Abstract
The objective of this study was to improve the growth of in vitro shoot cultures of Brugmansia × candida 'Creamsickle'. Several mineral nutrient experiments were conducted to determine the effect of NH4 (+), NO3 (-), K(+), FeSO4/EDTA, ZnSO4, MnSO4, and CuSO4 on quality, leaf width and length, size and weight of shoot mass, and shoot number. The experiment to determine the levels of NH4 (+), NO3 (-), and K(+), was conducted as a 2-component NH4 (+): K(+) mixture crossed by [NO3 (-)] and resulted in an experimental design free of ion confounding and capable of separating the effects of proportion and concentration. The results of the NH4 (+)-K(+)-NO3 (-) experiment revealed a region in the design space where growth was significantly improved; the region generally had lower total nitrogen and lower NH4 (+):K(+) ratios than MS medium. The experiments to determine the appropriate levels of Fe, Zn, Mn, and Cu were conducted at six log levels ranging from 0 to 1 mM. Of the four metal salts tested, MnSO4 had the least effect on in vitro shoot growth and its concentration was reduced from 0.1 mM (MS level) to 0.001 mM. CuSO4 had large effects on in vitro shoot growth and was increased from 0.0001 mM to 0.001 mM. A 2-level factorial of NH4 (+)-K(+)-NO3 (-), FeSO4/EDTA, and ZnSO4 was conducted and several formulations identified for their improvements of quality and growth. In addition to the changes to MnSO4 and CuSO4, these formulations were characterized by lower levels of NH4 (+), K(+), NO3 (-) and Zn, and higher levels of FeSO4/EDTA. Overall, several nutrient formulations were identified as superior to MS medium for growth of in vitro shoot cultures of B. 'Creamsickle'.