Optimizing in vitro mineral nutrition and plant density increases greenhouse growth of Curcuma longa L. during acclimatization

The growth of plantlets during hardening is affected by the tissue culture media in which they were grown. A multi-factor approach to optimizing nutrient ions in media for subsequent ex vitro growth has not been studied. A response surface method was designed to test in vitro plant density (50-250 buds/L), (6.25-10.25 mM), Ca2+ (2-10 mM), and KNO3 (18-100 mM) in low on medium as it affected subsequent growth in a 21 days acclimatization period with Curcuma longa genotypes (L35-1 and L22-5). The treatment media were compared with the MS medium. Plants grown on treatment media had higher relative fresh biomass (3.3 +/- 0.5 fold from high-density with 42 mM KNO3; 3.7 +/- 0.5 fold from low-density with 18 mM KNO3) than MS plants (2.6 +/- 0.5 fold) regardless of plant density. Leaf area index from the treatments (67.0 +/- 16.4 cm(2)/bud from high-density with 70.4 mM KNO3; 78.4 +/- 16.4 cm(2)/bud from low-density with 50.7 mM KNO3) was higher than MS plants (22.0 +/- 8 cm(2)/bud from high-density and 36.0 +/- 8 cm(2)/bud from low-density). Shoots from treatment plants receiving 64 mM KNO3, elongated to 8.6 +/- 0.9 cm from high-density and 10.9 +/- 0.9 cm from low-density. Genotype L22-5 elongated to 6.0 +/- 0.6 cm regardless of density, and L35-1 elongated to 6.0 +/- 0.6 cm from low-density and to 4.0 +/- 0.6 cm from high-density. Raising phosphate 5x to 10x the MS concentration in the pre-hardening media did not influence ex vitro responses. Plants grown on modified low ammonium media can grow faster and larger during acclimatization with increased KNO3, especially from high-density culture that would be preferred in commercial applications.