Effect of Different Light Quality and Photoperiod on Mycelium and Fruiting Body Growth of Tricholoma giganteum

Light is a crucial environmental regulator for <i>Tricholoma giganteum</i> (<i>T. giganteum</i>). This study investigated the effects of light quality and photoperiod on its growth, physiology, and nutritional composition. During the mycelial stage, blue light (BL) exposure for 5 d promoted the highest growth rate (0.74 mm d^-1, 45% higher than dark control, <i>p</i> < 0.05). Red light (RL) enhanced antioxidant capacity, elevating superoxide dismutase (SOD) activity to 240.20 U·mL^-1 (after 5 d) and DPPH radical-scavenging activity to 276.11% (after 3 d). Ultraviolet (UV) suppressed polyphenol oxidase (PPO) activity. BL also increased mycelial polysaccharide content (6.45 g·100 g^-1). In the fruiting stage, green light (GL) improved agronomic traits and first-grade yield (3.75 kg), while also promoting the accumulation of glutamate (4.39 g·100 g^-1), a key umami compound. Further photoperiod optimization revealed that 4 h of daily GL exposure shortened the fruiting cycle, achieved the highest biological efficiency (98.4%), and maximized both polysaccharide (38.17 g·100 g^-1) and glutamate contents (5.70 g·100 g^-1). These results recommend a two-stage lighting protocol: BL for mycelial growth and a 4 h daily GL for fruiting, providing a scientific basis for the industrial cultivation of <i>T. giganteum</i>.