Polyamines (PAs) are small aliphatic compounds that function as important plant biostimulants, contributing to growth regulation, development, and responses to environmental stresses. Among these compounds, putrescine (Put) has gained considerable attention for its potential role in improving plant tolerance to abiotic stresses, especially drought conditions. This study investigated the effects of varying irrigation intervals and exogenous Put application on growth performance and antioxidant responses of Petunia × hybrida cv. Grandiflora. The experiment was conducted using a factorial completely randomized design with three replications, including four irrigation regimes (2, 4, 6, and 8-day intervals) and four Put concentrations (0, 0.5, 1.0, and 1.5 mM). Extended irrigation intervals negatively affected plant growth parameters and photosynthetic pigment levels, demonstrating the detrimental effects of water limitation. However, Put treatment mitigated drought-induced damage and improved several physiological traits. The highest soluble sugar accumulation and guaiacol peroxidase activity were recorded in plants subjected to an 8-day irrigation interval with 1.5 mM Put. Catalase activity was greatest under severe drought conditions without Put supplementation, while carotenoid content was lowest in plants treated with 0.5 mM Put under adequate irrigation. Altogether, the significant interaction between irrigation frequency and Put concentration on growth and biochemical characteristics indicates that Put application may enhance drought tolerance and support physiological stability in petunia under water-limited conditions.
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