*3.1. E*ff*ect on Relative Water Content (RWC%)*

The presented results in Figure 1A showed a significant decrease in RWC in sweet pepper under two salinity concentrations (57.6% at the low concentration (34 mM) (S1) and 52% at the high concentration (68 mM) (S2) comparing with control plants (74.6%) as the mean of the two seasons. Likewise, the results in Figure 1 revealed that seed treatment with *B. thuringiensis* showed a significant increase in RWC in stressed plants (65.7% compared with 57.6% at the low concentration and 60.8% compared with 52% at the high concentration). Furthermore, chitosan application at 30 mg dm−<sup>3</sup> caused a significant increase in RWC (71.5% compared with 57.6% at the low concentration of salinity) and (67.1% compared with 52% at the high concentration) as a mean of both seasons in the stressed plants. The best treatment under salinity conditions was chitosan at 30 mg·dm−<sup>3</sup> which achieved 71.5% when compared with control plants 74.6% without any significant difference.

#### *3.2. E*ff*ect on Chlorophyll a and b Concentrations*

It is obvious from the achieved results in Figure 1B–C that chlorophyll was significantly reduced in stressed plants; chlorophyll *a* significantly decreased at low concentration of salinity (2 mg·g−<sup>1</sup> FW<sup>−</sup>1) compared with control (2.85 mg·g−<sup>1</sup> FW<sup>−</sup>1) as the mean of both seasons. Furthermore, the high salinity concentration caused a significant reduction in chlorophyll *a* (1.25 mg·g−<sup>1</sup> FW<sup>−</sup>1) in stressed plants compared to control (2.85 mg·g−<sup>1</sup> FW<sup>−</sup>1). Similarly, salinity stress led to a significant decrease in chlorophyll *b* concentration, the two concentrations caused significant decreases (0.84 and 0.55 mg·g−<sup>1</sup> FW−<sup>1</sup> respectively) compared with control (2.85 mg·g−<sup>1</sup> FW<sup>−</sup>1). Nonetheless, seed treatment with *B. thuringiensis* and chitosan application led to significant increases in chlorophyll *a* and *b*. The greatest result was obtained with chitosan (S1 + Chitosan) treatment (2.85 mg·g−<sup>1</sup> FW<sup>−</sup>1) in the stressed plants with the low salinity concentration compared to the stressed plants (S1) without treatments (2 mg·g−<sup>1</sup> FW<sup>−</sup>1).

#### *3.3. E*ff*ect on Electrolyte Leakage (EL%)*

The presented data in Figure 1D exhibited that EL% significantly increased in the stressed plants, the low salinity concentration caused significant increase (42.3%) comparing with control (13.8%) as the mean of two seasons. Furthermore, the high salinity concentration was more harmfully effective and caused a significant increase in EL% (52.6%) compared with control (13.8%). Nevertheless, chitosan application 30 mg dm−<sup>3</sup> and seed treatment with *B. thuringiensis* led to significant decrease in EL% in the stressed plants under the two concentrations. Seed treatment with *B. thuringiensis* caused a positive effect and significant decrease in EL% (30.2% and 37.6%) in the stressed plants at the two concentrations compared with untreated plants (42.3% and 52.6%), respectively. Furthermore, EL% was reduced significantly in the stressed treated plants with chitosan 30 mg dm−<sup>3</sup> (21.7% and 27.2%) that compared with the stressed untreated plants (42.3% and 52.6%).

**Figure 1.** Effect of *B. thuringiensis* and chitosan on relative water content (**A**) chlorophyll *a*, (**B**) chlorophyll *b*, (**C**) and electrolyte leakage (**D**) under two salinity concentrations in sweet pepper plants during two seasons [first season (2019) and second season (2020)]. Data is the mean (±SE) of four replicates. Different letters above the data columns indicate significant differences between the samples determined by ANOVA, Duncan's multiple range test at 0.05 level.

#### *3.4. E*ff*ect on Proline Concentration*

It could be noted from Figure 2A that the exposed plants to salinity at (S1) and (S2) caused a significant increase in proline concentration, the high concentration of salinity (S2) achieved the high concentration of proline (24 μg·g−<sup>1</sup> FW) comparing to control (9.1 μg·g−<sup>1</sup> FW) as the mean of both seasons in sweet pepper. Application of seed treatment with *B. thuringiensis* and chitosan application in stressed plants led to regulate proline accumulation when compared with the control and the stressed untreated plants. *B. thuringiensis* seed treatment led to the regulation of proline accumulation in the stressed plants (12.7 μg·g−<sup>1</sup> FW at the low concentration of salinity and 13.6 μg·g−<sup>1</sup> FW at the high concentration comparing to the stressed untreated plants 17.4 and 24 μg·g−<sup>1</sup> FW) at the two concentrations, respectively. Chitosan application had a significant effect on proline content (9.8 and 12.2 μg·g−<sup>1</sup> FW) compared with stressed untreated plants (17.4 and 24 μg·g−<sup>1</sup> FW) at the two concentrations, respectively. The difference was not significant between the both seasons.

**Figure 2.** Effect of *B. thuringiensis* and chitosan on proline content (**A**) and maximum efficiency of PSII (*Fv*/*Fm*) (**B**) under two salinity concentrations in sweet pepper during two seasons. Data is the mean (±SE) of four replicates. Different letters above the data columns indicate significant differences between the samples determined by ANOVA, Duncan´s multiple range test at 0.05 level.

#### *3.5. E*ff*ect on Chlorophyll Fluorescence Parameter (Fv*/*Fm)*

Our results in Figure 2B indicated that chlorophyll fluorescence parameters were adversely affected under salinity conditions. The maximum efficiency of PSII (*Fv*/*Fm*) significantly reduced in sweet pepper (0.790) at the low salinity concentration and (0.729) at the high salinity concentration, respectively comparing to the control (0.822). However, seed treatment with *B. thuringiensis* caused significant increase in *Fv*/*Fm* ratio in the stressed plants (0.791) at the low concentration of salinity and (0.769) at the high salinity concentration when compared with the stressed untreated plants (0.790) at the low concentration and (0.729) at the high salinity concentration. Likewise, under the two concentrations, chitosan caused a significant increase in *Fv*/*Fm* ratio. The best treatment was chitosan at the low salinity concentration (0.815) compared with control (0.822).

#### *3.6. E*ff*ect on Lipid Peroxidation as Malondialdehyde*

According to the findings in Figure 3, lipid peroxidation (MDA) significantly increased in sweet pepper (11.35 and 13.8 μmol·g−<sup>1</sup> FW) at the two salinity concentrations, respectively as the mean of both seasons when compared with control plants (6.75 μmol·g−<sup>1</sup> FW). Nevertheless, MDA significantly decreased in the stressed plants according to seed treatment with *B. thuringiensis* and chitosan treatment. *B. thuringiensis* treatment had a positive effect on MDA and led to significant reduction in the MDA content at the two salinity concentrations (8.8 and 10.5 μmol·g−<sup>1</sup> FW) when compared with the stressed untreated plants (11.35 and 13.8 μmol·g−<sup>1</sup> FW). The application of chitosan significantly reduced MDA content in sweet pepper under the two salinity concentrations (7 and 7.85 μmol·g−<sup>1</sup> FW) when compared with stressed untreated plants (11.35 and 13.8).

**Figure 3.** Effect of *B. thuringiensis* and chitosan on lipid peroxidation (**A**), H2O2 (**B**) and O2 <sup>−</sup> (**C**) under two salinity concentrations in sweet pepper during two seasons. Data is the mean (±SE) of four replicates. Different letters above the data columns indicate significant differences between the samples determined by ANOVA, Duncan´s multiple range test at 0.05 level.

#### *3.7. E*ff*ect on O2* <sup>−</sup> *and H2O2*

ROS, mainly O2 <sup>−</sup> and H2O2 significantly increased under the both salinity concentrations (Figure 3). O2 <sup>−</sup> significantly increased (47.4 and 63 units) at the two salinity concentrations compared with control (24.16 units). Conversely, *B. thuringiensis* treatment caused a significant decrease in O2 <sup>−</sup> in the salt stressed plants (38.3 and 52.3 units) in comparison with stressed untreated plants (47.4 and 63 units). Also, chitosan treatment caused a significant decrease in O2 <sup>−</sup> (31.7 and 48.3 units) when compared with the stressed untreated plants (47.4 and 63 units).

Salinity stress caused a significant increase in H2O2 in sweet pepper (16 and 18.1 units) at the two concentrations, respectively as compared to control (10.3 units). However, the levels of H2O2 were decreased significantly according to *B. thuringiensis* seed treatment and chitosan application in the stressed plants at the two salinity concentrations. Chitosan application gave the best and most significant results (10.3 and 11.8 units) compared to stressed untreated plants (16 and 18.1 units) at the two salinity concentrations, respectively.

### *3.8. E*ff*ect on the Activity of Catalase (CAT), Peroxidase Activity (POX), Superoxide Dismutase (SOD) and Glutathione Reductase (GR) Enzymes*

Salinity stress at both concentrations caused significant increases in CAT, POX, SOD and GR enzyme (Figure 4). CAT activity significantly increased in the stressed plants (124.8 and 149.3 mM H2O2 g−<sup>1</sup> FW min<sup>−</sup>1) at the two salinity concentrations, respectively, when compared with control (78.6 mM H2O2 <sup>g</sup>−<sup>1</sup> FW min<sup>−</sup>1).

However, chitosan treatment and *B. thuringiensis* seed treatment caused significant reduction in CAT activity at both salinity concentrations. Chitosan with the low salinity concentration (S1 + Chitosan) gave the best result (85.8 mM H2O2 <sup>g</sup>−<sup>1</sup> FW min<sup>−</sup>1) as compared to stressed untreated plants (124.8 mM H2O2 g−<sup>1</sup> FW min<sup>−</sup>1) and control plants (78.6 mM H2O2 g−<sup>1</sup> FW min<sup>−</sup>1). Moreover, POX, SOD and GR activities significantly increased in the stressed plants at the low salinity concentration (0.6 μmol tetra-gualacol g−<sup>1</sup> FW min<sup>−</sup>1, 74.5 and 0.59 unit/cm3) as compared to control plants (0.24, 38.3 and 0.36), also, the enzymes activity significantly increased in the stressed plants at the high concentration (0.76, 98.7 unit mg−<sup>1</sup> FW min−<sup>1</sup> and 0.59 unit/cm3) respectively. Nevertheless, chitosan application and seed treatment with *B. thuringiensis* caused a significant reduction in POX, SOD, and GR activity in the stressed plants at the two salinity concentrations compared to the stressed untreated plants.

**Figure 4.** *Cont.*

**Figure 4.** Effect of *B. thuringiensis* and chitosan on the activity of CAT (**A**), POX (**B**), SOD (**C**) and GR (**D**) under two salinity concentrations in sweet pepper during two seasons. Data is the mean (±SE) of four replicates. Different letters above the data columns indicate significant differences between the samples determined by ANOVA, Duncan´s multiple range test at 0.05 level.
