Studying the Effect of Cultivation Distance and Green Hull Extract of Walnut and Pistachio on Morphological and Biochemical Traits of Chia Plant (Salvia hispanica L.)

Background and Objective:

Chia (Salvia hispanica L.) is an annual plant belonging to the Lamiaceae family, native to Mexico and northern Guatemala. Its seeds are commercially valuable due to their high omega-3 and omega-6 content, as well as being a potential source of antioxidants and dietary fiber, making them widely used in the food and pharmaceutical industries. Given the limited cultivation of this plant in Iran, this study aimed to identify the optimal planting density and biostimulant treatments to enhance growth, increase yield, and improve the biochemical quality of chia seeds under the climatic conditions of Gorgan.

Materials and Methods:

White chia seeds were obtained from the Agricultural and Natural Resources Research and Training Center of Tehran and cultivated in a 6 × 10 m² field. The experiment was conducted in a factorial design based on a randomized complete block design (RCBD) with three replications at the research farm of Gorgan University of Agricultural Sciences and Natural Resources. Treatments included aqueous extracts of green walnut and pistachio husks at a concentration of 1000 ppm, along with different planting distances (50, 60, and 70 cm). The measured variables included morphological traits and yield components (dry weight, plant height, leaf area, number of inflorescences per plant, fresh seed weight per plant, and stem diameter), as well as phytochemical properties (total phenols, total flavonoids, antioxidant activity assessed by TAOC and FRAP methods in leaves and seeds, and seed mucilage content).

Results: The findings indicated that plant extracts and planting distances significantly influenced plant height, leaf area, number of inflorescences, fresh seed weight, and some phytochemical traits. The tallest plants (238 cm) were observed in the control treatment with a 50 cm planting distance, while the shortest plants (194 cm) were recorded in the walnut extract treatment with a 60 cm planting distance. The highest number of inflorescences (268) and fresh seed weight per plant (14.28 g) were obtained in the control treatment with a 70 cm planting distance. The largest leaf area (183.11 cm²) was found in the control treatment with a 60 cm planting distance, whereas the smallest (82.48 cm²) was observed in the walnut extract treatment with a 70 cm planting distance. Regarding phytochemical traits, the highest total phenol content in seeds (19.5 mg gallic acid. g -1 DW) was obtained in the walnut extract treatment at a 60 cm planting distance, while the highest total flavonoid content in seeds (0.66 mg quercetin. g -1 DW) was observed in the walnut extract treatment at a 70 cm planting distance. The highest antioxidant activity in seeds, as measured by the FRAP method (165.95 mg. g -1), was recorded at a 70 cm planting distance, whereas the highest antioxidant activity using the TAOC method (301 mg. g -1) was observed at a 50 cm planting distance in the walnut husk extract treatment. Additionally, the pistachio husk extract treatment at a 50 cm planting distance resulted in the highest seed mucilage content (0.1 mg g -1 DW), showing a 1.5-fold increase compared to the control at the same planting distance.

Conclusion:

The application of green walnut and pistachio husk extracts as biostimulants, along with appropriate planting density, positively influenced the growth and yield of chia plants. Both planting density and the type of extract significantly affected chia’s morphological and phytochemical characteristics. Notably, walnut husk extract played a crucial role in controlling plant height and enhancing seed antioxidant activity. These results could contribute to improving chia cultivation and productivity in similar climatic conditions while promoting the use of plant extracts in sustainable agriculture.