomato plants, showing a 6.83% increase in P concentration in relation to ungrafted plants.

On the other hand, ^{Mills and Jones (1991)}, mention that the sufficiency range of P in bell pepper is 0.22-0.7%. In this paper, the grafted and ungrafted Janette and Fascinato varieties were below the sufficiency range. However, P levels were not limiting in the production of bell pepper, since the variety Fascinato grafted with Terrano was the most productive, followed by the variety Janette grafted with Terrano.

Nutritional dynamics of potassium (K)

K is an essential macronutrient required in large quantities for normal growth and development of crops. Some of the main functions of plants where K is involved are: osmoregulation, starch synthesis, enzyme activation, protein synthesis, stomatal movement and ionic balance (^{Marschner, 1995}). For a good growth and development of bell pepper, the sufficiency range of K stands for 3.5-4.5% (^{Mills and Jones, 1991}), which indicates that in this paper values were obtained below the sufficiency range in both grafted and non-grafted varieties (Figure 2C). However, the dynamics presented by K were stable for all varieties of evaluated bell pepper. ^{Godoy et al. (2008)}, observed a higher concentration of K in grafted tomato plants (35%), as did ^{Ruiz et al. (1997)} reported that K levels in grafted melon plants decreased from non-grafted plants by as much as 52%. However, in this paper the effect of rootstock and low K level on reference values were not limiting on the yield of bell pepper.

Nutritional dynamics of calcium (Ca)

Ca is an essential nutrient for plants. As a divalent cation, it is required for the structural functions of the cell wall and membranes, as a counter-cation of inorganic and organic anions in the vacuole (^{Mengel and Kirkby, 2001}). In the leaf analysis for Ca, significant differences were observed among the varieties evaluated by effect of the rootstock. The Fascinato-Terrano variety showed a positive influence on the concentration of Ca from the harvest (August 20^th), while the Janette-Terrano variety decreased its concentration with respect to the same ungrafted variety. It is important to emphasize that in all varieties a decrease in the foliar concentration at the end of the cycle was shown (Figure 2D), contrary to the one described by ^{Noh-Medina et al. (2010)}, who mention that the concentration of Ca in ungrafted habanero chile, decreases with respect to the maturity of the plants. ^{Godoy et al. (2008)}, found that the Gironde variety grafted with Maxifort on tomato plants, showed higher concentration of Ca with respect to the same ungrafted variety, however, ^{Contreras (2014)} reported that no significant differences were found due to the grafting effect in the Ca concentration in tomato plants.

On the other hand, ^{Mills and Jones (1991)} report that the optimal sufficiency values for Ca in bell pepper is 1.3-2.8%, reaching the Terrano grafted and ungrafted Fascinato varieties, an optimum point for Ca in the harvest stage.

Nutritional dynamics of magnesium (Mg)

The most known role of magnesium (Mg) in plants is their presence in the center of the chlorophyll molecule and for this reason is essential for photosynthesis, it is also involved in protein metabolism (^{Marschner, 1995}). In this paper, the nutritional analysis of Mg showed constant dynamics for all the evaluated varieties, with an increase in the concentration at the end of the production cycle, emphasizing in the grafted Janette and Fascinato varieties. ^{Ruiz et al. (1997)} observed that in grafted melon plants, the concentration of Mg decreased with respect to the non-grafted, coinciding with ^{Godoy et al. (2008)}, who observed that the concentration of Mg was significantly lower in grafted tomato plants. In this paper, it was determined that the use of Terrano rootstock positively influences the concentration of Mg in the Fascinato and Janette varieties.

On the other hand, the obtained values of Mg concentration in the evaluated varieties were considered within the sufficiency range according to ^{Mills and Jones (1991)}, who describe it for bell pepper the range is of 0.3-2.8%.

Nutritional dynamics of sodium (Na)

Sodium stimulates growth through cell elongation and can replace potassium as an osmotically active solute (^{Mengel and Kirkby, 2001}). In this study, the values obtained show that the Janette and Fascinato grafted varieties have a lower level of Na than the ungrafted ones (Figure 2F). The highest demand for Na was shown at the harvest stage, with the grafted Fascinato and Janette varieties standing out.

According to ^{Mills and Jones (1991)}, the Na is considered a nonessential element, therefore they do not present data of its sufficiency range in bell pepper.