The Effect of Auxin and Chitosan Elicitors on Yield and Selected Quantitative and Qualitative Traits of Aloe vera (Aloe barbadensis Miller)



Introduction

Aloe vera (Aloe barbadensis Miller) is recognized as one of the most important medicinal plants worldwide due to its extensive therapeutic, cosmetic, and nutritional applications. The global economic importance of this species is substantial, with a high market value for both raw materials and processed products. Therefore, improving both yield and quality-related traits of Aloe vera has become an important research objective.Among the various agronomic strategies, the application of plant growth regulators (PGRs) and biostimulants has emerged as an effective approach to enhance plant growth, physiological performance, and metabolite accumulation. Auxin, as a key plant hormone, regulates cell elongation, division, and differentiation, while chitosan, a natural biopolymer, has been widely investigated for its role in stimulating plant growth and secondary metabolite production. Despite numerous studies on different crops, limited information is available regarding the combined effects of auxin and chitosan on Aloe vera. The present study was conducted to evaluate the influence of auxin and chitosan-based elicitor applications on yield and selected quantitative and qualitative attributes of Aloe vera.

Materials and Methods

A factorial experiment based on a randomized complete block design (RCBD) with four replications was carried out in the greenhouse of the Isfahan Agricultural and Natural Resources Research Center, Iran. Treatments consisted of four concentrations of auxin (NAA)(0, 500, 1000, and 1500 mg L⁻¹) and four concentrations of chitosan (0, 250, 500, and 1000 mg L⁻¹). Uniform clonal plantlets with four leaves and identical genetic backgrounds were transplanted into pots containing an equal mixture of well-decomposed farmyard manure, soil, and sand. After transplanting, pots were uniformly arranged, irrigated twice weekly, and weeded regularly for a 10-month growth period. The first foliar spray was applied at the six-leaf stage and the second at the ten-leaf stage. Two months after the second application, the following parameters were recorded: number of leaves, number of offshoots, leaf diameter, plant height, gel percentage, total yield, gel yield, and photosynthetic pigments (chlorophyll a, b, and carotenoids).

Results and Discussion

The results showed that auxin significantly influenced plant growth, particularly plant height, which increased with auxin concentration up to 1000 mg L⁻¹, likely due to its role in promoting cell elongation and apical dominance. However, further increase in auxin concentration did not significantly enhance plant height, indicating a saturation effect. In contrast, leaf number decreased with increasing auxin concentration, suggesting a shift in assimilate allocation toward vertical growth rather than leaf proliferation. Neither auxin nor chitosan significantly affected the number of suckers, indicating that these treatments had limited influence on vegetative propagation under the experimental conditions.

A significant interaction between auxin and chitosan was observed for leaf weight and thickness, demonstrating a synergistic effect of these treatments on leaf development. The highest leaf weight was obtained with 1000 mg L⁻¹ auxin combined with 500 mg L⁻¹ chitosan, while optimal leaf thickness occurred at moderate auxin levels. This enhancement can be attributed to improved water retention, nutrient uptake, and cell expansion induced by chitosan, along with auxin-mediated growth regulation. However, excessive auxin levels appeared to reduce these traits, supporting previous findings that high auxin concentrations may inhibit cell expansion.

Yield and gel-related traits responded strongly to both treatments and their interaction. The highest gel percentage was achieved at the highest levels of auxin (1500 mg L⁻¹) and chitosan (1000 mg L⁻¹), whereas maximum plant yield and gel yield were obtained with 1000 mg L⁻¹ auxin combined with 500 mg L⁻¹ chitosan. These results suggest that moderate concentrations are more effective for maximizing overall productivity, while higher concentrations may primarily enhance gel concentration rather than total biomass. The observed yield improvement can be explained by enhanced photosynthetic efficiency, delayed leaf senescence, and improved assimilate translocation induced by auxin and chitosan.

Biochemical analyses further supported these findings. Chlorophyll a and b contents increased with auxin application up to 1000 mg L⁻¹, followed by a decline at higher concentrations, indicating that optimal auxin levels promote pigment synthesis while excessive levels may disrupt metabolic balance. Chitosan significantly increased chlorophyll content across all concentrations, likely due to its role in enhancing nutrient uptake and photosynthetic activity. Carotenoid content was primarily affected by chitosan and increased with its concentration, suggesting improved antioxidant capacity and stress tolerance.

Gel carbohydrate content was significantly enhanced by both auxin and chitosan, with higher concentrations leading to substantial increases compared to the control. This increase may be attributed to the role of auxin in regulating carbohydrate metabolism and the ability of chitosan to enhance photosynthesis and carbon–nitrogen balance. The combined application of these treatments likely improved enzymatic activity involved in sugar synthesis and accumulation.

Conclusion

Overall, the combined application of auxin and chitosan elicitors significantly improved the growth performance, yield, and biochemical traits of Aloe vera. Co-application of these regulators had more pronounced effects compared to their individual use. Therefore, a combined treatment of 1500 mg L⁻¹ auxin and 1000 mg L⁻¹ chitosan is recommended to maximize gel percentage, whereas the combination of 1000 mg L⁻¹ auxin and 500 mg L⁻¹ chitosan is optimal for achieving higher leaf and gel yields.