Multi-factor models to resolve growth responses in vitro and during subsequent greenhouse growth for turmeric (Curcuma longa L.)

Plant media has been developed over the last six decades, yet, there has not been medium optimized for microplant greenhouse growth, which may be important for producing chemical compounds and preparing transplants for success in the field. A series of multi-factor optimization experiments were conducted on turmeric (Curcuma longa L., genotype L 35-1) to identify the effects of mineral nutrition and plant density in vitro on laboratory and greenhouse production. The first experiment optimized PO43-, Ca2+, Mg2+, and KNO3 for five-months growth in bioreactors with periodic supplementation of sucrose solution +/- nutrients. Phosphorus (6.25 mM) increased sucrose supplement and rhizome dry biomass. However KNO3 (60 mM) increased water supplement and fresh plant biomass. Two optimal media were developed for plant multiplication based on in vitro plant density, whereas high plant density required 9 mM Ca2+ and 60 mM KNO3 and low plant density required 3 mM Ca2+ and 20 mM KNO3. Bioreactor plants were transferred to the greenhouse for 6-months and fertilized with either high- or low-input fertilizer. Large bioreactor plants developed with 6.25 mM PO43-, but in the greenhouse plants had more offsets and grew larger with receiving less than 6.25 mM PO43- and less than 6 mM Ca2+ media. Mineral interactions affected curcuminoids concentration in greenhouse finished dry rhizomes regardless of plant density under high-input fertilizer. Curcumin concentration increased with low-input fertilizer 6 buds/vessel and 6.25 mM PO43-. Another mineral experiment was conducted on genotypes L35-1 and L22-5 and compared various optimized media to an MS control. Regardless of genotype, 5 mM NH4+, moderate KNO3, and 2 mM Ca2+ yielded plants with longest shoots and largest leaves after a 21d acclimatization period. Results concluded that high plant density combined with proper mineral nutrition yielded more plants in vitro that continued to grow better during subsequent greenhouse growth. There was consensus across experiments of optimal media for greenhouse responses that differed from what was optimal in vitro. Optimizing in vitro medium for turmeric greenhouse growth can be used as a model to identify optimum medium for other crops, so laboratories can create more value for their customers.