Abstract :
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 (PGRs). More PLBs formed
per half-PLB or per PLB thin cell layer (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 for neo-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 PGRs.
