Greenhouse production systems in New Zealand face dual challenges of limited light availability during winter and high pathogen pressure, both of which restrict productivity. Conventional responses rely on agrochemical inputs, yet these approaches are increasingly unsustainable. Recent advances in controlled-environment photobiology suggest that supplementary monochromatic red LED light can simultaneously stimulate growth and activate defence mechanisms, offering a sustainable alternative. Red light is perceived by phytochromes, triggering downstream transcriptional changes that regulate salicylic acid signalling, antioxidant enzyme activity, and secondary metabolite biosynthesis—pathways known to enhance resistance against necrotrophic pathogens such as Botrytis cinerea.
To test these effects, a glasshouse experiment was conducted at Lincoln University using lettuce as a model crop. Plants were grown under two conditions: supplementary red LED light (250 µmol m⁻² s⁻¹ for 5 h daily) and an untreated control, for ten weeks. Growth performance was evaluated by measuring shoot fresh weight (SFW) and dry weight (DW). Chlorophyll content was quantified spectrophotometrically using acetone-extracted pigments following Lichtenthaler (1987). Total phenolic content and antioxidant activity (DPPH assay) were also determined. Plants were subsequently inoculated with B. cinerea spores to assess disease severity.
Red-light supplementation increased SFW by 45% and significantly increased total chlorophyll, phenolic content, and antioxidant activity compared with controls. Disease severity was markedly reduced in red-light–treated plants: three days after inoculation, lesion length averaged 40 mm compared with 70 mm in controls, and lesion width averaged 18 mm compared with 30 mm. These findings indicate that red-light exposure not only promotes biomass accumulation but also enhances biochemical defences against B. cinerea infection.
This work underscores the potential of targeted spectral manipulation as a dual strategy for yield enhancement and disease resistance in glasshouse crops. Such findings contribute to the mechanistic understanding of light-mediated defence and provide a framework for scaling sustainable lighting strategies in controlled-environment agriculture.
