Effect of integrated use of recycled wastewater and plant growth-promoting rhizobacteria (PGPR) on the quality characteristics of safflower ( <i>Carthamus tinctorius</i> L.) under deficit irrigation in semi-arid conditions

Abstract This study, conducted under semi-arid conditions during the 2022 and 2023 growing seasons, aimed to assess the effects of plant growth-promoting rhizobacteria (PGPR) in combination with different irrigation levels and water qualities on safflower (Carthamus tinctorius L.) quality parameters. The irrigation levels were based on 0% (I0 - rainfed), 25% (I25), 50% (I50), 75% (I75) and 100% (I100) of Class A pan evaporation. Two irrigation water qualities were used: recycled wastewater (RW) and freshwater (FW). The PGPR treatments were applied at four frequencies: R0 (control), R1 (once), R2 (twice) and R3 (three times) starting after sowing at 10-day intervals. Seed protein content ranged from 12.0% to 18.1%, with the highest values under I100-R3 and the lowest under I0-R0. Protein content increased with irrigation and bacterial application frequency. Oil content varied between 25.2% and 38.6%, peaking under full irrigation with triple PGPR application (I100-R3), and was generally higher in RW-irrigated plots. SPAD (Soil Plant Analysis Development) values which are an indication for chlorophyll content in the plant ranged from 45.1 to 76.3, with RW-I100 treatments showing the highest readings. Stomatal conductance values varied between 40.5 and 122.0 mmol/m 2 /s¹, increasing with irrigation level. Overall, combining recycled wastewater and PGPR under sufficient irrigation significantly improved safflower’s physiological and biochemical characteristics. The results suggest that this integrated approach enhances oil and protein content while supporting sustainable water use and crop quality improvement in arid and semi-arid regions.