*3.3. E*ff*ects of Grafting Combination and Mycorrhizal Inoculation on the Mineral Profile and Nutritional and Functional Quality*

Neither the grafting combination nor mycorrhizal inoculation had a significant effect on the fruit dry matter content (DM). The soluble solids content (SSC) and K content of eggplant fruits in the B/T and B/M plots, averaged across mycorrhizal inoculation status, were higher than those for the other grafting combinations (Table 2).

**Table 2.** Main effects of the grafting combination and AM inoculation on the fruit dry matter (DM) percentage, soluble solids content (SSC) and macromineral content of greenhouse eggplant.


NS, \*\*\* non-significant or significant at *p* ≤ 0.001. Data represent mean values of three replicates. Values within a column followed by the same letter are not significantly different at *p* ≤ 0.05 according to Tukey's HSD Test. NS = not significant. +AM, −AM = mycorrhizal and non-mycorrhizal eggplants, respectively.

The highest and lowest Ca and mg fruit contents were recorded in the B/P and B/T plots, respectively. Regardless of the grafting combination, the SSC and K fruit contents in the inoculated plots were 11.4% and 11.4% higher than in the non-inoculated ones, respectively. No significant interaction was observed between the grafting combination and mycorrhizal inoculation in terms of the DM percentage; SSC; and K, Ca and mg fruit contents (Table 2).

The grafting combination and mycorrhizal inoculation significantly affected the P and Fe fruit contents, protein content, firmness, ascorbic acid, total anthocyanins, chlorogenic acid and glycoalkaloids (Table 3).


*p* ≤ 0.05 according to Tukey's HSD Test. NS = not significant. +AM, −AM =

mycorrhizal and

non-mycorrhizal

 eggplants, respectively.

#### *Agronomy* **2020** , *10*, 693

The inoculation treatment elicited a significant increase in the P fruit content in the B/P and B/T plots compared to in the non-inoculated ones. However, this effect was not apparent with the other grafting combinations.

A similar positive effect was also observed in eggplant grafted onto *S. paniculatum*, since mycorrhizal inoculation increased Fe concentration in inoculated plants compared to in the non-inoculated ones (Table 3). Moreover, eggplant "Birgah" grafted onto *S. torvum* and inoculated with AM fungi displayed the highest total protein value (Table 3). Except for the B/T grafting combination where no significant changes in fruit firmness were observed, the inoculation of eggplant with AM fungi in all the other grafting combinations (ungrafted, B/B, B/M and B/P) incurred a significant increase in fruit firmness (Table 3). Contrarily, for the latter quality parameters (P, Fe, protein and firmness), the beneficial effect of AM fungi inoculation on ascorbic acid in eggplant fruits was apparent with all the grafting combinations tested, with the highest values recorded for "Birgah" grafted onto *S. torvum* (Table 3).

The total anthocyanin and chlorogenic acid contents ranged from 7154 to 11,162 and 757 to 1027 mg 100 g−<sup>1</sup> dw, respectively. Interestingly, the B/P grafting combination inoculated with AM fungi produced a major amplification of total anthocyanins and chlorogenic acid in comparison to the rest of the treatments (Table 3). Finally, the results indicated that the highest glycoalkaloid content was observed in the non-inoculated B/M grafting combination, whereas the lowest values were recorded in the B/P and B/T combinations inoculated with *R. irregularis* (Table 3).

#### *3.4. Principal Component Analysis of All Agronomic and Qualitative Parameters*

The principal component analysis (PCA) on the agronomic and qualitative traits of greenhouse eggplant in response to the grafting combination and mycorrhizal inoculation is reported in Figure 2.

**Figure 2.** Principal component loading plot and scores of the principal component analysis (PCA) of the yield, yield components, nitrogen use efficiency (NUE), dry matter percentage (DM), protein, firmness, soluble solids content (SSC), minerals (P, K, Ca, mg and Fe), bioactive molecules (ascorbic acid, anthocyanins and chlorogenic acid) and glycoalkaloids of eggplant cv. "Birgah" as a function of grafting combination (ungrafted B and self-grafted B/B, B/T, B/M and B/P) and AM inoculation (+AM and –AM).

The first four PCs (i.e., principal components) were related with eigenvalues higher than 1 and explained 94.7% of the total variance (Table 4).


**Table 4.** Correlation coefficients for each agronomic and qualitative traits, eigenvalues, variance and cumulative proportions of total variance of the four principal components (PCs).

In the current greenhouse experiment, the loading matrix indicates that variation in Ca and K was most closely aligned with the total anthocyanins, whereas the variation in the glycoalkaloids was not correlated to the SSC (Figure 2). The score plot of the PCA superimposed on the agronomic and qualitative parameters demonstrated a strong clustering of the two mycorrhizal treatments along PC1 (with the exception of *S. torvum* × −AM), with +AM plants concentrating marketable yield, NUE, DM, SSC, mineral composition and ascorbic acid (Figure 2). Particularly, the B/T grafting combination inoculated with AM fungi was positioned on the positive side of PC1 in the lower right quadrant of the PCA score plot, and it exhibited the highest crop performance (high yield, number of fruits and NUE) with premium quality due to high concentrations of DM, SSC and ascorbic acid (Figure 2). Moreover, eggplant grafted onto *S. paniculatum* and inoculated with AM was characterized by higher P, Fe and total anthocyanin content (Figure 2). Finally, non-inoculated ungrafted and self-grafted plants were positioned in the lower left quadrant, characterized by higher glycoalkaloid content (Figure 2).
