Moisture stress mitigation in gladiolus (Gladiolus grandiflorus L.) using growth regulators

Abstract

The investigation entitled ‘Moisture stress mitigation in gladiolus (Gladiolus grandiflorus L.) using growth regulators’ was conducted during 2024–2025 at the Department of Floriculture and Landscaping, College of Agriculture, Vellayani, to evaluate the impact of moisture stress and growth regulators on growth, flowering, yield, propagule production, physiological and biochemical responses, computed indices and postharvest quality in gladiolus. The experiment included the varieties Arka Amar, Arka Darshan and Arka Tilak under two moisture regimes and three growth regulator treatments; however, Arka Tilak was excluded after ten weeks due to corm rot. Overall, Arka Amar consistently outperformed Arka Darshan across most traits, and moisture stress at 75% FC reduced growth and quality, while melatonin effectively mitigated these reductions. Vegetative performance was highest in Arka Amar, with the maximum plant height of 114.63 cm recorded under 100% FC with melatonin, while Arka Darshan under stress without regulator registered the lowest height of 65.24 cm. Melatonin significantly increased shoot and root biomass, with the highest fresh and dry shoot weights (66.57 g and 43.69 g) and root weights (3.87 g fresh and 1.80 g dry) in Arka Amar under 100% FC, whereas the lowest values were recorded in Arka Darshan under stress without regulator. Flowering was advanced by melatonin and delayed by stress, with the earliest spike emergence and floret opening in Arka Amar × 100% FC × melatonin (85.37 and 96.17 days), while the maximum delay occurred in Arka Darshan × 75% FC × control (114.87 and 128.17 days). Spike quality traits were also superior in Arka Amar, with the longest spike length (97.05 cm), longest rachis (52.57 cm) and highest floret diameter (108.80 mm) under 100% FC with melatonin, whereas the poorest values were recorded in Arka Darshan under stress without regulator. Yield and propagule production showed similar trends. The highest spike weight (43.83 g) was obtained in Arka Amar under stress with melatonin and it was on par with 100% FC plus melatonin at 43.42 g, while Arka Darshan under stress control produced the 139 minimum at 22.85 g. Corm attributes were superior in Arka Amar and in melatonin-treated plants, with the largest corm diameter (4.77 cm) and maximum corm yield per plant (71.52 g) under Arka Amar × 100% FC × melatonin, whereas the lowest values were recorded in Arka Darshan × 75% FC × control. Melatonin also enhanced corm and cormel weights and sustained higher yields even under moisture stress. Postharvest quality followed the same pattern, with Arka Amar × 100% FC × melatonin achieving the longest vase life (10.50 days), highest water uptake (22.47 mL) and lowest physiological loss in weight (8.42 g). The poorest postharvest values were recorded in Arka Darshan × stress × control. Even under 75% FC, Arka Amar treated with melatonin produced flower quality comparable to well-watered plants. Physiological and biochemical analyses confirmed that melatonin improved photosynthetic activity, stomatal conductance, chlorophyll content and antioxidant enzyme activity while reducing electrolyte leakage. The best physiological performance occurred in Arka Amar × 100% FC × melatonin, which exhibited the highest photosynthesis, conductance and chlorophyll content, while the poorest functional status was seen in Arka Darshan × 75% FC × control. Stress-related biochemical markers such as proline, SOD, catalase and peroxidase increased under drought, with the strongest protective responses recorded in Arka Amar × stress × melatonin. Computed indices including leaf area index, water use efficiency and relative water content were also highest under melatonin, notably with a relative water content of 85 % in Arka Amar × 100% FC × melatonin, while the lowest value of 59.06 % occurred in Arka Darshan × stress × control. The study demonstrated that moisture stress adversely affects gladiolus growth, yield and quality. However, 100 μM melatonin and 0.3 mM brassinolide effectively alleviate these effects, with melatonin being superior. Arka Amar emerged as the most resilient and productive gladiolus variety under both optimal and water-limited conditions.