## 3 Results
+I: Seed inoculation with the selected PGPB (plant growth-promoting bacteria) consortium (bacterial suspension was also added to ports every 3 weeks); -I: No PGPB inoculation (durum wheat seeds were treated with non-inoculated NB medium before planting); CF: Soil treated with full dose of chemical fertilizer; \(\frac{1}{2}\)CF: Half dose of chemical fertilizer; \(-\)CF: No chemical fertilizer. NPC: Non-photochemical quenching coefficient; qCN: Complete non-photochemical quenching of ChIP; qTV: Total quenching of variable ChIP; qTQ: Total quenching of ChIP; PQ: Ratio of the quantum yield of actual PSII photochemistry in LAS to the quantum yield of the constitutive non-regulatory NPQ; SD: Standard deviation. All the treatments, especially the PGPB inoculations, improved the total quenching of variable ChIF (qTV) and total quenching of ChIF (qTQ) as compared to the control in all experiments. In this regard, the highest rate of qTV observed in I + CF (under non-stress and drought) and I + \(\frac{1}{2}\)CF (in saline condition) which was significantly higher than control treatment up to 3.5, 5.5, and 6%, respectively. However, there was no significant difference among all chemical and inoculums treatments in terms of qTV rate (Table 3). qTQ varied from 0.74 (control) to 0.76 (I, I + CF and I + \(\frac{1}{2}\)CF) in non-stress, 0.71 (control) to 0.75 (I + \(\frac{1}{2}\)CF) in drought, and 0.71 (control) to 0.75 (I + CF and I + \(\frac{1}{2}\)CF) in salinity conditions (Table 3). According to the results in non-stress conditions, all chemical treatments and PGPB inoculums improved up to 13% the ratio of the quantum yield of actual PSII photochemistry in LAS to the quantum yield of the constitutive non-regulatory NPQ (PQ), as compared to the unfertilized (control) treatment. PGPB inoculations combined with half dose of the chemical fertilizer (I + \(\frac{1}{2}\)CF), significantly increased the PQ rate as compared to the control plants under drought and salinity stresses (26 and 27%, respectively), which was non-significantly higher than I + CF and I treatments in drought (14 and 11%, respectively) and I + CF in salinity (4%) conditions (Table 3). Grain yield in all experiments was affected by PGPB inoculation and chemical fertilization. This parameter varied from 0.52 to 1.15 g/plant in non-stress, 0.26 to 0.46 g/plant in drought, and 0.35 to 0.69 g/plant in salinity condition. In this regard, the highest grain yield in non-stressed plants was achieved by I + CF treatment, which was 122, 53, 12, and 9% more than that in control, I, CF, and I + \(\frac{1}{2}\)CF treatments, respectively. Almost the same trend was observed in the saline condition, where the grain yield after treating by I + CF was significantly higher than control (+97%) and half dose of the chemicals (+41%), while it was non-significantly more than I (+13%), CF (+15%), and I + \(\frac{1}{2}\)CF (+25%) treatments. The responses of drought-stressed plants to the microbiological and chemical fertilization treatments were slightly different. Accordingly, the highest grain yield was found by the application of PGPB inoculants (I), which had no statistically significant difference with CF (+17%), I + \(\frac{1}{2}\)CF (+6%), and I + CF (+21%) treatments, while was significantly higher than \(\frac{1}{2}\)CF(+60%) and control (+82%) treatments (Figure 1). Figure 1: Grain yield in response to the chemical/ microbiological fertilization managements under non-stress, salt, and drought conditions. Co: Control (no PGPB (plant growth-promoting bacteria) inoculation and no chemical fertilizer); I: Seed inoculation with the selected PGPB consortium (bacterial suspension was also added to pots every 3 weeks); CF: Soil treated with full dose of chemical fertilizer; CF/2: Half dose of chemical fertilizer; I + CF and I + CF/2: Inoculation and chemical fertilization. Means on the bars marked by the same letter(s) are not significantly different based on the least significant difference (LSD) test at 0.05 probability level.