Liquid Culture Systems for in vitro Plant Propagation

498 Han Bouman & Annemiek Tiekstra
3.2 Cymbidium
The elemental analysis of adult leaves of Cymbidium is shown in table 1
and originates from Bergmann (1992). From these values, the composition
of Cymbidium adapted medium (CAM) was calculated (Table 1). As orchids
are normally grown on low-salt concentration media (in this case ½ MS,
personal communication P+S Plantlab), a N-content of 30 mmol was
adopted and on the basis of this concentration, the other elemental
concentrations were calculated. In CAM, P, Ca and Mg contents are much
higher in comparison with ½ MS. Almost no precipitation occurred, even
after autoclaving, probably because of the relatively low concentrations of
Ca and P and the relatively high concentration of sulphate. During other
adaptations, it was often observed that, while other concentrations were kept
the same, increasing salt concentration with potassium sulphate diminished
the precipitation of salts after autoclaving, possibly because sulphate has
some buffering and complex-forming capacity.
For all three cultivars, growth increased significantly by culture with
CAM compared to ½ MS and ½DKW (Table 2). For shoot formation,
rooting and acclimatisation there were no differences in mineral media and
the performance of the propagules was the same irrespective of the original
propagation medium. It is possible that further improvements could be
achieved by mineral adaptations in these steps. The nutrient concentration
ratios used in ½MS compared with those applied in hydroponics (Table 1)
are 1.5 for Ca, 1.0 for Mg and 0.76 for P. In ½DKW these ratios are 4.7, 2.0
and 1.2, respectively and in CAM 6.7, 3.7 and 2.0, respectively. This
indicates that the concentrations of Ca, Mg and P are too low in MS and -to
a lesser extent- in DKW. The CAM medium supplies these three elements at
a more appropriate concentration. For K and N in all 3 media, these ratios
are similar viz., ca. 3.5 and 5.5, respectively.
After the 3-week cycle, the media were analysed for elemental content
(data not shown). None of the major minerals was exhausted with the
notable exception of P (8 % of the original concentration remained in the
medium). Phosphorous, particularly, is known to be consumed in a ‘luxury’
way, i.e., the plant takes up more than needed for immediate growth
(George, 1993). Concerning nitrogen, it was found that the final amount of
ammonium was rather low (ca 10 % remained), but that ca 50 % of the
nitrate was still present. Especially in the CAM medium with the faster
growing plant material, sucrose concentration became low, but was not
exhausted (approximately 10 % remained).