Faculty of Agriculture and Graduate School of Agriculture, Kagawa University, Miki-cho, Kagawa, 761-0795, Japan Present address: P. O. Box 7, Miki-cho post office, Ikenobe 3011-2, Kagawa-ken, 761-0799, Japan
Carbon and nitrogen are the two elements that most affect plant organogenesis.
In vitro, usually as part of the macronutrients. Some anecdotal evidence from the literature suggests that the ammonium (NH4+) to nitrate (NO3–) ratio may affect orchid organogenesis. In this study, to test this hypothesis, different NH4+: NO3– ratios were tested on the development of protocorm-like bodies (PLBs) of hybrid Cymbidium Twilight Moon ‘Day Light’, when modified in Teixeira Cymbidium (TC) No.1 medium without plant growth regulators. More PLBs formed per half-PLB or per PLB tTCL when TC medium was used while TC from which PGRs or NO3–or NH4+ were removed (two controls) contained significantly less PLBs/explant. The same trend was observed forneo -PLB (i.e., newly formed PLB) fresh weight. A high NO3– ratio favoured neo -PLB formation, but always less than TC medium, but significantly higher than the two controls. tTCLs performed more poorly (i.e., fewer neo-PLBs/explant and lower fresh weight) than half-PLBs. The NH4+: NO3– ratio can be manipulated to increase the level of PLB production in the absence of plant growth regulators.