Manipulation of light spectral quality for inducing off-season flowering in Jasminum sambac cv. CO.1 (Gundumalli)

Jasminum sambac cv. CO.1 (Gundumalli), a commercially important fragrant flower crop of South India, experiences a marked decline in production during winter months (November to February), limiting year-round market availability. The present investigation evaluated the influence of driplock diffused polyfilm (light transmission 87 %; diffusion 62 %) as a polytunnel cladding material in combination with end-of-day (EOD) photoperiodic (light emitting diode (LED)) lighting (4 hr, 18:00–22:00 hr) under different spectral regimes on off-season flowering in CO. 1 (Gundumalli). The experiment was conducted in Mettupalayam, Coimbatore, Tamil Nadu, India during November 2024 – February 2025 in randomised block design (RBD) with 5 treatments and 4 replications. Treatments included open field control (T1), polytunnel without supplemental light (T2), polytunnel with 60 % red : 20 % blue : 20 % far-red (T3), polytunnel with 80 % red : 20 % blue (T4) and polytunnel with 80 % red : 20 % far-red (T5). Treatment T₅ significantly improved flower yield and quality parameters compared with other treatments (p ≤ 0.05), recording the highest pooled mean number of flower cymes (42.26 per plant), flower buds per plant (194.37), flower yield per plant (52.53 g), weight of 100 buds (28.49 g), length of flower bud (2.42 cm), length of corolla tube (1.59 cm) and width of flower bud (0.95 cm). Based on the pooled mean values, Treatment T₅ resulted in approximately 5–6-fold higher values for these parameters than the open-field control. The diffused polyfilm structure maintained mean temperatures 3–5 °C higher than ambient, facilitating sustained flower bud initiation during the cold season. The superior performance of the 80 % red : 20 % far-red spectrum may be attributed to enhanced phytochrome-mediated flowering responses. These findings demonstrate the potential of integrating a diffused polyfilm polytunnel with EOD LED spectral lighting as an effective strategy for improving off-season jasmine production under protected cultivation.