Introduction

The growing emphasis on sustainable and environmentally friendly production systems has intensified the search for effective alternatives to synthetic agrochemicals in floriculture. Among these alternatives, plant biostimulants have gained increasing attention due to their capacity to enhance plant growth, productivity, and stress resilience through the modulation of physiological and biochemical processes. Bromelain, a proteolytic enzyme complex derived primarily from pineapple tissues, has been extensively studied in medical and industrial applications; however, its potential role as a plant biostimulant remains largely unexplored. The present study aimed to investigate the physiological and biochemical responses of two commercially important cut rose (Rosa hybrida L.) cultivars, ‘Jumilia’ and ‘Tanja’, to foliar application of bromelain under greenhouse conditions, with particular emphasis on cultivar-specific responses and underlying regulatory mechanisms.

Materials and Methods

A factorial experiment was conducted using a randomized complete block design with three replications. Treatments consisted of two rose cultivars (‘Jumilia’ and ‘Tanja’) and three bromelain concentrations (0, 200, and 400 mg.l⁻¹). Bromelain was applied as a foliar spray at two critical phenological stages, namely bud emergence and the onset of petal coloration, to maximize its potential influence on vegetative growth and flower development. At the commercial harvest stage, a comprehensive set of morphological, physiological, and biochemical parameters was evaluated. Morphological traits included stem length and diameter, flower diameter, and fresh and dry biomass. Physiological measurements encompassed leaf relative water content (RWC), total soluble solids (TSS), proline accumulation, and membrane electrolyte leakage as an indicator of cellular stability. Biochemical analyses focused on antioxidant enzyme activities (superoxide dismutase, catalase, and peroxidase), oxidative stress markers (malondialdehyde and hydrogen peroxide), total phenolic content, lignin accumulation, and the activities of phenylalanine ammonia-lyase (PAL) and ACC synthase, a key enzyme in ethylene biosynthesis.

Results and Discussion

The results indicated that bromelain markedly affected growth performance and metabolic regulation in cut roses, with responses strongly dependent on cultivar and application rate. In ‘Tanja’, most morphological traits showed a clear quadratic pattern, reaching maximum stem length, flower size, and biomass at 200 mg.l⁻¹, followed by a significant decline at 400 mg.l⁻¹, indicating sensitivity to excessive application. In contrast, ‘Jumilia’ exhibited a more stable and predominantly linear response, with continuous improvements in growth and yield-related traits even at the highest concentration, reflecting greater adaptive capacity to bromelain-induced metabolic modulation. Physiologically, bromelain enhanced plant water relations and osmotic adjustment in both cultivars, as evidenced by increased relative water content, proline accumulation, and total soluble solids. These effects were more pronounced and persistent in ‘Jumilia’. Elevated membrane electrolyte leakage at 400 mg.l⁻¹ in ‘Tanja’ suggested membrane destabilization and the onset of stress-related damage, indicating that this concentration exceeded its tolerance threshold. Biochemically, bromelain significantly activated antioxidant defenses, increasing superoxide dismutase, catalase, and peroxidase activities while reducing malondialdehyde and hydrogen peroxide levels. These responses were strongest at the intermediate concentration, reflecting optimal regulation of redox homeostasis. Bromelain also stimulated secondary metabolism by enhancing phenylalanine ammonia-lyase activity and total phenolic content in both cultivars. Lignin accumulation increased progressively in ‘Jumilia’, whereas it peaked at 200 mg.l⁻¹ in ‘Tanja’. Additionally, bromelain reduced ACC synthase activity, suggesting suppression of ethylene biosynthesis and potential improvements in senescence regulation and postharvest quality.

Conclusion

Bromelain acted as a mild eustress-inducing biostimulant, enhancing growth–defense balance via improved antioxidant activity, osmotic regulation, and secondary metabolism. ‘Jumilia’ showed greater metabolic plasticity and tolerance to higher doses, whereas ‘Tanja’ was more sensitive. Overall, 200 mg.l⁻¹ was optimal, improving physiological resilience, biochemical stability, and yield, supporting cultivar-specific application in sustainable floriculture.