*3.1. Plant Growth and Biomass Production*

In the first year of the experiment, plants grown on one stem showed significant differences in vegetative parameters regarding rootstock type used (Table 1). Plants grafted on Emperador rootstock had highest leaf area, number of leaves, plant height and leaf and shoot dry biomass (DM) compared to self-grafted plants. The irrigation method and interaction between irrigation and graft did not show significant differences.


**Table 1.** Effect of rootstock type and irrigation treatment on tomato vegetative characteristics in the first year of the experiment with plants grown on one stem.

\* DM—dry mass; † Significant differences between treatments (LSD test at *p* ≤ 0.05) are indicated with different letters within columns. ns—non-significant.

In the second year, statistical analyses for vegetative growth are presented in Table 2. Results are presented per stem for two-stemmed grafted plants with plants of one stem. Similar to the first experiment year, most measured traits were significantly affected by rootstock type. Additionally, the leaf number showed differences in irrigation technique applied. Leaf and shoot DM per stem was significantly highest in Emperador and lowest in Attiya. No difference in these traits were found between one-stem Attiya and Maxifort. It can be concluded that Maxifort produces two times more DM per whole plant.


**Table 2.** Effect of rootstock type and irrigation treatment on tomato vegetative characteristics in the second year of the experiment with plants grown on one and two stem.

\* SG—self-grafted plants; DM—dry mass; † significant differences between treatments (LSD test at *p* ≤ 0.05) are indicated with different letters within columns. ns—non-significant.

#### *3.2. Leaf Gas Exchange*

The leaf gas-exchange parameters measured 20 days after initiation of reduced irrigation treatments (DI + PRD) are in Table 3. Stomatal conductance (gs), intercellular CO2 (Ci), transpiration rate (E) and photosynthetic WUE (PWUE) were significantly affected by irrigation rate. The values of gs, Ci and E were highest under FI and lowest under DI treatment, while PWUE had highest value under DI that differed from FI and PRD. In addition, only stomatal conductance differed (*p* ≤ 0.05) between rootstocks, with plants grafted on Emperador having the highest values. The effect of the interaction of the rootstock/plant type × irrigation was recorded for photosynthetic rate (A), photosynthetic WUE (Figure 1A,B) and intercellular CO2 (data not shown). The highest A was measured for one stem self-grafted Attiya under DI, while lowest was found for same plants under FI. On average, PWUE was highest at DI and as shown by interaction did not differed between plant types under DI, while differences in two other irrigation treatments was influenced by rootstock.

**Figure 1.** Photosynthetic rate (**A**,**B**) photosynthetic water-use efficiency—PWUE of grafted tomato plants grown with one or two stems under three irrigation techniques. Vertical bars represent SE values (*n* = 6). a—significant difference by the LSD test at *p* ≤ 0.05 are indicated by different letters above column; ATT—one-stem Attiya; AT—two-stem Attiya; EM—Emperador, MX—Maxifort.


**Table 3.** Leaf gas-exchange parameters and photosynthetic water-use efficiency of grafted tomatoes grown with one and two stems under three irrigation techniques in the second year of the experiment.

\* Significant differences between treatments (LSD test at *p* ≤ 0.05) are indicated with different letters within columns. ns—non-significant.
