No abstract

A simple picrate paper kit method was developed for the semiquantitative determination of the cyanogenic potential for cassava flour. The method involved the addition of linamarase and pH 8 phosphate buffer (absorbed in a filter paper disc) to 100 mg of flour +0·5 ml water placed in a small vial. A rectangle of yellow picrate paper attached to a plastic strip was added and the vial capped and left overnight. The yellow paper changed colour towards brown and its colour was compared with that of a standard colour card with 10 shades of colour which corresponded with cyanogenic potentials of 0–800 mg HCN equivalents kg−1 flour (ppm). To obtain a more accurate measure of cyanogenic potential (±20%) the paper was eluted with water and the absorbance measured at 510 nm. The cyanogenic potential in ppm was determined from a calibration graph. The methodology is available in kit form. The simple method may be used in the field by a relatively unskilled person. The more accurate method requires a spectrophotometer and is suitable for use in simple laboratories in developing countries. © 1998 SCI.

Plantlets of Dendrobium Chao Praya Smile maintained in vitro were induced to flower, which produced viable seeds within about 11 months. A two-layer (Gelrite-solidified layer topped with a layer of liquid medium of the same volume and composition) culture system containing benzyladenine (BA) at 11.1 muM induced the highest percent of flowering (45%) in plantlets within 6 months from germination. The percentage of inflorescence induction was increased to 72% by pre-selecting morphologically normal seedlings prior to two-layer culture. Plantlets in culture produced both complete (developmentally normal but smaller than flowers of field grown plants) and incomplete flowers. Pollen and female reproductive organs of in vitro-developed complete flowers were morphologically and anatomically similar to flowers of field grown plants. In addition, 65% of the pollen grains derived from in vitro-developed flower were tetrad suggesting that regular meiosis occurred during microsporogenesis. The percentage of germination of pollen grains derived from in vitro-developed flowers and flowers of field grown plants, incubated on modified Knops' medium for 8 days, were 18.2 and 52.8%, respectively. Despite a lower percentage of germination of the pollen grains derived from in vitro-developed flowers, flowers induced in culture could be self-pollinated and developed seedpods with viable seeds. Nearly 90% of these seeds developed into protocorms on germination in vitro. These seedlings were grown in culture and induced to flower in vitro again using the same procedure.