Impaginato 129 Adv. Hort. Sci., 2024 38(2): 129­139 DOI: 10.36253/ahsc­15671 Salicylic acid and iron­oxide nano­ particles improved the growth and productivity of ajowan under salt stress K. Ghassemi­Golezani (*), S. Abdoli Department of Plant Ecophysiology, Faculty of Agriculture, University of Tabriz, Tabriz, Iran. Key words: Foliar application, root growth, salinity, seed filling, yield parameters. Abstract: Two factorial experiments with randomized complete block design in three replicates were conducted in a greenhouse at the University of Tabriz to investigate the individual and combined effects of SA and Fe2O3­NPs spray (1 mM and 3 mM, respectively) on cations contents, root and shoot growth, seed filling and yield parameters of salt­stressed ajowan plants (0, 4, 8 and 12 dS m­1 NaCl; as non­saline and low, moderate and high salinities, respectively). Salt stress enhanced Na+ contents and reduced K+ and Ca2+ contents, and K+/Na+ and Ca2+/Na+ ratios, leading to a reduction in root and shoot growth, particularly under high salinity. Reduction in plant growth parameters under salt stress had a negative impact on yield components and seed yield of ajowan. These deleterious impacts of salinity on plants were largely overcome by foliar treatments, particularly by SA + Fe2O3­NPs. The improvement of seed yield by these treatments was highly correlated with enhanced root and shoot growth, seeds per plant, and 1000­seed weight, especially under moderate and high salinities. Thus, the simultaneous application of SA and Fe2O3­NPs was the best foliar treatment for enhancing the growth and productivity of ajowan plants under normal and saline conditions. 1. Introduction Growth and development of plants are constantly influenced by various environmental stresses including salinity (Sarker and Oba, 2019). Salt stress triggers many cellular events, causing physiological, biochemical and eventually morphological alterations. This stress chiefly causes ionic toxicity by enhancing Na+ concentration in plant cells, which ultimately prevents the acquisition of essential nutrients, ionic homeostasis and cell metabolism (Nikpour­Rashidabad et al., 2022). Salinity not only causes cellular water imbalance, osmotic stress and abscission, but also significantly influences different photosynthetic enzymes and gas exchange parameters (Lotfi et al., 2020; Rasheed et al., 2020). Salt toxicity may also lead to oxidative stress due to the physiological imbalance between the generation and scavenging of (*) Corresponding author: golezani@gmail.com Citation: GHASSEMI­GOLEZANI K., ABDOLI S., 2024 ­ Salicylic acid and iron‐oxide nanoparticles impro‐ ved the growth and productivity of ajowan under salt stress. ­ Adv. Hort. Sci., 38(2): 129­139. Copyright: © 2024 Ghassemi­Golezani K., Abdoli S. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The authors declare no competing interests. Received for publication 9 January 2024 Accepted for publication 10 March 2024 AHS Advances in Horticultural Science https://doi.org/10.36253/ahsc-15671 http://www.fupress.net/index.php/ahs/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2024 38(2): 129­139 130 reactive oxygen species (ROS) (Ghassemi­Golezani and Abdoli, 2022 a). Elevated ROS may cause the oxidation of proteins and membrane lipids and also impair cellular redox homeostasis. A stress­induced decline in plant growth and productivity is a common phenomenon in many plant species, which is most likely attributed to the changes in plant physiology, and metabolism (Ghassemi­Golezani et al., 2021; Ghassemi­Golezani and Rahimzadeh, 2022) and phenology attributes (Kazan and Lyons, 2016). The major negative impacts of salinity on root growth have been formerly confirmed in Portulaca oleracea (Kafi and Rahimi, 2011), Mentha spicata (Chrysargyris et al., 2019), Oryza sativa (Chang et al., 2019) and Jatropha curcas (Abrar et al., 2020), Brassica napus (Ghassemi­Golezani and Abdoli, 2022 b) plants. Therefore, salt toxicity is an escalating problem in different agricultural systems worldwide. The emerging roles of plant hormones and nanoparticles in modulating various abiotic stresses have been extensively evaluated (Ghassemi­Golezani and Abdoli, 2021; Singh et al., 2021 b). Salicylic acid (SA) as a naturally phenolic hormone has effectual roles in numerous metabolic processes and regulates photosynthesis and antioxidant activities, redox and osmotic hemostasis, ionic uptake and secondary metabolite synthesis in plants exposed to salinity (Abdoli and Ghassemi­Golezani, 2021; Hussain et al., 2021). Salicylic acid can reverse the ethylene­induced detrimental impacts via modulating the transcription of ACS, NHX, sos1, HKT1 and HKT2 genes, and improving antioxidants capacity, leading to an increase in shoot and root growth, leaves per plant, leaf area and plant productivity (Rao et al., 2021). Simultaneous application of SA and nanoparticles can be more effective in augmenting the ameliorative effects of SA under salt stress (Mozafari et al., 2018; Ghassemi­Golezani and Abdoli, 2021). Nanoparticles (NPs) rapidly penetrate the plant cell due to their small size and high solubility, thereby compensating the nutrient deficiencies. Through phloem vessels and plasmodesmata, foliar applied nanoparticles can be transferred into the cells (Knoblauch and Oparka, 2012). The bond between carrier proteins and nanoparticles facilitates the entry of nanoparticles into the cells through ion channels, aquaporin, and endocytosis (Nair et al., 2010). Since the uptake of most micronutrients is reduced under salinity, supplying nano­forms of these elements not only reduces nutritional imbalance, but also helps the plants to cope with stress through various physiological and metabolic changes. For instance, silica NPs boost salt tolerance by regulating ion homeostasis, osmotic adjustment and chlorophyll content, which recover plant growth and productivity (Alsaeedi et al., 2019). Iron oxide NPs may have critical roles in different biochemical synthesis, antioxidant activity and genes expression (Moradbeygi et al., 2020). The Fe2O3­NPs induced salt tolerance in Moldavian balm plants was due to augmenting DPPH radical scavenging activity, biochemical compounds accumulation and stimulating expression of genes involved in the bio­ synthesis pathway of important phenolic acids such as rosmarinic acid (Moradbeygi et al., 2020). Recent investigations indicated that foliar spray of Fe2O3­NPs on plants under salt stress notably increased chlorophyll concentration, carbohydrate content (i.e., sugars), and enzymatic defense capacity. Moreover, it decreased lipid peroxidation and ROS generation (Singh et al., 2021 a). According to Dola et al. (2022) application of 200 ppm iron­oxide nanoparticles resulted in an improvement of plant growth, relative water content chlorophyll content, 100­seed weight, seed yield, and protein and oil contents of soybean. Adding Fe2O3­NPs to the soil enhanced leaf area, leaf number per plant, shoot length, and shoot and root weights of tomatoes (El­ Desouky et al., 2021). Improving plant growth by iron oxide nanoparticles was also observed by several studies on wheat (Rizwan et al., 2019; Manzoor et al., 2021; El­Saber et al., 2021). Ajowan (Trachyspermum ammi L.) is a medicinal plant belonging to the Apiaceae family.It is well known for its essential oil (up to 5%), particularly in seeds (Minija and Thoppil, 2002). Due to numerous pharmacological properties of ajowan essential oil including stimulant, antiseptic, anesthetic, antimicrobial, antiviral, antiulcer, antihypertensive, antitussive, antihyperlipidemic and bronchodilatory, this plant is widely employed (Bhadra, 2020). In our previous reports (Abdoli et al., 2020; Ghassemi­ Golezani and Abdoli, 2021) the mechanisms of improving salt tolerance in ajowan plants by salicylic acid and iron oxide nanoparticles were discussed in details. In addition to the reported results, this research aimed at evaluating the growth responses of ajowan to these treatments focusing on root and shoot growth, and yield­related traits under salt stress. Ghassemi‐Golezani and Abdoli ‐ Improving ajowan performance by foliar treatments 131 2. Materials and Methods Experimental conditions and treatments Two pot experiments with a factorial arrangement based on a randomized complete block design in three replicates were set up in a greenhouse at the University of Tabriz, Iran, to investigate the effects of individual and simultaneous application of SA (1 mM) and Fe2O3­NPs (3 mM) on sodium, potassium and calcium contents, root and shoot growth, seed filling and yield parameters of salt­stressed (0, 4, 8 and 12 dS m­1 NaCl; as non­saline and low, moderate and high salinities, respectively) ajowan plants. The salinity (Nikpour­Rashidabad et al., 2022) and foliar spray (Hussain et al., 2019; Ghassemi­Golezani and Farhadi, 2022) levels were selected according to previous reports. The average temperatures of day and night, relative humidity and light intensity in the greenhouse were 29°C, 25°C, 35­40%, and 141 Wm­2 (about 780 µmol m­2s­1), respectively. This research was performed with 52 pots (48 pots for sowing and 4 unsown pots for checking the water status). Ajowan seeds (30 seeds per pot) were sown in each pot in 1 cm depth of a mixture of perlite and cocopeat to keep long­term moisture in the substrate. The tested salt solutions were added to the substrate of the pots up to 100% field capacity (FC). The emerged seedlings were reduced to keep 10 plants per pot. The water loss from the pots was compensated by tap water or Hoagland solution (EC=1.3 dS m­1, pH=6.7­7.2) up to 100% FC. Toprevent excess increment of EC in the substrate due to Hoagland addition, the perlite + cocopeat within all pots were washed slowly every 30 days by pouring water into the pots and draining from the lower holes of the pots. The EC of draining water was measured frequently and when the pouring and draining waters showed similar ECs, washing was stopped and then re­treated with salt solutions. The SA, Fe2O3­NPs and tap water were sprayed on plants at two different stages (7 leaves and flowering), by a two­liter manual sprayer. Estimation of Na+, K+ and Ca2+ contents The sodium, potassium and calcium contents in plant tissues were determined by a flame photometer (Corning flame photometer, 410). The samples of ajowan plants were reduced to dry ashes in an electric furnace at 500℃ for 7 h, and the carbon­free residue was then dissolved in 1 N HCl. The Na+, K+ and Ca2+ contents were determined as milligrams per gram dry weight. Measurement of root and shoot parameters Two plants from each pot were removed at maturity. The roots were cut from the crown and thoroughly washed and air­dried. Then, the root and shoot lengths, root diameter, branches per plant and leaves per plant were recorded. Subsequently, the samples of roots and shoots were separately dried at 75℃ for 48 h and weighed. Seed filling During seed filling in 2018, two plants from each pot were harvested at 10 days intervals, beginning 20 days after flowering and then seeds were removed from the plants and weighed at five stages. Yield parameters The seeds of two plants from each pot were separated and then the number of umbels per plant, seeds per umbel, seeds per plant, 1000­seed weight and seed yield were determined. The harvest index was calculated as: Harvest index = (Seed yield/shoot + seed mass) × 100 Statistical analysis All collected data in this study were subjected to a two­way analysis of variance (ANOVA) using MSTAT­ C, and means were compared by Duncan ̓ s multiple range test at p ≤ 0.05. The mean data were presented as means ± standard error. Pearson correlation coefficient was used to analyze the relations between morphological and yield­related traits of ajowan plants, using SPSS 16. 3. Results The Na+, K+ and Ca2+ contents The Na+, K+ and Ca2+ contents and K+/Na+ and Ca2+/Na+ ratios were significantly affected by salt stress and foliar treatments (p ≤ 0.01). The K+ and Ca2+ contents and K+/Na+ and Ca2+/Na+ ratios were decreased, while the Na+ content was increased by the increment of salt toxicity. The 4 dS m­1 NaCl had no significant impact on Ca2+ content. Foliar treatments, particularly SA + Fe2O3­NPs, reduced Na+ content and enhanced K+ and Ca2+ contents and K+/Na+ and Ca2+/Na+ ratios. Differences between SA and SA + Fe2O3­NPs treatments in Na+ and Ca2+ Adv. Hort. Sci., 2024 38(2): 129­139 132 contents and Ca2+/Na+ ratio were not statistically significant. All of these parameters (except K+/Na+ ratio) were similarly affected by SA and Fe2O3­NPs treatments (Table 1). Root growth Significant interaction of salt stress and foliar treatments were observed for root growth parameters (p≤0.01). The length, weight and diameter of ajowan roots were decreased as salinity increased. No differences among foliar treatments in root parameters were recorded under low salinity. Nonetheless, foliar sprays significantly promoted root growth of plants at different saline conditions, especially under moderate and high salinities. The SA and SA + Fe2O3­NPs treatments were the superior treatments in improving root growth (Table 2). In most cases, the differences betweenhormonal and nutritional treatments were not statistically significant (Table 2). Shoot parameters A significant interaction of salinity and foliar applications was observed for shoot mass and length, branches and leaves per plant (Table 3). Increasing salinity significantly decreased shoot parameters. The shoot length of treated and untreated plants was not significantly varied under non­saline conditions. However, foliar treatments significantly increased shoot length under all salinity levels. The shoot mass, and branches and leaves per plant were enhanced by different foliar treatments, especially by SA + Fe2O3­ NPs, under saline and non­saline conditions. The differences among SA, Fe2O3­NPs and SA + Fe2O3­NPs treatments in shoot mass under 4 dS m­1NaCl, in shoot length under 4 and 8 dS m­1 NaCl and in branches per plant under 8 dS m­1 NaCl were not significant (Table 3). Seed filling The dry weight of ajowan seeds was gradually enhanced with seed development up to about 50 days after flowering and afterwards no significant changes occurred. Seed dry weight was not significantly affected by low salinity (4 dS m­1 NaCl), but further increment of salt stress, particularly high salinity, caused a significant decrease in the dry weight of ajowan seeds at later stages of seed development under all foliar treatments. Application of SA, Fe2O3­NPs individually and in combination form increased seed weight under moderate and high salinities. This improvement was mainly due to increasing seed filling rate rather than seed filling duration (Fig. 1). Yield components The interaction of salinity and foliar treatments was significant for umbels per plant, seeds per plant, 1000­seed weight, seed yield and harvest index (Table 4). Seeds per umbel were only affected by salt stress. Low salinity had no significant effect on seeds per umbel. However, further increment in salinity Table 1 ­ The Na+, K+ and Ca2 + contents (mg g­1 dry weight) of ajowan plants affected by foliar treatments under saline and non­saline conditions Different letters in each column indicate significant differences at p≤0.05; ** = significant at p≤0.01. Fe2O3­NPs= Iron­oxide nanoparticles; SA= Salicylic acid. Treatments Na+ K+ Ca2+ K+/Na+ Ca2+/Na+ Salinity conditions Non­Saline 9.29 ± 0.45 d 45.17 ± 1.8 a 13.94 ± 0.24 a 5.05 ± 0.38 a 1.53 ± 0.06 a 4 dS m­1 NaCl 15.14 ± 1.17 c 40.86 ± 1.8 b 13.19 ± 0.43 a 2.86 ± 0.23 b 0.92 ± 0.08 b 8 dS m­1 NaCl 27.57 ± 0.99 b 30.72 ± 1.3 c 10.63 ± 0.55 b 1.15 ± 0.08 c 0.40 ± 0.03 c 12 dS m­1 NaCl 32.35 ± 1.51 a 28.01 ± 1.2 d 7.82 ± 0.72 c 0.90 ± 0.07 d 0.25 ± 0.03 d F test 479.64 ** 220.88 ** 60.57 ** 679.22 ** 369.80 ** Foliar treatment Water 26.39 ± 3.52 a 28.36 ± 1.74 c 9.91 ± 1.19 c 1.53 ± 0.33 d 0.57 ± 0.14 c SA 19.53 ± 2.72 b 37.97 ± 2.49 b 11.86 ± 0.64 ab 2.82 ± 0.61 b 0.86 ± 0.17 ab Fe2O3­NPs 19.30 ± 2.47 b 37.16 ± 2.22 b 11.23 ± 0.81 b 2.56 ± 0.46 c 0.78 ± 0.15 b SA+Fe2O3­NPs 19.14 ± 2.60 b 41.28 ± 2.29 a 12.58 ± 0.58 a 3.04 ± 0.63 a 0.89 ± 0.16 a F test 52.44 ** 101.29 ** 10.15 ** 82.99 ** 22.85 ** Ghassemi‐Golezani and Abdoli ‐ Improving ajowan performance by foliar treatments 133 considerably reduced this parameter. The plants grown under high salinity had the lowest seeds per umbel compared to unstressed plants (Fig. 2). Rising salinity significantly reduced the other yield parameters and harvest index. Foliar treatments had no significant effects on 1000­seed weight under non­saline conditionsand on umbels per plant, seeds per plant and harvest index under non­saline and low salinity. However, hormonal and nutritional treatments enhanced these parameters under saline conditions. This improvement was more evident under moderate and high salinities. In these levels of salinities, the SA and SA + Fe2O3­NPs were the best treatments for improving yield parameters, followed by Fe2O3­NPs (Table 4). Correlations All morphological and yield parameters of ajowan had asignificant positive correlation with each other (Table 5). Root and shoot masses and lengths were highly related toeach other and with leaves per plant (r≥0.85**). The root and shoot parameters as well as yield components and harvest index were positively and significantly correlated with seed yield per plant. However, the highest relations with seed yield were recorded for shoot mass and seeds per plant, followed by shoot and root lengths, leaves per plant and 1000­seed weight (Table 5). 4. Discussion and Conclusions The Na+ toxicity negatively influenced different aspects of plant growth such as root and shoot parameters, resulting in less seed production. The salt­treatedajowan plants responded to foliar applications, particularly to SA and SA + Fe2O3­NPs treatments, as demonstrated by higher K+ and Ca2+ Table 2 ­ Combined analysis of variance of the data for root growth parameters of ajowan affected by foliar treatments under saline and non­saline conditions in 2018 and 2019 Different letters in each column indicate significant differences at p≤0.05; NS, *, **= No significant and significant at p≤0.05 and p≤0.01, respectively. Fe2O3­NPs= Iron­oxide nanoparticles; SA= Salicylic acid. Salinity Foliar treatments Root mass (g) Root length (cm) Root diameter (mm) Non­Saline Water 1.88 ± 0.02 abc 32.98 ± 0.05 abc 2.63 ± 0.17 a SA 1.97 ± 0.04 a 34.28 ± 0.6 ab 2.51 ± 0.11 a Fe2O3­NPs 1.94 ± 0.05 ab 34.48 ± 0.5 a 2.37 ± 0.11 ab SA+ Fe2O3­NPs 1.99 ± 0.05 a 34.23 ± 0.4 ab 2.57 ± 0.12a 4 dS m­1 NaCl Water 1.74 ± 0.05 ef 28.95 ± 0.6 d 2.41 ± 0.08 ab SA 1.85 ± 0.03 bcd 32.95 ± 0.5 abc 2.43 ± 0.08 ab Fe2O3­NPs 1.83 ± 0.04 cde 31.83 ± 0.8 c 2.38 ± 0.7 ab SA+ Fe2O3­NPs 1.90 ± 0.04 abc 32.20 ± 0.8 bc 2.48 ± 0.08 a 8 dS m­1 NaCl Water 1.23 ± 0.05 h 17.12 ± 0.7 hi 1.88 ± 0.06 def SA 1.76 ± 0.02 de 24.02 ± 0.8 ef 2.13 ± 0.06 bcd Fe2O3­NPs 1.64 ± 0.03 f 22.47 ± 0.8 f 2.31 ± 0.05 abc SA+ Fe2O3­NPs 1.80 ± 0.03 cde 25.75 ± 1.0 e 2.32 ± 0.10 abc 12 dS m­1 NaCl Water 0.83 ± 0.06 i 14.37 ± 0.6 j 1.62 ± 0.06 f SA 1.50 ± 0.04 g 19.03 ± 0.4 gh 2.05 ± 0.07 cd Fe2O3­NPs 1.21 ± 0.06 h 16.48 ± 0.5 i 1.72 ± 0.09 ef SA+ Fe2O3­NPs 1.48 ± 0.02 g 19.90 ± 0.6 g 2.00 ± 0.06 de Source of variation Year (Y) NS NS NS Salinity (S) ** ** ** Foliar treatments (F) ** ** * Y x S * * NS Y x F NS NS NS S x F ** ** * Y x SxF NS NS NS F test 17.14** 4.39** 2.36* 134 Adv. Hort. Sci., 2024 38(2): 129­139 contents in plant tissues, root and shoot growth and yield­related traits. A high concentration of Na+ ions in the substrate led to an increase in Na+ uptake and accumulation in plant tissues and a decline in K+ and Ca2+ uptake, and K+/Na+ and Ca2+/Na+ ratios (Table 1). This imbalance in the nutrient status of tissues might be due to an injury in the cell membrane and specific ion channels (Jayakannan et al., 2013). However, the reduction of Na+ accumulation by foliar spray, particularly by SA + Fe2O3­NPs, enhanced the uptake of essential nutrients. This improvement could be related to the activation of H+­ATPase and H+­PPase pumps by SA and Fe2O3­NPs treatments that induces Na+ secretion in vacuoles (Ghassemi­Golezani and Abdoli, 2021) and helps plants cope withsalt toxicity.Our results suggest that the enhancement of root growth by these treatments (Table 2) is effective in improving nutrient availability to the plants.The manganese­iron nanoparticles have been reported to increase the efflux of H+ and influx of K+, leading to high K+/Na+ ratio (Wang et al., 2022). The roots play an imperative part in plant establishment in the soil and water and nutrient absorptions. A comprehensive understanding of root response to the foliar spray of SA and Fe2O3­NPs can more likely provide useful information for improving Table 3 ­ Combined analysis of variance of the data for shoot mass, shoot length, brunches and leaves of ajowan plants affected by foli­ ar treatments under saline and non­saline conditions in 2018 and 2019 Salinity Foliar treatments Shoot mass (g) Shoot length (cm) Branches per plant Leaves per plant Non­Saline Water 15.48 ± 0.18 b 99.87 ± 0.72 abc 11.85 ± 0.74 d 58.47 ± 1.10 ab SA 16.08 ± 0.20 a 101.1 ± 0.78 ab 13.82 ± 0.29 ab 57.33 ± 0.88 b Fe2O3­NPs 15.97 ± 0.22 a 99.93 ± 0.70 abc 12.33 ± 0.48 cd 59.10 ± 0.53 ab SA+Fe2O3­NPs 16.17 ± 0.22 a 101.7 ± 0.96 a 14.62 ± 0.44 a 60.78 ± 0.91 a 4 dS m­1 NaCl Water 14.22 ± 0.15 d 95.22 ± 0.70 e 10.50 ± 0.36 e 45.00 ± 0.86 de SA 14.73 ± 0.22 c 96.93 ± 0.99 de 13.40 ± 0.43 bc 51.33 ± 0.95 c Fe2O3­NPs 14.70 ± 0.20 c 99.03 ± 0.64 bcd 12.40 ± 0.34 cd 47.10 ± 0.80 d SA+Fe2O3­NPs 14.90 ± 0.21 c 97.78 ± 0.61 cd 14.17 ± 0.37 ab 50.77 ± 0.68 c 8 dS m­1 NaCl Water 8.63 ± 0.27 g 68.67 ± 0.71 gh 8.85 ± 0.31 fg 31.67 ± 0.80 i SA 12.42 ± 0.27 e 79.22 ± 0.67 f 11.72 ± 0.37 d 41.57 ± 0.69 fg Fe2O3­NPs 11.35 ± 0.34 f 78.82 ± 0.66 f 11.75 ± 0.45 d 39.47 ± 0.46 g SA+Fe2O3­NPs 12.49 ± 0.25 e 80.87 ± 0.68 f 11.67 ± 0.37 d 42.67 ± 0.56 ef 12 dS m­1 NaCl Water 4.52 ± 0.27 j 61.23 ± 0.61 i 8.17 ± 0.42 g 24.00 ± 0.89 j SA 7.54 ± 0.12 h 69.03 ± 0.79 g 9.05 ± 0.28 fg 35.33 ± 0.84 h Fe2O3­NPs 6.25 ± 0.23 i 66.27 ± 0.60 h 8.48 ± 0.38 g 30.70 ± 0.63 i SA+Fe2O3­NPs 7.73 ± 0.09 h 68.80 ± 0.98 g 9.72 ± 0.33 ef 34.67 ± 0.92 h Source of variation Year (Y) NS NS * ns Salinity (S) ** ** ** ** Foliar treatments (F) ** ** ** ** Y ´ S NS NS * NS Y ´ F NS NS NS NS S ´ F ** ** ** ** Y ´ S ´ F NS NS NS NS F test 21.99** 11.64** 3.05** 7.81** Different letters in each column indicate significant differences at p≤0.05; NS, *, **= No significant and significant at p≤0.05 and p≤0.01, respectively. Fe2O3­NPs= Iron­oxide nanoparticles; SA= Salicylic acid. Ghassemi‐Golezani and Abdoli ‐ Improving ajowan performance by foliar treatments 135 crop productivity in saline soils. The length, mass and diameter of roots in salt­stressed plants, especially under moderate and high salinities, were limited due to nutritional (Table 1) and hormonal imbalances (Zhang et al., 2018), that limit cell elongation and division (Yang et al., 2019). The GiA Roots analysis alsorevealed a decrease in the penetration and distribution of plant roots under different levels of salinities, particularly under high saline conditions (Ghassemi­Golezani and Abdoli, 2022 b). These negative impacts of salinity on root growth were relieved by foliar treatments of SA and Fe2O3­NPs (Table 2). The cross­talk of SA with auxins, cytokinins and gibberellins (Shakirova et al., 2003; Agami and Mohamed, 2013; Miura et al., 2013) can potentially promote cell elongation and division. In addition, the expression of auxin biosynthesis genes might be regulated by Fe status of cells (Sun et al., 2017). Iron­ NPs may enhance root growth by inducing OH radical generation and demolition of cell wall polysaccharides (Kim et al., 2014). Stimulation of SA synthesis in plants by Fe2O3­NPs related treatments (Abdoli et al., 2020) is also effective in improving plant growth. Reduction in shoot mass and length, and branches and leaves per plant due to salinity (Table 3) is related to Na+ toxicity and competition of plants for nutrients (Table 1) and water (Abdoli et al., 2020). This is a mechanism for minimizing energy losses and maintaining plant survival chance under stress conditions. It has been confirmed that salt stress leads to growth reduction, which is more pronounced in leaf area (Acosta­Motos et al., 2015), branches and leaves per plant and shoot length and mass (Table 3). Foliar treatments promoted shoot growth by enhancing root growth (Table 2), and improving K+ and Ca2+ contents in plant tissues bylimiting Na+ absorption by the plants (Table 1). The effectiveness of salicylic acid inpromoting cell division and enlargement is also supported by a previous report on wheat plants (Agami and Mohamed, 2013). Inhibition of ethylene synthesis by SA (Khan et al., 2014) can enhance the plant growth duration. A decline in abscisic acid contentdue to iron nanoparticlesmay also promote growth and retard the senescence of plants (Rui et al., 2016). Moreover, iron nanoparticlesareinvolved in protein synthesis and enzymes activation, which can promote the plant growth and reduce the senescence especially under stressful conditions (Sheykhbaglou et al., 2018). Wang et al. (2022) suggested that cytokinin level, SCFTIR1/AFB‐AUX/IAA signaling pathway, ATP synthesis, cell elongation and plant biomass could be enhanced by iron nanoparticles. Decreasing root­ and shoot­related traits (Tables 2 and 3) due to salt stress reduced yield parameters including seed filling rate (Fig. 1), seeds per plant, 1000­seed weight and seed yield (Table 4; Fig. 2). These reductions are most likely attributed to the enhanced vegetative and reduced reproductive periods under salinity (Ghassemi­Golezani and Farhangi­Abriz, 2021). Retarding flowering due to salinity reduced umbels and seeds per plant, 1000­ seed weight, and consequently seed yield (Table 4). The reduction in photosynthetic efficiency (Ghassemi­Golezani et al., 2021) and allocation of assimilates to the seeds (Kafi et al., 2013) might be the main reasons for yield losses under moderate and high salinities. The SA + Fe2O3­NPs treatment alleviated these detrimental impacts of salinity on plant productivity through the improvement of nutrient availability (Table 1), root (Table 2) and shoot (Table 3) growth, photosynthetic potential (Ghassemi­Golezani and Farhadi, 2022) and stimulation of flower­inducing factor (Hayat et al., 2007). In a study on salt­stressed pennyroyal plants, the SA application enhanced Rubisco activity, a Fig. 1 ­ Changes in mean seed weight during seed development in response to salinity and foliar treatments. Fe2O3­NPs= Iron oxide nanoparticles, SA= Salicylic acid. Adv. Hort. Sci., 2024 38(2): 129­139 136 critical enzyme in photosynthetic machinery.The enhanced seed­filling rate (Fig. 1) by simultaneous application of SA and Fe2O3­NPs under moderate and high salinities resulted in the production of larger seeds (Table 4). The high correlation of root and shoot parameters, seeds per plant and 1000­seed weight with seed yield (Table 5) suggests that improving these traits by breeding or foliar treatments can potentially increase crop productivity under normal and stressful conditions.Our results indicated that foliar spray of SA and SA + Fe2O3­NPs often similarly improves salt tolerance and seed yield of ajowan, so application of SA and/or SA + Fe2O3­NPs treatments can be cost­effective in reducing salinity­ induced losses in large­scale production systems. Salinity remarkably limited the root and shoot Salinity Foliar treatments Umbels per plant Seeds per plant 1000­seed weight (mg) Seed yield (g plant­1) Harvest index (%) Non­Saline Water 50.67 ± 0.42 a 6367.9 ± 56.7 a 865.7 ± 3.7 ab 5.51 ± 0.07 b 35.63 ± 0.06 a SA 51.00 ± 1.24 a 6498.5 ± 110.0 a 888.3 ± 6.0 a 5.77 ± 0.07 a 35.88 ± 0.19 a Fe2O3­NPs 52.00 ± 0.36 a 6577.6 ± 30.5 a 870.0 ± 6.8 ab 5.72 ± 0.07 a 35.84 ± 0.16 a SA + Fe2O3­NPs 51.18 ± 0.76 a 6527.8 ± 119.1 a 882.2 ± 7.0 a 5.75 ± 0.07 a 35.59 ± 0.14 a 4 dS m­1 NaCl Water 45.68 ± 0.92 b 5760.1 ± 47.0 b 829.3 ± 9.2 cd 4.78 ± 0.08 d 33.60 ± 0.28 b SA 45.22 ± 0.23 b 5751.6 ± 89.0 b 881.7 ± 4.7 a 5.07 ± 0.07 c 34.43 ± 0.17 b Fe2O3­NPs 45.83 ± 0.54 b 5874.3 ± 71.0 b 854.3 ± 8.2 bc 5.02 ± 0.07 c 34.14 ± 0.17 b SA + Fe2O3­NPs 46.83 ± 0.31 b 5919.4 ± 85.5 b 866.0 ± 3.6 ab 5.12 ± 0.06 c 34.40 ± 0.24 b 8 dS m­1 NaCl Water 33.72 ± 0.77 e 3953.6 ± 144.3 e 669.3 ± 9.6 f 2.64 ± 0.06 g 30.63 ± 0.45 d SA 39.35 ± 0.83 c 4789.9 ± 97.4 c 827.5 ± 7.0 d 3.96 ± 0.07 e 31.92 ± 0.31 c Fe2O3­NPs 36.65 ± 0.78 d 4437.6 ± 106.2 d 780.3 ± 6.9 e 3.46 ± 0.06 f 30.55 ± 0.53 d SA + Fe2O3­NPs 39.78 ± 1.00 c 4852.7 ± 120.6 c 836.2 ± 12.8 cd 4.05 ± 0.08 e 32.45 ± 0.30 c 12 dS m­1 NaCl Water 19.57 ± 0.72 g 1946.3 ± 108.7 h 605.0 ± 2.2 h 1.18 ± 0.07 j 26.10 ± 0.51 f SA 31.75 ± 0.37 e 3326.2 ± 117.0 f 687.7 ± 12.8 f 2.27 ± 0.03 h 30.19 ± 0.18 d Fe2O3­NPs 27.18 ± 1.04 f 2820.9 ± 87.3 g 630.0 ± 2.6 g 1.78 ± 0.05 i 28.47 ± 0.30 e SA + Fe2O3­NPs 33.32 ± 0.44 e 3471.7 ± 102.6 f 686.7 ± 8.8 f 2.38 ± 0.05 h 30.79 ± 0.42 d Source of variation Year (Y) NS NS NS NS NS Salinity (S) ** ** ** ** ** Foliar treatments (F) ** ** ** ** ** Y ´ S NS NS NS ** NS Y ´ F NS NS NS NS NS S ´ F ** ** ** ** ** Y ´ S ´ F NS NS NS NS NS F test 13.19** 12.73** 12.92** 32.35** 9.78** Different letters in each column indicate significant differences at p≤0.05; NS, **= No significant and significant at p≤0.01, respectively. Fe2O3­NPs= Iron­oxide nanoparticles; SA= Salicylic acid. Table 4 ­ Combined analysis of variance of the data for yield parameters of ajowan affected by salinity and foliar treatments in 2018 and 2019 Fig. 2 ­ Changes in seeds per umbel of ajowan in response to salinity. The data represents the average of three repli­ cates in two years ± standard errors. Different letters indicate significant differences at p≤0.05. Ghassemi‐Golezani and Abdoli ‐ Improving ajowan performance by foliar treatments 137 growth of ajowan, leading to lower seed yield.Negative impacts of salt stress on plant growth and productivitycould be considerably alleviated by exogenous salicylic acid and Fe2O3 nanoparticles, particularly in combined form. These beneficial effects were more pronounced under severe salinity. The ameliorative effects of SA and SA+ Fe2O3­NPs on seed yield of salt­subjected ajowan plants were mostly related to enhancing root and shoot growth, seeds per plant, seed filling rate, and 1000­seed weight. Future works may reveal other beneficial effects of different hormones and/or nanoparticles on crops under various environmental conditions. Acknowledgements We appreciate the financial support of this research by the University of Tabriz and the Iran National Science Foundation. References ABDOLI S., GHASSEMI­GOLEZANI K., 2021 ­ Salicylic acid: an effective growth regulator for mitigating salt toxicity in plants. ­ J. Plant Physiol. Breeding, 11: 1­15. ABDOLI S., GHASSEMI­GOLEZANI K., ALIZADEH­SALTEH S., 2020 ­ Responses of ajowan (Trachyspermum ammi L.) to exogenous salicylic acid and iron oxide nanoparticles under salt stress. ­ Environ. Sci. Pollut. Res. Int., 27(29): 36939­36953. 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Table 5 ­ Correlations of morphological and yield parameters of ajowan with each other Parameters Root mass Root length Shoot mass Shoot length Branches per plant Leaves per plant Seeds per plant 1000 seed weight Seed yield Harvest index Root mass 1 Root length 0.86 ** 1 Shoot mass 0.91 ** 0.94 ** 1 Shoot length 0.85 ** 0.96 ** 0.96 ** 1 Branches per plant 0.77 ** 0.80 ** 0.82 ** 0.81 ** 1 Leaves per plant 0.87 ** 0.94 ** 0.93 ** 0.93 ** 0.79 ** 1 Seeds per plant 0.90 ** 0.94 ** 0.99 ** 0.95 ** 0.79 ** 0.94 ** 1 1000­seed weight 0.90 * 0.91 ** 0.95 ** 0.92 ** 0.83 ** 0.89 ** 0.92 ** 1 Seed yield 0.90 * 0.96 ** 0.99 ** 0.97 ** 0.82 ** 0.95 ** 0.99 ** 0.95 ** 1 Harvest index 0.86 ** 0.92 ** 0.92 ** 0.92 ** 0.75 ** 0.94 ** 0.94 ** 0.91 ** 0.94 ** 1 ** Significant at p≤0.01. Adv. Hort. 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