## 4 Discussion
### Principal Component Analysis  
Principal component analysis (PCA) was performed to identify the main parameters of the studied agro-morphological traits that could be used to evaluate and select the most appropriate salinity level, nutrient, and grafting conditions (Figure 3). The first three principal components (F1, F2, and F3) explained 94.31% of the phenotypic variation and covered all measured traits (Table 10). The first two principal components (F1 and F2) had eigenvalues greater than 7.5 and explained 68.56% and 13.2% of the total variance, respectively. Salinity had a score of >0.73 and loaded positively onto PC1, while the other measured traits of plant height, stem diameter, leaf area, fruit yield, and WUE had high scores > 0.88 (Table 10). PC1 had a positive correlation with all measured traits except for nutrient and grafting treatments, which demonstrated a negative correlation with all other traits. The eigenvector's distance and direction characterized the relationships between the traits and the imposed treatments. The scattering of the studied tomato traits in the same direction helped group them by similar physiological traits that were associated with salt tolerance. The PCA demonstrated that WUE had a stronger correlation with salinity treatment than with other parameters, followed by grafting status.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline  & **F1** & **F2** & **F3** & **F4** \\ \hline Eigenvalue & 5.485 & 1.056 & 1.004 & 0.199 \\ Variability (\%) & 68.562 & 13.201 & 12.555 & 2.493 \\ Cumulative \% & 68.562 & 81.763 & 94.318 & 96.810 \\ \hline Salinity & **0.726** & 0.219 & 0.007 & 0.001 \\ Nutrient & 0.029 & 0.025 & **0.943** & 0.000 \\ Grafting & 0.183 & **0.751** & 0.049 & 0.003 \\ Plant height & **0.925** & 0.001 & 0.000 & 0.035 \\ Stem diameter & **0.885** & 0.018 & 0.001 & 0.082 \\ Leaf area & **0.926** & 0.003 & 0.001 & 0.017 \\ Yield & **0.909** & 0.002 & 0.003 & 0.018 \\ WUE & **0.901** & 0.037 & 0.000 & 0.044 \\ \hline \hline \end{tabular} Note: Values \(\geq\) 0.48 are presented in boldface and indicate traits found to be important for salinity tolerance.  
\end{table}
Table 10: Principal component analysis of tomato traits: eigenvalues, proportion, and cumulative variance for the four principal components underlying the effects of salinity stress.  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Season 1**} & \multicolumn{4}{c}{**Season 2**} \\ \cline{2-9}  & \multicolumn{2}{c}{**Chlorophyll**} & \multicolumn{1}{c}{**Ca\({}^{2+}\)**} & \multicolumn{1}{c}{**K\({}^{+}\)**} & \multicolumn{1}{c}{**Na\({}^{+}\)**} & \multicolumn{1}{c}{**Chlorophyll**} & \multicolumn{1}{c}{**Ca\({}^{2+}\)**} & \multicolumn{1}{c}{**K\({}^{+}\)**} & \multicolumn{1}{c}{**Na\({}^{+}\)**} \\ \hline Pr \(>\) F & Salinity (S) & \textless{}0.0001 & \textless{}0.0001 & \textless{}0.0001 & \textless{}0.0001 & \textless{}0.0001 & \textless{}0.0001 & \textless{}0.0001 & \textless{}0.0001 \\  & Nutrient (N) & \textless{}0.0001 & 0.0336 & 0.0014 & 0.0008 & \textless{}0.0001 & 0.0394 & 0.0141 & 0.0008 \\  & Graft (G) & 0.36063 & 0.71442 & 0.79227 & 0.77292 & 0.3446 & 0.6826 & 0.757 & 0.7385 \\  & S\({}^{\text{N}}\) & \textless{}0.0001 & \textless{}0.0001 & \textless{}0.0001 & \textless{}0.0001 & \textless{}0.00394 & 0.0141 & 0.0008 \\  & S\({}^{\text{G}}\) & 0.10926 & 0.43533 & 0.26676 & 0.2817 & 0.1044 & 0.4159 & 0.2549 & 0.2692 \\  & N\({}^{\text{G}}\) & 0.0009 & 0.00729 & 0.00333 & 0.00279 & 0.0008 & 0.0069 & 0.0031 & 0.0027 \\  & S\({}^{\text{N}}\)\({}^{\text{G}}\) & 0.17847 & 0.33777 & 0.459 & 0.38961 & 0.1705 & 0.3227 & 0.4386 & 0.3722 \\ LSD\({}_{0.05}\) & & 0.00252 & 0.01476 & 0.0105 & 0.00918 & 0.0028 & 0.0164 & 0.0117 & 0.0102 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Leaf tissue analysis of interaction of salinity and nutrient recipe treatments with respect to chlorophyll and ion concentrations in tomato plants.