Red light and biostimulants containing arbuscular mycorrhizal fungi enhance ajmalicine and serpentine production in Catharanthus roseus under indoor conditions

Indoor farming offers optimal conditions for high and stable ajmalicine and serpentine yields in Catharanthus roseus, enabling precise control over environmental stimuli such as light and biostimulants. This study aimed to evaluate, for the first time, the combined effects of LED light spectrum and a biostimulant containing arbuscular mycorrhizal fungi on ajmalicine and serpentine production in indoor-grown C. roseus. Following a 60 days pre-treatment under white LEDs, plants received eight treatments: white (W, control), red (R), blue (B), red-blue (RB, R:B = 6:1) LED light, and their combinations with the biostimulant (BS). Samples were collected before treatments (T0) and at harvest (T1, 92 days after pre-treatment). R and RB significantly increased aerial fresh weight compared to W and B, with no significant differences in plant height relative to W. Although no mycorrhizal colonization occurred, BS significantly increased plant height, shoot fresh weight, total dry weight, leaf serpentine concentration, and total serpentine yield (+ 34.4%) compared to the untreated condition. When combined, R and BS had a synergistic effect on ajmalicine, resulting in its highest concentration and yield. Under this treatment, ajmalicine concentration and yield were significantly higher than in all other treatments (+ 144.3% and + 138.0% compared to the W control, respectively), except for the yields under B and RB with BS, which were comparable to those under R with BS. From T0 to T1, total serpentine yield increased by 2277.1%, while ajmalicine yield rose by 716.0%. In conclusion, the combined application of R and BS, followed by harvest after a 92 days treatment period, is the most effective strategy to optimize ajmalicine and serpentine production while ensuring vigorous yet size-controlled plant growth.